Tropical Storm Leslie

Post-Tropical Storm Leslie 1700 Hours October 13 2018
Post-Tropical Storm Leslie 1700 Hours October 13 2018

NWS National Hurricane Center Miami FL 500 PM AST Sat Oct 13 2018

After a total of 70 advisories, long-lived Leslie has become post-tropical just west of the coast of Portugal, finally succumbing to the combination of cool waters, strong vertical wind shear, and interaction with an approaching cold front. The air mass ahead of the cyclone has moistened up in the low levels with Faro, Portugal, reporting a dewpoint of 70F/21C, but the dewpoints across central and northern Portugal ahead of Leslie are only in the low-60F range, which is not indicative of a tropical air mass. Thus, the cyclone is now a powerful post-tropical low pressure system that even has a partial eye noted in the most recent 2000Z Portuguese composite radar imagery. After landfall, rapid weakening is anticipated, and Leslie is forecast to degenerate into a broad low pressure area over or just north of Spain by late Sunday.

Leslie is moving quickly toward the northeast or 050/30 kt. Post-tropical Cyclone Leslie should continue in a fast northeastward direction for the next 12-18 hours, making landfall near or just south of Porto, Portugal by 14/0000Z. This forecast motion is consistent with the previous advisory and the latest track model guidance.

The meteorological services of Portugal and Spain are handling hazards information for their respective countries via local weather products. This is the last National Hurricane Center (NHC) advisory on this system.

Key Messages:

1. Leslie is expected to bring near hurricane-force winds to portions of Portugal later tonight as a powerful post-tropical cyclone. Gale-force winds are also likely to affect portions of northwestern and northern Spain tonight and Sunday.

2. Leslie is expected to produce rainfall amounts of 25 to 75 mm (1 to 3 inches) with isolated amounts as high as 125 mm (5 inches) across portions of Portugal and Spain, which could cause flash flooding.

3. For more information on Leslie, interests in Portugal should refer to products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt. Interests in Spain should refer to products from the State Meteorological Agency at www.aemet.es.

FORECAST POSITIONS AND MAX WINDS

INIT  13/2100Z 40.5N   9.5W   60 KT  70 MPH - Tropical Storm (WSW Vagos, Portugal)
 12H  14/0600Z 43.0N   4.9W   35 KT  40 MPH - Post Tropical ( Barniedo de la Reina, Spain)
 24H  14/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 800 AM AST Sat Oct 13 2018

Hurricane Leslie

8:00 AM AST Sat Oct 13
Location: 37.3°N 14.5°W
Moving: ENE at 38 mph
Min pressure: 980 mb
Max sustained: 75 mph

NWS National Hurricane Center Miami FL 500 AM AST Sat Oct 13 2018

Hurricane Leslie –  Satellite imagery suggests that Leslie has started extratropical transition. The mid-level eye seen earlier in both conventional and microwave satellite imagery has become less distinct, and it is continuing to separate from the low-level center. In addition, colder air is entraining into the western and southern sides of the circulation. However, a sizable cluster of convection persists to the northeast of the center, indicating that the cyclone is still tropical at this time. The large-scale models forecast that Leslie will likely complete transition in 12 to perhaps 18 h, and that the associated winds should remain at or near hurricane force until the center moves over the Iberian Peninsula. After landfall, rapid weakening is forecast, and the cyclone should dissipate as it becomes part of a broad low pressure area over Spain between 36-48 h.

The initial motion is 070/33 as Leslie is now well embedded in the mid-latitude westerlies. A continued east-northeastward motion with a gradual decrease in forward speed is expected for the next 36 h. This should bring the center of Leslie onshore on the Iberian Peninsula in about 18 h and into western Spain by about 24 h. There is little change in either the track guidance or the track forecast from the last advisory. The meteorological services of Portugal and Spain will handle hazard information for their respective countries via local weather products.

Key Messages:

1. Leslie is expected to bring near hurricane-force winds to portions of Portugal late today as a powerful post-tropical cyclone. Gale-force winds are also likely to affect portions of western Spain tonight and Sunday.

2. Leslie is expected to produce rainfall amounts of 25 to 75 mm (1 to 3 inches) with isolated amounts as high as 125 mm (5 inches) across portions of Portugal and Spain, which could cause flash flooding.

3. For more information on Leslie, interests in Portugal should refer to products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt. Interests in Spain should refer to products from the State Meteorological Agency at www.aemet.es.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 36.2N  16.7W   65 KT  75 MPH - Category 1 (WSW Albufeira, Portugal)
 12H  13/1800Z 37.7N  11.8W   65 KT  75 MPH - Category 1 (WSW Sines, Portugal)
 24H  14/0600Z 39.6N   6.8W   35 KT  40 MPH - Tropical Storm ( Brozas, Spain)
 36H  14/1800Z 41.3N   2.7W   25 KT  30 MPH - Tropical Storm (Marazovel, Spain)
 48H  15/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Fri Oct 12 2018

Although Leslie  continues to produce a compact area of deep convection, microwave data since the previous advisory indicate that the mid-level center is becoming more separated from the low-level center due to increasing shear. Dvorak final-T numbers have begun to decrease a bit, and the initial intensity is therefore set at 70 kt. A cold front is beginning to wrap around the western side of Leslie’s circulation, and the global models indicate that the cyclone should lose its warm core and become fully embedded within the frontal zone by 24 hours, if not sooner. Despite sea surface temperatures of 17-23 degrees Celsius ahead of Leslie, baroclinic forcing is likely to maintain the system’s intensity as it becomes extratropical. As a result, Leslie is forecast to reach the Iberian Peninsula as a hurricane-force extratropical low, with the NHC intensity forecast most closely following the GFS guidance. Rapid weakening is forecast once the low moves inland, and the system should dissipate over the higher terrain of Spain in about 48 hours.

The forward motion is east-northeastward, or 075/31 kt. Located within the base of a progressive trough, Leslie should maintain this trajectory, slowing down only a little bit before it reaches Portugal and Spain in 24-36 hours. Except for the UKMET model, which shows Leslie turning more northeastward toward the northwestern Iberian Peninsula, the rest of the track guidance is tightly clustered and brings the center inland across central Portugal and western Spain. Because most of the models are in good agreement and are close to the previous official forecast, no significant changes were made to the NHC forecast on this cycle.

Based on coordination from earlier today, the meteorological services of Portugal and Spain will handle hazard information for their respective countries via local weather products.

Key Messages:

1. Leslie is expected to bring near hurricane-force winds to portions of Portugal late Saturday as a powerful post-tropical cyclone. Gale-force winds are also likely to affect portions of western Spain Saturday night and Sunday.

2. Leslie is expected to produce rainfall amounts of 25 to 75 mm (1 to 3 inches) with isolated amounts as high as 100 mm (4 inches) across portions of Portugal and Spain, which could cause flash flooding.

3. For more information on Leslie, interests in Portugal should refer to products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt. Interests in Spain should refer to products from the State Meteorological Agency at www.aemet.es.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0300Z 34.7N  20.7W   70 KT  80 MPH - Category 1 (WNW Funchal, Madeira)
 12H  13/1200Z 36.5N  15.4W   65 KT  75 MPH - Category 1 (WSW Lagos, Portugal)
 24H  14/0000Z 38.9N   9.4W   65 KT  75 MPH - Category 1 (São João das Lampas, Portugal)
 36H  14/1200Z 41.0N   5.1W   40 KT  45 MPH - Tropical Storm (San Cristóbal de Trabancos, Spain)
 48H  15/0000Z 42.3N   1.1W   25 KT  30 MPH - Tropical Storm (Malpica de Arba, Spain)
 72H  16/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Fri Oct 12 2018

Hurricane Leslie’s  cloud pattern continues to feature a central dense overcast, but with only hints of an eye in visible imagery. A partial northern eyewall was noted on a 0910Z SSMIS overpass. Dvorak intensity estimates have decreased slightly, and based on this, the initial intensity has been conservatively nudged down to 75 kt. The wind field is quite large, especially south of the center, as confirmed by a pair of recent ASCAT passes, and the initial wind radii have been adjusted using those data.

The initial motion estimate is now 070/28. Leslie is moving quickly east-northeastward on the southern side of a powerful longwave trough centered over the north Atlantic. The track forecast reasoning has changed since the last advisory, with the GFS, ECMWF, and now the 06Z run of the UKMET all showing a more eastward motion of Leslie toward the Iberian Peninsula as the cyclone is picked up by the aforementioned trough. The new NHC track forecast has been adjusted significantly to the north and east, especially beyond 24 hours, but still lies to the south of and is slower than the GFS and ECMWF. Once the system moves inland, the low-level center should dissipate over the high terrain, but a 72 hour remnant low point is included for continuity purposes. Needless to say, confidence in the official track forecast beyond 24 hours is quite low given the recent shift in the models, and further adjustments will likely be necessary.

The intensity forecast shows Leslie only slowly weakening as a tropical cyclone during the next 24 hours due to a combination of cool SSTs and increasing shear from the trough. However, simulated satellite imagery and model fields suggest that Leslie will transition to a powerful post-tropical cyclone by 36 hours, likely still at hurricane intensity as shown by the global models. Weakening is expected after the trough passes Leslie by, and the mid-level circulation will likely be sheared away by strong upper-level winds.

Leslie is expected to bring significant rain and wind impacts to portions of Portugal and Spain by Sunday, and residents in those areas should refer to products from their local meteorological services for more information on these hazards.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 33.0N  28.0W   75 KT  85 MPH - Category 1 (WSW Funchal, Madeira)
 12H  13/0000Z 34.2N  23.0W   70 KT  80 MPH - Category 1 (WNW Funchal, Madeira)
 24H  13/1200Z 35.4N  17.0W   65 KT  75 MPH - Category 1 (WSW Lagos, Portugal)
 36H  14/0000Z 36.0N  12.5W   65 KT  75 MPH - Category 1 (WSW Lagos, Portugal)
 48H  14/1200Z 36.3N   9.1W   50 KT  60 MPH - Tropical Storm (WSW Lagos, Portugal)
 72H  15/1200Z 37.0N   4.0W   20 KT  25 MPH - Tropical Storm (Alhama de Granada, Spain)
 96H  16/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Fri Oct 12 2018

Hurricane Leslie’s cloud pattern continues to feature a central dense overcast, but with only hints of an eye in visible imagery. A partial northern eyewall was noted on a 0910Z SSMIS overpass. Dvorak intensity estimates have decreased slightly, and based on this, the initial intensity has been conservatively nudged down to 75 kt. The wind field is quite large, especially south of the center, as confirmed by a pair of recent ASCAT passes, and the initial wind radii have been adjusted using those data.

The initial motion estimate is now 070/28. Leslie is moving quickly east-northeastward on the southern side of a powerful longwave trough centered over the north Atlantic. The track forecast reasoning has changed since the last advisory, with the GFS, ECMWF, and now the 06Z run of the UKMET all showing a more eastward motion of Leslie toward the Iberian Peninsula as the cyclone is picked up by the aforementioned trough. The new NHC track forecast has been adjusted significantly to the north and east, especially beyond 24 hours, but still lies to the south of and is slower than the GFS and ECMWF. Once the system moves inland, the low-level center should dissipate over the high terrain, but a 72 hour remnant low point is included for continuity purposes. Needless to say, confidence in the official track forecast beyond 24 hours is quite low given the recent shift in the models, and further adjustments will likely be necessary.

The intensity forecast shows Leslie only slowly weakening as a tropical cyclone during the next 24 hours due to a combination of cool SSTs and increasing shear from the trough. However, simulated satellite imagery and model fields suggest that Leslie will transition to a powerful post-tropical cyclone by 36 hours, likely still at hurricane intensity as shown by the global models. Weakening is expected after the trough passes Leslie by, and the mid-level circulation will likely be sheared away by strong upper-level winds.

Leslie is expected to bring significant rain and wind impacts to portions of Portugal and Spain by Sunday, and residents in those areas should refer to products from their local meteorological services for more information on these hazards.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 33.0N  28.0W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  13/0000Z 34.2N  23.0W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  13/1200Z 35.4N  17.0W   65 KT  75 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  14/0000Z 36.0N  12.5W   65 KT  75 MPH - Category 1 (WSW Faro, Portugal)
 48H  14/1200Z 36.3N   9.1W   50 KT  60 MPH - Tropical Storm (WSW Lagos, Portugal)
 72H  15/1200Z 37.0N   4.0W   20 KT  25 MPH - Tropical Depression (Alhama de Granada, Spain)
 96H  16/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Thu Oct 11 2018

Hurricane Leslie’s inner-core structure has improved a little during the day today. A ragged banding eye was present in visible imagery until sunset, though this feature is not apparent in IR imagery. Recent satellite intensity estimates range from 65 kt to 90 kt, so Leslie’s intensity has been raised to 75 kt as a compromise of all available estimates.

Leslie continues to accelerate east-northeastward with an initial motion estimate of 065/18 kt. Confidence remains high that Leslie will continue gaining speed on that heading for the next 24 h or so. Beyond that time, the ensemble spread is still very high, though the 12Z deterministic global models are generally in agreement that Leslie will separate from a mid-level trough, slow down, and turn southward over the weekend. While the exact timing of this turn is still highly uncertain, the multi-model consensus brings Leslie near Madeira Island on Saturday as a tropical storm. The new official forecast shows a very similar track, and the government of Portugal has issued a Tropical Storm Watch for that island. While the exact path of Leslie is still uncertain, the cyclone is still expected to produce tropical storm conditions over a wide area through Saturday, and interests on Madeira should not focus on the exact track of Leslie.

No large changes in intensity are anticipated during the next 24 h, though some fluctuations are possible, up or down. By 36 h, Leslie will reach much cooler waters and encounter an increase in wind shear which should lead to steady weakening. The intensity guidance is in surprisingly good agreement given the continued large track spread, and the NHC intensity forecast is near the middle of the guidance envelope from 36 h onward. By 96 h, odds are increasing that Leslie could lose all of its convection and become post-tropical, though this possibility still depends heavily on Leslie following a track similar to the NHC official forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 29.9N  36.5W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  12/0600Z 31.0N  33.0W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  12/1800Z 32.5N  27.4W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  13/0600Z 33.3N  21.6W   65 KT  75 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 48H  13/1800Z 33.1N  17.4W   55 KT  65 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  14/1800Z 30.9N  16.0W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 96H  15/1800Z 29.0N  18.5W   30 KT  35 MPH - Tropical Storm (WNW Santa Cruz de La Palma, Canary Islands)
120H  16/1800Z 28.0N  24.0W   30 KT  35 MPH - Tropical Storm (WSW Villa de Valverde, Canary Islands)

NWS National Hurricane Center Miami FL 1100 AM AST Thu Oct 11 2018

Hurricane Leslie structure has remained steady since last night. The hurricane has a ragged banding eye surrounded by a somewhat patchy central dense overcast. Recent Dvorak classifications from TAFB and SAB are unchanged, and still support an initial intensity of 70 kt.

For days now, it has been clear that Leslie will accelerate east-northeastward on the south side of a mid-latitude trough moving across the North Atlantic. That acceleration is well underway now, and the initial motion estimate is 060/14 kt. It has been unclear, however, when (or if) Leslie could separate from this trough and begin to drift southward over the eastern Atlantic. The model spread has remarkably increased since yesterday, and nearly 1/3 of the members of the most recent GFS and ECMWF ensemble runs no longer forecast Leslie to separate from the trough at all, instead showing the cyclone approaching western Europe as an extratropical low. Even the deterministic model spread has increased, and the two NOAA regional hurricane models, the HWRF and HMON, are nearly 2300 miles apart at day 5. Through 48 h, the official track forecast is very similar to the previous advisory, but it has been adjusted eastward beyond that time, to bring it closer to the most recent deterministic multi-model consensus. Confidence in the track forecast is not high at 72 h and beyond, and it’s possible that large changes could still be required to future advisories.

Leslie should remain in a generally favorable environment for strengthening during the next 24-36 h, and slight intensification is still expected, though the official intensity forecast is now on the high side of the guidance through this period. By 48 h and onward, Leslie will be moving into a far more stable environment and over cooler waters, so steady weakening is anticipated. If Leslie follows a track similar to the NHC forecast, it will likely become a weak post-tropical low within 96 h. However, if Leslie undergoes extratropical transition, its worth noting that the maximum winds associated with the cyclone would likely be higher than indicated here.

FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 29.1N  38.3W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  12/0000Z 30.3N  35.5W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 24H  12/1200Z 31.7N  30.3W   75 KT  85 MPH - Category 1 (WSW Funchal, Madeira)
 36H  13/0000Z 32.8N  24.6W   70 KT  80 MPH - Category 1 (WSW Funchal, Madeira)
 48H  13/1200Z 33.2N  20.0W   60 KT  70 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  14/1200Z 31.3N  17.3W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 96H  15/1200Z 29.1N  19.0W   30 KT  35 MPH - Tropical Storm (WNE La Palma, Canary Islands)
120H  16/1200Z 27.5N  24.0W   30 KT  35 MPH - Tropical Storm (WSW Villa de Valverde, Canary Islands)

NWS National Hurricane Center Miami FL 500 AM AST Thu Oct 11 2018

Hurricane Leslie – The cloud pattern of Leslie has not changed significantly overnight. The hurricane has a large and ragged eye with deep convection most organized on its east side. The Dvorak CI-numbers are unchanged at 4.0/65 kt from TAFB and 4.5/77 kt from SAB, and based on these data, the initial intensity is held at 70 kt.

Leslie will remain in low wind shear conditions and over relatively warm waters for another day or two, so little change in strength is expected during that time. Thereafter, the hurricane is forecast to move over waters as cool as 24 deg C and into an atmospheric environment of stronger shear and drier air. All of these conditions point to a weakening trend, which is likely to begin by the weekend. Most of the guidance shows a cold front approaching Leslie, but not quite merging with it so extratropical transition is not expected. However, it seems likely that Leslie will lose its convection and become a weaker post-tropical low in about 4 days. This scenario is supported by the latest runs of the GFS, ECMWF, and HWRF models.

Leslie has made the expected east-northeastward turn with the latest initial motion estimated to be 065/9. This east-northeastward motion with an increase in forward speed is forecast to continue for the next 2 days while the steering pattern holds. After that time, however, it becomes much less clear. The models continue to struggle and keep changing their tune cycle to cycle on whether or not Leslie continues east-northeastward toward Morocco or Portugal, or gets left behind and moves west-southwestward due to a building ridge. The ensemble members of both the GFS and ECMWF favor the left behind (or southwestward) solution, and the NHC track forecast continues to lean in that direction. This forecast does show Leslie moving farther east before it makes the southwestward turn to be in better agreement with the latest consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  11/0900Z 28.4N  40.1W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  11/1800Z 29.3N  37.8W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  12/0600Z 30.9N  33.3W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  12/1800Z 32.1N  27.5W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 48H  13/0600Z 32.7N  22.3W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 72H  14/0600Z 31.3N  18.7W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
 96H  15/0600Z 29.0N  19.5W   35 KT  40 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
120H  16/0600Z 27.5N  24.5W   30 KT  35 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 1100 PM AST Wed Oct 10 2018

Hurricane Leslie   – The overall cloud pattern of Leslie has become somewhat better organized over the past several hours with increasing convection in the central dense overcast and tighter banding features. A blend of the subjective Dvorak and microwave estimates suggest an initial wind speed of 70 kt for this advisory.

Satellite fixes indicate that Leslie has turned toward the east- northeast and is moving faster at about 10 kt. The track forecast really hinges on whether Leslie gets accelerated in southwesterly flow ahead of an eastern Atlantic trough or gets dropped by that trough and turns southwestward around a new subtropical ridge. Sadly, the forecast agreement from the previous advisory has disintegrated, with all of the GFS-based guidance now indicating a track more toward Europe, while the ECMWF/UKMET send Leslie in the exact opposite direction toward the east-central Atlantic. I clearly drew the small straw in having to make Leslie’s forecast tonight because this situation is resulting in one of the largest guidance spreads I have seen, about 1000 miles on day 3 and over 2000 miles at day 5. Furthermore, the corrected-consensus guidance is closer to the GFS guidance, which is way to the northeast of the previous forecast. The new forecast will somewhat reflect the latest guidance, showing an adjustment to the east, but is still hundreds of miles to the southwest of the latest model consensus. Obviously this is a zero-confidence forecast tonight.

Marginally warm waters and moderate shear could support additional strengthening of Leslie during the next day or two, although the guidance is generally lower than yesterday. By Saturday, colder ocean waters, higher shear and a drier mid-level atmosphere should cause Leslie to weaken. No significant changes were made to the previous intensity forecast. By Monday, Leslie, whether it follows the forecast track or not, will likely be struggling to produce convection or have already transitioned into an extratropical low. Thus the 5 day point shows post-tropical status, perhaps optimistically, but this seems like the most likely option for now.

FORECAST POSITIONS AND MAX WINDS

INIT  11/0300Z 27.9N  41.1W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  11/1200Z 28.4N  39.4W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  12/0000Z 29.9N  35.7W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  12/1200Z 31.3N  30.5W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 48H  13/0000Z 32.3N  25.0W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 72H  14/0000Z 32.0N  20.0W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
 96H  15/0000Z 29.5N  20.5W   35 KT  40 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
120H  16/0000Z 27.5N  25.0W   30 KT  35 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 500 PM AST Wed Oct 10 2018

Hurricane Leslie has held nearly steady since this morning. Recent microwave data indicate that the cyclone still has a fairly well-defined inner-core that has persisted, though the deepest convection has fluctuated since last night. Satellite intensity estimates have fluctuated with the convection, but still support an initial value of 65 kt for this advisory. The last few IR and visible images before sunset suggest that Leslie may be developing a banding eye, and it’s possible the intensity estimate is a little conservative.

The track uncertainty is hopefully beginning to decrease a little. The most recent GFS and ECMWF ensembles are converging on a solution where Leslie accelerates east-northeastward on the south side of a mid-latitude trough, before separating from the trough over the weekend. The cyclone could then turn southward, and eventually back westward as a much weaker tropical cyclone or remnant low. This is generally consistent with previous NHC forecasts, so no large changes were required to the NHC forecast which is heavily based on the HFIP Corrected Consensus.

Leslie is still expected to strengthen soon, and there has been no significant change to the intensity forecast. By 72 h, if not sooner, the hurricane will begin to encounter colder ocean waters and high shear, which should cause it to weaken. If Leslie follows the forecast track, it is possible that the system could become a post-tropical remnant low by early next week, and this is forecast by some of the global models. However, this is not explicitly shown in the NHC forecast and Leslie’s strength and status early next week will likely heavily depend on its track at that time. The official forecast is close to the intensity consensus at all forecast hours, and the intensity model spread is not very large.

FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 27.8N  41.9W   65 KT  75 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  11/0600Z 28.0N  40.8W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  11/1800Z 29.0N  38.0W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  12/0600Z 30.4N  33.6W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 48H  12/1800Z 31.5N  28.4W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 72H  13/1800Z 32.0N  21.0W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
 96H  14/1800Z 30.0N  21.0W   35 KT  40 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)
120H  15/1800Z 27.0N  26.0W   30 KT  35 MPH - Tropical Storm (WSW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 1100 AM AST Wed Oct 10 2018

Hurricane Leslie has continued to get better organized this morning, and several recent microwave overpasses indicate that the hurricane is maintaining a well-defined mid-level eye. However, objective and subjective intensity estimates have not increased, so the intensity has been held at 65 kt. All of the intensity guidance forecasts that Leslie will resume intensifying later today. Given that the hurricane is located in a low shear environment and crossing over the warmest waters it has encountered in days, this seems very likely. No change was made to the intensity forecast through 48 h. Beyond that time, the intensity forecast is still tied to the track forecast, and the farther south and west Leslie remains, the stronger it will likely be. Extratropical transition also can not be ruled out, which would likely result in a higher intensity by day 5 that indicated by the NHC forecast. The official intensity forecast is still close to the model consensus through day 5, but a large range of possibilities exists by that time, from Leslie becoming a weak post-tropical low, to maintaining near hurricane strength.

The spread in the track guidance is still very large and confidence in the track forecast is low. The most recent ECMWF ensemble has a 5-day spread of over 1500 n mi, while the 5-day GFS ensemble spread is over 1300 n mi. Leslie is forecast to slow down today and turn toward the east-northeast. A faster motion in that direction is anticipated by tomorrow as a mid-latitude trough approaches from the northwest. Leslie will then either undergo extratropical transition and lift northward, continue westward and become a remnant low, or separate from the trough and turn back west. The NHC forecast is near the track consensus at all times and no large changes to the forecast were made since the future track of the cyclone has not become more clear.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 27.8N  42.3W   65 KT  75 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 12H  11/0000Z 27.8N  41.6W   70 KT  80 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 24H  11/1200Z 28.4N  39.7W   75 KT  85 MPH - Category 1 (WSW Santa Cruz de Tenerife, Azores)
 36H  12/0000Z 29.6N  36.2W   80 KT  90 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 48H  12/1200Z 30.7N  31.8W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 72H  13/1200Z 31.5N  23.0W   60 KT  70 MPH - Tropical Storm (WSW Funchal, Maderia)
 96H  14/1200Z 29.5N  22.0W   40 KT  45 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)
120H  15/1200Z 27.0N  26.0W   35 KT  40 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 500 AM AST Wed Oct 10 2018

Hurricane Leslie’s Geostationary satellite and microwave images indicate that Leslie has a large and ragged banded eye feature with deep convection most organized over the northern semicircle. Since the Dvorak classifications from TAFB and SAB are unchanged at 4.0/65 kt, the initial wind speed is held at that value. Leslie has another day or two to strengthen while it remains in low wind shear conditions and over marginally warm waters. After that time, an increase in shear and lower SSTs should cause Leslie to weaken. It is possible that Leslie could become a post-tropical cyclone by day 5, but confidence is not high on that occurring. The NHC intensity forecast is largely an update of the previous one and it lies at the high end of the model guidance.

Leslie is now moving southward at 9 kt in the flow on the southwest side of a broad mid- to upper-level trough. A slower south- southeastward motion is expected during the day today as the trough pulls away. A turn to the east-northeast is expected tonight as another trough approaches Leslie from the northwest, and that motion with an increase in forward speed is expected through early this weekend. After that time, the models are coming into better agreement in showing Leslie being left behind and moving southwestward on Sunday and Monday as a ridge builds to its northwest. The NHC track forecast is adjusted southward at days 3 to 5 to be closer to the latest consensus aids. Although the deterministic models are in better agreement this cycle, there is still a lot of spread in the GFS and ECMWF ensemble members and confidence in the track forecast remains fairly low.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 28.6N  42.6W   65 KT  75 MPH - Category 1(WNW Santa Cruz de Tenerife, Azores)
 12H  10/1800Z 28.0N  42.3W   70 KT  80 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 24H  11/0600Z 28.1N  40.9W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 36H  11/1800Z 29.1N  38.3W   80 KT  90 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 48H  12/0600Z 30.5N  34.2W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 72H  13/0600Z 31.5N  25.0W   70 KT  80 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 96H  14/0600Z 30.5N  21.5W   50 KT  60 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)
120H  15/0600Z 28.5N  23.5W   40 KT  45 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 1100 PM AST Tue Oct 09 2018

Hurricane Leslie’s – Satellite and microwave data indicate that Leslie has become a hurricane again, almost exactly a week after it did the first time. A WindSat pass from earlier today showed the development of an eye feature, and with the Dvorak estimates from TAFB and SAB at hurricane strength, the initial wind speed is set to 65 kt. The latest GOES-16 proxy visible imagery suggests that a ragged eye has formed, although the eyewall is open on the southwestern side.

Leslie is atypically intensifying while moving south-southeastward at 8 kt. The hurricane should continue to lose latitude for a day or so then get accelerated east-northeastward by a mid-latitude trough until Friday. After that time, there is a ginormous spread in the model ensembles with Leslie’s final destination ranging from Ireland all the way to missing the trough and turning around to the southwest due to a building eastern Atlantic subtropical ridge. Compared to 12 hours ago, more of the ensemble members are showing Leslie getting left behind, which is also reflected in the latest deterministic runs as well. Something tells me that Leslie has at least one more trick up its sleeve, so the official forecast shows this trend, but is very low confidence.

With fairly low shear and marginally warm waters for the next day or two, there is no reason to expect that Leslie won’t continue to intensify. Model guidance is higher than the last cycle, with the normally conservative ECMWF and GFS models even suggesting that Leslie becomes a category 2 hurricane in a couple of days. Most of the rest of the guidance is lower than those models, but the intensity forecast is shaded in the direction of the ECMWF/GFS, and is higher than the last NHC prediction. After that time, an increase in shear and lower SSTs should cause Leslie to weaken. It is even possible it will become a post-tropical cyclone by day 5, but I’m not going to show that at this time since I was too premature last night in this transition.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z 29.5N  42.6W   65 KT  75 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 12H  10/1200Z 28.4N  42.3W   70 KT  80 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 24H  11/0000Z 28.0N  41.6W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 36H  11/1200Z 28.6N  39.8W   80 KT  90 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 48H  12/0000Z 29.9N  36.4W   80 KT  90 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 72H  13/0000Z 32.2N  27.0W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 96H  14/0000Z 32.0N  21.0W   55 KT  65 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)
120H  15/0000Z 30.0N  22.0W   40 KT  45 MPH - Tropical Storm (WNW Santa Cruz de Tenerife, Azores)

NWS National Hurricane Center Miami FL 500 PM AST Tue Oct 09 2018

Tropical Storm Leslie’s appearance on visible imagery has improved through the afternoon, and multiple microwave overpasses show the development of a small mid-level eye. The intensity has been increased to 60 kt based on an average of the most recent Dvorak classifications from TAFB and SAB. Leslie is moving over warmer waters and the wind shear is expected to be low, so additional strengthening is anticipated and Leslie is forecast to become a hurricane overnight. Given the relatively favorable environment and the recent organization of Leslie’s inner-core, it is possible that Leslie could intensify a little faster than currently indicated by the NHC forecast. Beyond day 2, there is particularly low confidence in the intensity forecast since the track of Leslie is highly uncertain, and the NHC forecast essentially follows the intensity consensus. It is likely that the farther south and west Leslie remains, the stronger it will be.

Unfortunately the track forecast has not become any clearer. Recent GFS and ECMWF ensemble forecasts still indicate that a range of possibilities exist, from Leslie becoming extratropical and heading toward the extreme northeast Atlantic, to Leslie turning back west in a few days and persisting as a tropical cyclone. No large changes were made to the track forecast at this time, since I see no reason to commit to a new solution at this time. The NHC forecast is close to HCCA at all forecast hours, but confidence is low to say the least.

FORECAST POSITIONS AND MAX WINDS

INIT  09/2100Z 30.3N  43.0W   60 KT  70 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
 12H  10/0600Z 29.0N  42.6W   65 KT  75 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 24H  10/1800Z 28.0N  42.2W   70 KT  80 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 36H  11/0600Z 28.1N  41.4W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 48H  11/1800Z 29.2N  38.9W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 72H  12/1800Z 32.0N  29.5W   75 KT  85 MPH - Category 1 (WNW Santa Cruz de Tenerife, Azores)
 96H  13/1800Z 33.0N  22.0W   60 KT  70 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
120H  14/1800Z 31.0N  20.0W   45 KT  50 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 500 PM AST Mon Oct 08 2018

Tropical Storm Leslie – GOES-16 data indicate that Leslie has a small central dense overcast with an inner core trying to form on the last few visible images. Convection has also deepened somewhat, and the overall cloud pattern is becoming more symmetric. All signs point to strengthening and the Dvorak estimates are increasing. So for Leslie’s 50th advisory, the wind speed is raised to 50 kt, near the CIMSS ADT value.

Leslie is moving southeastward at about 12 kt; an unusually fast pace for this direction. The storm is forecast to slow down somewhat and turn toward the south-southeast during the next day or two as the cyclone separates from the mid-latitude flow temporarily and becomes steered by a mid-level ridge over the central Atlantic. Fortunately the ridge isn’t strong enough for Leslie to move westward again, and the models all eject Leslie northeastward because of a deepening trough over the eastern Atlantic. There has been a notable trend southward through 48 hours, and the official forecast follows that idea. The forecast becomes a nightmare at long range, however, with very little agreement on whether Leslie is accelerated ahead of the trough, like the latest FV3GFS, or gets left behind again, like the ECMWF. These differences result in a 1200 mile spread of the historically reliable models by day 5, resulting in a very low confidence forecast. The bulk of the guidance is now indicating that the “left behind” option is becoming more likely, but continuity dictates making forecast changes in smaller chunks. So the official forecast is much slower and farther south at long range, but is well north of the latest model consensus. Further southward adjustments could be required if model trends continue.

Interestingly, model guidance is becoming more certain on Leslie becoming a hurricane again as it moves over warmer (but still marginally warm) waters, into a lighter-shear and higher mid-level humidity enviroment. This makes some sense given that the track is shifting southward and Leslie should finally move over a warmer portion of the subtropical Atlantic that it hasn’t touched yet. Thus the intensity forecast is higher than the previous one, and the corrected-consensus models even suggest category 2 as a peak intensity is possible. By day 5, increasing shear and cooler waters should weaken Leslie, and it could be undergoing extratropical transition at that time.

FORECAST POSITIONS AND MAX WINDS

INIT  08/2100Z 33.8N  45.8W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  09/0600Z 32.5N  44.4W   55 KT  65 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
 24H  09/1800Z 30.6N  43.2W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 36H  10/0600Z 28.9N  42.5W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 48H  10/1800Z 28.2N  41.7W   65 KT  75 MPH - Category 1 (WSW Santa Cruz das Flores, Azores)
 72H  11/1800Z 29.5N  37.0W   75 KT  85 MPH - Category 1 (WNW Santa Cruz das Flores, Azores)
 96H  12/1800Z 33.5N  26.5W   75 KT  85 MPH - Category 1 (WSW Funchal, Maderia)
120H  13/1800Z 37.0N  17.0W   60 KT  70 MPH - Tropical Storm (WSW Lisbon, Portugal)

NWS National Hurricane Center Miami FL 1100 AM AST Mon Oct 08 2018

Tropical Storm Leslie – For the fourth (and hopefully final) time as a tropical or subtropical cyclone, Leslie has crossed 48W. The convective pattern of the tropical storm hasn’t changed significantly over the past several hours, though there is some evidence of a convective band attempting to wrap around the western side of the storm. The initial intensity is still 45 kt, based on a blend of the most recent current intensity estimates from TAFB, SAB, and the UW-CIMSS SATCON.

There has been little change in the intensity forecast. Just about all of the typically reliable intensity models still call for Leslie to gradually strengthen over the next 3 days, despite marginal SSTs. All of the dynamical models call for Leslie to become a hurricane once again by 72 h, but SHIPS and LGEM are a little lower. The official intensity forecast remains near the HCCA and IVCN consensus aids, and calls for Leslie to become a hurricane by the end of the week.

Leslie has continued to move east-southeastward, now at 12 kt, and the global models are in good agreement that this motion will continue through today. After that time, most of the guidance generally shows that Leslie will separate from a mid-latitude trough, causing the tropical storm to turn toward the southeast or south-southeast and slow down. A day or so after that, another mid-latitude trough will approach from the west and cause Leslie to accelerate toward the east-northeast. The timing of Leslie’s acceleration is still very uncertain, and the model spread beyond 72 h remains very high. Until the spread decreases, I don’t feel confident making a big change to the forecast, so the official track forecast has only been slightly tweaked to bring it closer to HCCA and TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 34.6N  47.0W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  09/0000Z 33.6N  45.2W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  09/1200Z 32.0N  43.5W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 36H  10/0000Z 30.2N  42.2W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 48H  10/1200Z 29.1N  41.2W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  11/1200Z 29.5N  37.0W   65 KT  75 MPH - Category 1 (WSW Santa Cruz das Flores, Azores)
 96H  12/1200Z 33.0N  28.0W   70 KT  80 MPH - Category 1 (WSW Ponta Delgada, Azores)
120H  13/1200Z 39.0N  18.0W   65 KT  75 MPH - Category 1 (WSW Lisbon, Portugal)

NWS National Hurricane Center Miami FL 500 AM AST Mon Oct 08 2018

Tropical Storm Leslie – There has not been a lot of change with Leslie overnight. Deep convection is still organized in curved bands near and to the north of the center, but there is some dry air entraining into the western side of the circulation. A blend of the latest satellite intensity estimates supports holding the initial intensity at 45 kt.

Leslie is over cool 24 deg C waters, but it will be headed over slightly warmer waters during the next few days while remaining in low wind shear conditions. Therefore, slow strengthening is expected and most of the intensity models show Leslie reaching hurricane strength once again within the next 3 to 4 days. By the end of the period, cooler waters and an increase in shear could cause some weakening. The NHC intensity forecast is a little higher than the previous one, to trend toward the latest IVCN and HCCA guidance.

Leslie is moving east-southeastward at 11 kt steered by the flow on the south side of a broad mid- to upper-level trough over the north Atlantic. An east-southeast to southeast motion is expected during the next couple of days as the trough passes by to the north of Leslie. After that time, another large-scale trough will approach Leslie from the northwest and that should cause the storm to turn east-northeastward at a faster pace in the 4 to 5 day time frame. The models have come into a better agreement this cycle showing a faster and more northward motion at the end of the period, and the NHC forecast has been adjusted accordingly.

INIT  08/0900Z 35.2N  47.9W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  08/1800Z 34.3N  46.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  09/0600Z 32.9N  44.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  09/1800Z 31.1N  42.4W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 48H  10/0600Z 29.6N  41.3W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  11/0600Z 28.8N  38.3W   65 KT  75 MPH - Category 1 (WSW Santa Cruz das Flores, Azores)
 96H  12/0600Z 31.2N  30.4W   70 KT  80 MPH - Category 1 (WNW Santa Cruz das Flores, Azores)
120H  13/0600Z 36.8N  20.0W   65 KT  75 MPH - Tropical Storm (ENE Ponta Delgada, Azores)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Oct 07 2018

Tropical Storm Leslie – Despite marginal SSTs near 24 deg C, Leslie has persisted with little change in its structure. An average of the UW-CIMSS SATCON and current intensity estimates from TAFB and SAB still supports an initial intensity of 50 kt. Although Leslie is currently located in a low-shear environment, GFS and ECMWF SHIPS diagnostics suggests that mid-level humidities are fairly low, and the cyclone should remain over marginal SSTs for the foreseeable future. All of the intensity guidance forecasts little to no intensity change during the next day or so. However, by 36 h, nearly all of the dynamical models, both global and regional, forecast that Leslie will begin to restrengthen. On the other hand, the statistical-dynamical models do not forecast much change through day 5. The NHC forecast has been adjusted a little higher to keep it close to the intensity consensus, and I can’t rule out that Leslie could become a hurricane again at some point during the coming week.

No large changes were made to the NHC track forecast, but this should not be interpreted as a sign of confidence in the forecast. Leslie is currently moving with an initial motion of east-southeast, or 115/9 kt. The track model spread is high from the very beginning of the forecast, with the GFS and its associated regional models indicating that Leslie will continue on a similar heading for the next several days, while the ECMWF and UKMET forecast that Leslie will slow down and turn soon turn toward the southeast or south-southeast. The track forecast variance stems from differences in how quickly the models show Leslie separating from a mid-level trough to its north, if at all, and by day 5, the GFS and ECMWF solutions vary by about 750 n mi. At this point, I don’t have a good reason to pick one solution over another, and it should be noted that based on the ECMWF ensemble tracks, there is a whole spectrum of possible solutions between these extremes. The NHC track forecast therefore remains near the TVCN and GFEX aids as a course of least regret, but significant changes could be required to future advisories if the track of Leslie becomes more clear.

Large swells generated by Leslie are expected to continue through tonight across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 36.6N  51.4W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  08/0000Z 36.2N  49.7W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  08/1200Z 35.4N  47.3W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  09/0000Z 34.2N  44.5W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  09/1200Z 32.6N  41.7W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  10/1200Z 29.1N  36.6W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  11/1200Z 28.5N  31.9W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  12/1200Z 30.0N  28.0W   55 KT  65 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 500 AM AST Sun Oct 07 2018

Tropical Storm Leslie has not changed much overnight. The storm has several curved bands to the east and north of the center, but a limited amount of deep convection in the southwestern quadrant. The initial intensity is held at 50 kt based on the steady state appearance since the previous ASCAT pass. This estimate is also in fair agreement with the latest Dvorak estimates from TAFB and SAB. Leslie will likely fluctuate in strength during the next several days, but it should remain a tropical storm through the forecast period. Although some weakening is possible during the next day or so due to cool 23 to 24 deg C waters, slight re-strengthening is likely after that time when the system moves back over warmer waters and remains in relatively low wind shear conditions. There could be some increase in shear by the end of the forecast period, however, which could result in slight weakening again. The models are in fairly good agreement, and the NHC intensity forecast is close to the IVCN and HCCA consensus models.

Leslie is moving eastward at 10 kt within the mid-latitude westerly flow on the south side of a broad mid- to upper-level trough. This trough is expected to amplify some, which should cause the storm to move east-southeastward at a faster pace during the next few days. A slight turn back to the east or east-northeast with a decrease in forward speed is likely by the end of the forecast period when the trough weakens. There is a significant amount of spread in the models associated with differences on how fast they expect Leslie to move. In fact, the GFS and ECMWF models are more than 1000 n mi apart by day 5. The NHC track forecast is a little slower than the previous one at the end of the period to come in better agreement with the latest consensus aids. Given the model spread, the confidence in the long-range track forecast is low at this time.

Large swells generated by Leslie are expected to continue through tonight across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 37.2N  52.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  07/1800Z 36.6N  50.3W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  08/0600Z 36.1N  48.0W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  08/1800Z 35.1N  45.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  09/0600Z 33.7N  42.2W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  10/0600Z 30.1N  36.0W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  11/0600Z 28.6N  32.0W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  12/0600Z 29.5N  27.2W   50 KT  60 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 1100 PM AST Sat Oct 06 2018

Tropical Storm Leslie’s – convective organization has changed little since the previous advisory, with a small burst of deep convection having developed just southeast of the center. The intensity remains at 50 kt based on an average of current intensity estimates from TAFB and SAB, which is supported by a partial ASCAT pass that showed several 45-kt surface wind vectors well east of the missed low-level center.

The initial motion estimate is easterly or 095/11 kt. Leslie is forecast to remain embedded in weak mid-latitude west-northwesterly flow for the next few days, which should keep the cyclone moving toward the east-southeast over warmer water. By 72 h and beyond, a stronger shortwave trough is forecast to dig to the west of Leslie, lifting the cyclone out toward the east and northeast. The new NHC forecast track is similar to, but a slower than, the previous advisory track, but not as slow as the consensus models.

Leslie is expected to weaken slightly during the next 36 h as the cyclone entrains some drier air. After that time, however, Leslie is expected to move over warmer waters with SSTs reaching more than 25 deg C by 48 h and beyond while the shear is forecast to remain low. As a result, some modest re-strengthening is forecast on days 2-5. The official intensity forecast closely follows the IVCN intensity consensus model.

Large swells generated by Leslie are expected to continue during the next few days across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

ORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 37.3N  52.9W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  07/1200Z 36.8N  51.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  08/0000Z 36.2N  48.8W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  08/1200Z 35.4N  46.4W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  09/0000Z 34.2N  43.7W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  10/0000Z 30.9N  38.5W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  11/0000Z 28.7N  33.9W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  12/0000Z 29.5N  28.5W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Oct 06 2018

Tropical Storm Leslie’s central convection associated with Leslie has become better organized this morning, with conventional satellite imagery showing a tightly curved band and recent microwave imagery showing a mid-level eye. However, the microwave data also suggests the mid-level eye is located to the southeast of the low-level center. It is also not known whether there is an inner wind maximum associated with this feature. Satellite intensity estimates are mostly in the 45-55 kt range, so the initial intensity remains 50 kt.

The initial motion is now 080/8. Leslie is now in or near the southern edge of the mid-latitude westerlies, and with the assistance of a couple of shortwave troughs, these are expected to push Leslie toward the east and southeast throughout the forecast period. Despite general agreement on the synoptic pattern, there is now a large spread in the guidance toward the end of the forecast period. The ECMWF and UKMET show a more southward turn after 72 h, taking Leslie well south of 30N. The GFS, on the other hand, shows a more eastward motion to the point where by 96 h it is 950 n mi from the UKMET forecast position. The new forecast track compromises between these extremes and lies near the TVCN consensus, with the caveat that the part after 72 h is of low confidence.

Leslie should weaken some during the next 48 h or so as it crosses an area of cooler sea surface temperatures. After that, the track takes the center back over warmer water at the same time when there may be an increase in shear. There is an increased uncertainty in the intensity forecast caused by the track forecast uncertainties. If Leslie moves closer to the GFS track, it will be over cooler water and in stronger shear, while if it moves closer to the UKMET solution it will be over warmer water and lighter shear. Due to to the uncertainty, only minor adjustments are made to the previous intensity forecast. Additional adjustments may be needed later depending on changes in the track forecast.

Large swells generated by Leslie are expected to continue during the next few days across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 37.7N  55.8W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  07/0000Z 37.6N  54.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  07/1200Z 37.3N  51.5W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  08/0000Z 36.6N  49.0W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  08/1200Z 35.7N  46.5W   40 KT  45 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  09/1200Z 33.0N  41.5W   45 KT  50 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  10/1200Z 30.0N  37.0W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  11/1200Z 29.0N  31.0W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 500 PM AST Fri Oct 05 2018

Tropical Storm Leslie is currently maintaining a small central convective feature and an outer convective band in the southeastern semicircle. The various satellite intensity estimates have decreased a little, so the initial intensity is nudged downward to 50 kt. This is still a little above the estimates from TAFB, SAB, and the CIMSS satellite consensus. While no data was available from the inner core, scatterometer overpasses this morning suggests that Leslie has changed little in size since last night.

Leslie has now slowed its forward motion and is starting to turn more eastward, with an initial motion of 030/3. A turn to the east is expected during the next 24 h, followed by a turn toward the east-southeast by 36 h as Leslie encounters the southern edge of the mid-latitude westerlies. A general motion toward the east-southeast or southeast should then continue for the remainder of the forecast period. The latest guidance again shifted southward, and the new forecast track, which is in best agreement with the TVCN consensus model, is shifted to the south of the previous track.

The forecast track again takes Leslie over cooler waters around day 2, into slightly stronger shear around day 3, and over warmer water with decreasing shear around days 4-5. However, the structure of Leslie is not currently conducive for rapid changes in intensity either up or down. Thus, the intensity forecast, which has only minor tweaks from the previous forecast, follows the trend of the previous forecast and the guidance in showing gradual weakening near 48 h, followed by slight intensification near 96-120 h.

Large swells generated by Leslie are expected to continue during the next few days across the eastern coast of the United States, Bermuda, the Bahamas, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 36.2N  58.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  06/0600Z 36.7N  57.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  06/1800Z 36.7N  55.8W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  07/0600Z 36.4N  53.8W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  07/1800Z 35.8N  51.7W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  08/1800Z 34.0N  48.0W   45 KT  50 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
 96H  09/1800Z 31.5N  44.5W   50 KT  60 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
120H  10/1800Z 30.0N  42.0W   55 KT  65 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 1100 AM AST Fri Oct 05 2018

Tropical Storm Leslie’s – The structure of Leslie has changed little since the last advisory, with a cluster of convection just north of the low-level center and a second cluster well to the southeast of the center. The initial intensity is held at 55 kt based mainly on continuity from earlier scatterometer data, but it is possible that this is a little generous. It should be noted that overall, Leslie has lost some organization since this time yesterday due to the disappearance of the eye and an overall decrease in convective banding.

Leslie appears to be slowing its forward speed, with the initial motion now 345/8. A turn to the north and a slower forward speed are expected during the next 12 h, followed by a turn toward the east-southeast by 36 h as Leslie encounters the southern edge of the mid-latitude westerlies. A general motion toward the east-southeast or southeast should then continue for the remainder of the forecast period. As noted in the previous advisory, there has been a southward shift in the guidance, and the new forecast track is again shifted a little to the south of the previous track. However, it lies to the north of the HCCA and TVCN consensus models.

The forecast track takes Leslie over cooler waters around days 2-3, into increasing shear around days 3-4, and over warmer water with decreasing shear around days 4-5. However, the structure of Leslie is not currently conducive for rapid changes in intensity either up or down. Thus, the intensity forecast follows the trend of the previous forecast and the guidance in showing gradual weakening for 48-72 h, followed by slight intensification near 96-120 h.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also increase near the coasts of New England and Atlantic Canada later today. Please consult products from your local weather office as these conditions could cause life- threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 36.2N  58.4W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  06/0000Z 36.8N  58.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  06/1200Z 37.1N  56.9W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  07/0000Z 36.9N  54.9W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  07/1200Z 36.5N  53.0W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  08/1200Z 35.0N  49.5W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  09/1200Z 33.0N  45.5W   50 KT  60 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)
120H  10/1200Z 31.0N  42.5W   50 KT  60 MPH - Tropical Storm (WNW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 500 AM AST Fri Oct 05 2018

Tropical Storm Leslie’s  structure has evolved somewhat just within the past 6 hours. Deep convection has redeveloped near the low-level center, although it is displaced a bit to the north due to some southerly shear. The cyclone’s circulation remains quite large, and earlier ASCAT data indicated that the radius of maximum winds is about 90-100 n mi away from the center. Since there is some inner-core convection again, the initial intensity remains 55 kt based on the ASCAT data.

Leslie has gained some speed and has turned toward the north-northwest, now with an initial motion of 345/12 kt. A general northward motion should continue for the next 12-24 hours, but then Leslie will reach the mid-latitude westerlies and make an abrupt turn toward the east by 36 hours. After that time, Leslie is expected to make some significant eastward progress, although the global models are showing several shortwave troughs in the westerlies imparting a southeastward motion on Leslie by days 4 and 5. In fact, some of the models have shifted significantly southward by the end of the forecast period, leaving the previous official forecast near the northern edge of the guidance envelope. Due to this shift, the new NHC track prediction has been adjusted southward on days 3-5, although it does not yet show as much southward motion as indicated by the normally reliable ECMWF, HCCA, and TVCN multi-model consensus.

Leslie doesn’t appear to have to contend with much shear during the next 3 days or so, but with such a large wind field mixing the ocean around it, marginal sea surface temperatures are likely to keep the intensity steady. By days 3 and 4, an increase in shear could cause some slight weakening. The models are in very good agreement in showing little to any change in Leslie’s intensity during the next 5 days, and that is largely what is indicated in the NHC forecast.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also increase near the coasts of New England and Atlantic Canada later today. Please consult products from your local weather office as these conditions could cause life- threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 35.9N  58.3W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 12H  05/1800Z 36.9N  58.4W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 24H  06/0600Z 37.4N  57.6W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 36H  06/1800Z 37.4N  55.8W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 48H  07/0600Z 37.0N  53.7W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  08/0600Z 35.7N  49.7W   45 KT  50 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  09/0600Z 33.5N  45.5W   45 KT  50 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  10/0600Z 31.5N  42.0W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 500 PM AST Thu Oct 04 2018

Tropical Storm Leslie has changed little in convective structure today. Visible imagery shows occasional appearances of an eye inside an area of central convection, with a complex of outer bands wrapping around this inner feature. Infrared imagery, though, suggests that the convection is relatively shallow. Despite the lack of change in the convective pattern, scatterometer data shows there have been significant changes in the wind structure. The strongest winds are now in a band about 90-100 n mi from the center, with the winds in the inner core being notably weaker. This suggest the possibility that Leslie is trying to undergo an eyewall replacement, albeit one with a very large outer eyewall. Based on the scatterometer data and slightly decreased satellite intensity estimates, the initial intensity is reduced to 60 kt.

There is little change to the intensity forecast philosophy, the intensity forecast guidance, or the intensity forecast. While the vertical shear should remain light through the forecast period, the forecast track takes the center away from 26C sea surface temperatures and over 24-25C temperatures, and this should cause a gradual weakening for the next several days. There are major changes to the initial and forecast wind radii based on the scatterometer data and the analyzed initial size.

The initial motion is 355/10. In the short term, Leslie will be steered northward between a mid-level ridge over the central Atlantic and a mid- to upper-level trough seen in water vapor imagery north of Bermuda. A decrease in forward speed should occur from 24-36 h as the trough moves south and a second ridge develops to the west of the tropical cyclone. Beyond 36 h, Leslie is expected to move eastward to east-southeastward at a faster forward speed along the southern edge of the mid-latitude westerlies. Overall, the new forecast track is close to the previous track through 48 h, then a little north of the old track after that time. However, there is an increased spread in the guidance in both the track and the forward speed near the end of the forecast period, and confidence is decreasing for this part of the forecast.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 33.3N  57.5W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 12H  05/0600Z 34.9N  58.0W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 24H  05/1800Z 36.1N  58.2W   60 KT  70 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 36H  06/0600Z 36.8N  57.5W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 48H  06/1800Z 36.7N  55.9W   55 KT  65 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 72H  07/1800Z 36.0N  52.5W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
 96H  08/1800Z 34.5N  48.5W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)
120H  09/1800Z 32.5N  44.5W   50 KT  60 MPH - Tropical Storm (WSW Santa Cruz das Flores, Azores)

NWS National Hurricane Center Miami FL 1100 AM AST Thu Oct 04 2018

Hurricane Leslie continues to have an inner area of convection near the center, with a larger convective band present about 120 n mi from the center and additional banding in the northwestern quadrant. Since the last advisory, the central convection has become less symmetric and the eye has become less defined. Based on this and the latest satellite intensity estimates, the initial intensity is nudged downward to 65 kt. While the vertical shear should remain light through the forecast period, the forecast track takes the center away from 26C sea surface temperatures and over 24-25C temperatures, and this should cause a gradual weakening for the next several days. Since there is little change in the guidance, the new intensity forecast is again an update of the previous forecast.

The initial motion is now 355/8. In the short term, Leslie will be steered northward with some increase in speed between a mid-level ridge over the central Atlantic and a mid- to upper-level trough seen in water vapor imagery north of Bermuda. A decrease in forward speed should occur from 24-36 h as the trough moves south and a second ridge develops to the west of the tropical cyclone. Beyond 48 h, Leslie is expected to move eastward to east-southeastward at a faster forward speed along the southern edge of the mid-latitude westerlies. The track guidance generally agrees with this scenario, although some spread in both direction and speed appears by 120 h. The new track forecast is similar to the previous forecast and is mostly a blend of the TVCN and HCCA consensus models.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 32.5N  57.2W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 12H  05/0000Z 34.1N  57.6W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 24H  05/1200Z 35.8N  58.1W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  06/0000Z 36.6N  58.1W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  06/1200Z 36.8N  56.8W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  07/1200Z 36.0N  53.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  08/1200Z 35.0N  50.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  09/1200Z 33.5N  47.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Thu Oct 04 2018

Hurricane Leslie has shown no appreciable changes in its structure during the past several hours, and it continues to be a little thin on convection within its eyewall. Another more impressive band of convection extends nearly more than 120 n mi northwest of the center of the ragged eye. The initial intensity remains 70 kt for this advisory, mainly based on a blend of Dvorak CI numbers from TAFB and SAB and an earlier SATCON estimate. Leslie’s center has reached sea surface temperatures of 26 degrees Celsius, and these marginal water temperatures are likely to cause a gradual decrease in the cyclone’s winds during the next several days. The new NHC intensity forecast is mainly just an update to the previous forecast, largely following the HCCA guidance and the ICON intensity consensus.

Leslie continues to move northward, or 350/7 kt, between a shortwave trough south of Nova Scotia and a mid-level ridge over the central Atlantic. This northward motion should continue for the next 36 hours before Leslie becomes trapped between two mid-level highs and is isolated from the mid-latitude westerlies to the north, thus causing its forward motion to nearly stall by 48 hours. By days 3 through 5, Leslie should feel enough influence from the westerlies and an approaching cold front to cause it to move a bit faster toward the east or east-southeast over the north Atlantic. Like the intensity forecast, no major changes were required to the official track forecast, which is merely an update to the previous NHC prediction.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 31.4N  57.1W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 12H  04/1800Z 33.0N  57.3W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 24H  05/0600Z 35.1N  58.0W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 36H  05/1800Z 36.3N  58.3W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  06/0600Z 36.8N  57.7W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  07/0600Z 36.3N  54.6W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  08/0600Z 35.5N  51.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  09/0600Z 34.5N  48.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Wed Oct 03 2018

Hurricane Leslie – The satellite presentation of Leslie has changed little over the past six hours. Leslie continues to have a large ragged eye with periodic intrusions of slightly drier air. The hurricane still has well-defined outflow over the northern semicircle. The initial wind speed is held at 70 kt based on the steady state appearance.

Now that Leslie that has begun its advertised northward turn, it is passing over the cool wake that it presumably created during the past day or so, therefore, little change in strength is expected through this evening. However, some slight strengthening is possible later tonight and Thursday after crossing the cool wake. Gradual weakening then is expected to begin late Thursday when the system reaches cooler waters farther to the north. The NHC intensity forecast is an update of the previous one and near the middle of the guidance envelope.

Satellite images indicate that Leslie is moving northward, and this motion appears to be accelerating. This northward motion is expected to continue through Friday as the hurricane moves in the flow between a shortwave trough to the northwest and a mid-level ridge to its southeast. After that time, an eastward motion is forecast when a second trough approaches Leslie from the north. The latest model guidance has shifted a little to the west in the short term and is slightly slower and farther south at the latter forecast points. The NHC official track forecast has been adjusted accordingly to trend toward this guidance.

Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 29.9N  56.9W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 12H  04/0600Z 30.7N  57.0W   75 KT  85 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 24H  04/1800Z 32.7N  57.0W   75 KT  85 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 36H  05/0600Z 34.7N  57.4W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 48H  05/1800Z 36.1N  57.6W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  06/1800Z 36.8N  56.4W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  07/1800Z 36.7N  53.6W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  08/1800Z 36.0N  49.5W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Wed Oct 03 2018

Hurricane Leslie – Deep convection surrounding the center of Leslie has become better organized overnight, with the development of a ragged eye in infrared satellite images. A 0552 UTC AMSR2 microwave overpass revealed a well-defined low-level eye with a ring of broken convection surrounding it. T-numbers from both TAFB and SAB were 4.0 on the Dvorak scale, therefore the initial intensity has been increased to 65 kt. This makes Leslie the sixth hurricane of the 2018 Atlantic hurricane season.

The hurricane is forecast to remain within favorable environmental conditions consisting of warm water and low vertical wind shear over the next day or two. These conditions should allow for some additional strengthening. After 48 hours, Leslie will be moving over cooler waters, which should induce gradual weakening later in the period.

Leslie has become nearly stationary overnight, and it appears that the cyclone’s equatorward motion has likely come to an end. A shortwave trough to the northwest of the storm and a building ridge to the east, are expected to allow Leslie to begin moving northward by tonight. A northward motion is then expected to continue over the next 2-3 days, but by the weekend Leslie is predicted to turn eastward as a broad trough dips southward over the north Atlantic. The dynamical model guidance is in relatively good agreement on this scenario and the new NHC track forecast is essentially an update of the previous advisory.

Large swells generated by Leslie are expected to increase over the next couple of days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada by the end of the week. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 29.6N  56.9W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 12H  03/1800Z 29.7N  57.0W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 24H  04/0600Z 30.8N  57.0W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 36H  04/1800Z 32.8N  57.1W   75 KT  85 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 48H  05/0600Z 35.0N  57.3W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 72H  06/0600Z 37.1N  56.7W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  07/0600Z 37.0N  53.7W   60 KT  70 MPH - Tropical Stprm (ENE Hidden Beach, Bermuda)
120H  08/0600Z 37.0N  50.5W   55 KT  65 MPH - Tropical Stprm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Tue Oct 02 2018

Tropical Storm Leslie is almost a hurricane. Satellite images indicate that a ring of deep convection now nearly surrounds Leslie’s large ragged eye. A pair of ASCAT passes from this morning showed maximum winds around 55 kt. Based on that data and a blend of the latest Dvorak estimates, the initial intensity is increased to 60 kt. Leslie is expected to remain over relatively warm water and in favorable atmospheric conditions for another day or two, so continued gradual strengthening is forecast during that time period. Based on the improved organization this afternoon and the model guidance, Leslie is forecast to reach hurricane strength tonight or early Wednesday. After a couple of days, the system is expected to move over waters cooler than 26 deg C, and those unfavorable oceanic conditions combined with some increase in shear this weekend should cause a slow weakening trend. The NHC intensity forecast remains between the aggressive statistical-dynamical models and the lower HMON and COAMPS-TC models, but this forecast is a tad higher than the previous one.

The tropical storm is still losing latitude, with the latest initial motion now estimated to be 205/8. This south-southwestward motion is expected to slow down tonight, and Leslie will likely come to a stall on Wednesday in very weak steering currents. After that time, the combination of a shortwave trough to the west and an amplifying mid-level ridge to the southeast should cause Leslie to move northward on Thursday and Friday. A turn to the northeast and then east is forecast to occur by the weekend when the storm moves within the mid-latitude westerlies. The NHC track forecast is nudged to the south and west of the previous one to come into better agreement with the latest guidance.

Large swells generated by Leslie are expected to increase tomorrow and Thursday across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada by the end of the week. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

The initial 34- and 50-kt wind radii have been modified based on the aforementioned ASCAT data.

FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 30.1N  56.4W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 12H  03/0600Z 29.7N  56.6W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 24H  03/1800Z 29.5N  56.8W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 36H  04/0600Z 30.7N  56.8W   75 KT  85 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 48H  04/1800Z 32.6N  56.7W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  05/1800Z 36.3N  56.5W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  06/1800Z 37.2N  54.2W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  07/1800Z 37.0N  51.0W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Tue Oct 02 2018

Tropical Storm Leslie has generally changed little during the past several hours. The storm continues to have a ragged banded eye feature with multiple mesovortices within it. Deep convection is most organized in a curved band that currently wraps from the northeast to southwest quadrant of the storm. The initial intensity is held at 55 kt, which is near the high end of the satellite estimates. Although the storm has not strengthened much during the past day or so, it still has an opportunity to intensify while it moves over slightly higher SSTs and remains in favorable atmospheric conditions during the next day or two. Beyond a couple of days, slow weakening seems likely as Leslie heads over SSTs cooler than 26 deg C and into a slightly drier environment. The NHC intensity forecast is the same as the previous one, and it is in good agreement with the HCCA and IVCN consensus aids. This intensity forecast lies between the aggressive statistical-dynamical models and the lower HMON and COAMPS-TC models that keep Leslie below hurricane strength.

The tropical storm continues to lose latitude, with the latest initial motion estimate being 215/7. A continued slow south to south-southwest motion is forecast during the next 24 hours as the system moves in the flow on the east side of a mid-level high. After that time, the combination of a shortwave trough to the west and an amplifying mid-level ridge to the southeast should cause Leslie to move northward to north-northeastward late this week. By the weekend, the models suggest that Leslie should turn eastward when it moves in the mid-latitude westerlies. The NHC track forecast is nudged to the west to come into better agreement with the latest models.

Large swells generated by Leslie are expected to increase tomorrow and Thursday across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada by the end of the week. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 30.9N  56.1W   55 KT  65 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 12H  03/0000Z 30.1N  56.4W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 24H  03/1200Z 29.8N  56.6W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 36H  04/0000Z 30.5N  56.7W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 48H  04/1200Z 31.9N  56.5W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 72H  05/1200Z 35.9N  56.3W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  06/1200Z 37.6N  54.2W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  07/1200Z 37.3N  50.5W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Tue Oct 02 2018

Tropical Storm Leslie – Infrared and passive microwave satellite imagery indicate that convection has increased and become better organized around the well-defined low-level circulation center. In fact, recent microwave images showed that Leslie has developed a closed, 20- to 25-nmi wide low-level eye. Based on the presence of the distinct low-level eye feature and a Dvorak intensity estimate of T3.5/55 kt from SAB, the cyclone’s intensity has been increased to 55 kt.

The initial motion is southwestward or 220 degrees at a faster forward speed of 6 kt. For the next 24 h or so, Leslie is forecast to move slowly southwestward to south-southwestward, trapped between a deep-layer ridge to the west and a mid- to upper-level low to the east. After possibly becoming stationary near the 36-h period, a ridge to the southeast and east of Leslie is forecast to become highly amplified, forcing the cyclone northward into the higher latitudes through 72 h. On days 4 and 5, an approaching mid-latitude shortwave trough well to the north of Leslie is forecast to nudge the cyclone eastward, but only slowly at forward speeds of less than 10 kt. The new NHC forecast track has again been adjusted to the left of the previous advisory track in the 36- to 72-h period, and is similar to but slightly east of the various consensus models.

Leslie’s outflow pattern has become a little more symmetrical during the past 6 h, and further improvement is expected through 72 hours. In addition, lightning data and satellite imagery during the past few hours indicate that convection has been developing in the dry slot to the north and east of the main convective band, suggesting the mid-level environment is finally beginning to moisten. This dry intrusion has been hindering the development of deep eyewall convection and, thus, the lack of intensification of the cyclone. However, given the strong instability that is forecast to develop in the inner-core region region due to very cold air aloft moving over relatively warm waters of near 26C beneath the cyclone, along with increasing outflow and mid-level moisture, slow but steady strengthening seems reasonable for the next 48 hours or so. By 72 h and beyond, gradual weakening is expected as Leslie moves back over cooler oceanic temperatures and dry mid-level air from the mid-latitudes associated with the aforementioned shortwave trough once again gets entrained into the cyclone’s circulation. The official intensity forecast is just an update of the previous advisory, and is similar to the weaker IVCN consensus model.

Large swells generated by Leslie will continue to affect portions of the southeastern coast of the United States, Bermuda, and the Bahamas. These swells could cause life-threatening surf and rip currents. Although the swells are forecast to abate temporarily in the Bahamas later today, they are expected to increase again on Wednesday and Thursday, and propagate farther southward into the Greater and Lesser Antilles. Please consult products from your local weather office.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 31.6N  55.6W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  02/1800Z 30.6N  56.1W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  03/0600Z 29.9N  56.5W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 36H  03/1800Z 30.2N  56.6W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 48H  04/0600Z 31.3N  56.4W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  05/0600Z 35.0N  56.3W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  06/0600Z 37.1N  54.8W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda))
120H  07/0600Z 37.1N  51.9W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Mon Oct 01 2018

Tropical Storm Leslie – The cloud pattern of Leslie has improved throughout the day, and the system now has a ragged eye with multiple mesovorticies within it. In addition, the associated convection has become more symmetric this afternoon, but the cloud tops are not very cold south of the center. Even though the system looks better organized, the satellite intensity estimates are again unchanged. Accordingly, the initial intensity is held at 50 kt near the high end of the satellite estimates.

Leslie will likely strengthen gradually during the next day or so as it heads toward slightly warmer SSTs and remains in relatively low wind shear conditions. Most of the models show Leslie becoming a hurricane on Tuesday, and the NHC forecast follows that guidance. Leslie is expected to move north-northeastward back over its own upwelled cool waters late this week and this weekend, which should promote a gradual weakening trend. The NHC intensity forecast is identical to the previous one and in line with the HCCA and IVCN models.

Leslie continues to drift to the southwest on the east side of a mid-level high. There has been no change to the track forecast philosophy. Leslie is expected to continue to move slowly southward to southwestward in weak steering currents during the next couple of days. Thereafter, a developing shortwave trough to the west of Leslie should cause it to move north-northeastward to northeastward at a slightly faster pace. The guidance has shifted south and west this cycle, and the NHC track forecast has been adjusted in those directions. Regardless of the details of the forecast track, there is high confidence that Leslie will meander for quite a while over the central Atlantic.

Large swells generated by Leslie will continue to affect portions of the southeastern coast of the United States, Bermuda, the Bahamas, and most of the Greater and Lesser Antilles through tonight. These swells could cause life-threatening surf and rip currents. Although the swells will diminish slightly by Tuesday, they are expected to increase again over the Bahamas and most of the Greater and Lesser Antilles late Wednesday and Thursday.

 

FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 32.8N  54.6W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  02/0600Z 31.9N  55.4W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  02/1800Z 30.9N  55.9W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 36H  03/0600Z 30.2N  56.2W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 48H  03/1800Z 30.0N  56.4W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  04/1800Z 33.3N  55.8W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  05/1800Z 36.4N  55.0W   60 KT  70 MPH - Tropical Storm (ESE Shelburne, Nova Scotia)
120H  06/1800Z 37.2N  52.8W   60 KT  70 MPH - Tropical Storm (ESE Shelburne, Nova Scotia)

NWS National Hurricane Center Miami FL 1100 AM AST Mon Oct 01 2018

Tropical Storm Leslie is gradually becoming better organized. A large band of deep convection exists on the west side of the circulation and some fragmented bands are beginning to form on the east side. Overall, Leslie appears more symmetric than it has been during the past couple of days due to a decrease in wind shear. Despite the improved appearance, the satellite intensity estimates are largely unchanged, so the initial intensity is held at 50 kt, near the high end of the estimates.

Since Leslie is forecast to be in a low wind shear environment and expected to move over slightly higher SSTs during the next couple of days, slow strengthening is predicted. Most of the models show Leslie becoming a hurricane in 24 to 36 hours, and the NHC forecast follows suit. By late in the week and this weekend, Leslie is expected to move north-northeastward back over its previous track, where it has upwelled cooler waters. These less conducive oceanic conditions should cause a slow decay.

Leslie continues to drift to the southwest on the east side of a mid-level high, and a continued slow south to southwest motion is expected during the next couple of days. Thereafter, a developing shortwave trough to the west of Leslie should cause it to move north-northeastward but only at a slightly faster pace. The NHC track forecast is nudged to the left of the previous one to come into better agreement with the latest guidance. Regardless of the details of the forecast track, there is high confidence that Leslie will meander for quite a while over the central Atlantic.

Large swells generated by Leslie will continue to affect portions of the southeastern coast of the United States, Bermuda, the Bahamas, and most of the Greater and Lesser Antilles through tonight. These swells could cause life-threatening surf and rip currents. Although the swells will diminish slightly by Tuesday, they are expected to increase again over the Bahamas and most of the Greater and Lesser Antilles late Wednesday and Thursday.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 33.2N  54.3W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  02/0000Z 32.7N  54.9W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  02/1200Z 31.6N  55.6W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 36H  03/0000Z 30.7N  55.9W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 48H  03/1200Z 30.4N  56.0W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  04/1200Z 32.5N  55.3W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  05/1200Z 35.7N  54.4W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  06/1200Z 37.4N  52.0W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Mon Oct 01 2018

Tropical Storm Leslie has become a little better organized overnight, with an increase in convective banding over the northern and northwestern portions of the circulation. ASCAT data around 0000 UTC revealed 40-45 kt winds over the northeastern quadrant of the cyclone and with the increase in organization since that time, the initial intensity has been raised to 50 kt. This is a little above the consensus Dvorak intensity estimates of T3.0 (45 kt) from TAFB and SAB. The shear that was affecting Leslie appears to have abated somewhat and with the system forecast to move southwestward toward slightly warmer waters, gradual strengthening is expected during the next couple of days. Later in the period, Leslie is forecast to move north-northeastward back over its previous track where cooler upwelled waters are likely to produce some weakening. The updated NHC intensity forecast shows a slightly higher peak intensity in 48 to 72 hours, but remains between the dynamical model guidance and the higher statistical models.

Leslie continues to plod along with an initial motion estimate of 240/4 kt. The cyclone should move slowly southwestward to southward during the next couple of days as it remains within an area of weak steering currents. After that time, a shortwave trough to the northwest of Leslie is expected to allow the tropical cyclone to lift slowly north-northeastward by days 4 and 5. Although the dynamical model guidance is in agreement on this overall scenario, there is increasing cross-track (east-west) spread after 72 hours. The latest run of the ECMWF has shifted westward and brackets the western edge of the guidance envelope. The new NHC track forecast has been shifted in that direction, but it is not as far left as the various consensus aids out of respect of the previous track forecast. Regardless of the details of the forecast track, Leslie is still expected to meander over the central Atlantic through the remainder of this week.

Large swells generated by Leslie when it was a strong extratropical low will continue to affect portions of the southeastern coast of the United States, Bermuda, the Bahamas, and most of the Greater and Lesser Antilles for another day or two. These swells could cause life-threatening surf and rip currents. Although the swells will diminish some by mid-week, they will likely remain hazardous for the same locations through the forecast period due to Leslie’s slow motion.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 33.4N  53.9W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  01/1800Z 33.1N  54.5W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  02/0600Z 32.2N  55.3W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  02/1800Z 31.2N  55.8W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 48H  03/0600Z 30.6N  56.0W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 72H  04/0600Z 31.7N  55.2W   70 KT  80 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  05/0600Z 35.0N  54.3W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
120H  06/0600Z 37.4N  52.0W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Sun Sep 30 2018

Tropical Storm Leslie has generally changed little in organization today. The tropical storm continues to produce deep convection in a band to the southeast of the center, but there is a minimal amount of shower activity elsewhere. This asymmetric cloud pattern is due to about 25 kt of northwesterly wind shear. The initial intensity is again held at 45 kt, but some of the satellite estimates suggest that this could be a little generous. The global models show the upper-level pattern becoming more favorable over Leslie in about a day, which combined with warmer SSTs should allow Leslie to gradually strengthen during the next 2 to 3 days. After that time, the storm is expected to move northeastward back over its previous track and cooler waters partly caused by its own upwelling. These conditions should end the strengthening trend and induce some weakening. The NHC intensity forecast is largely an update of the previous one and in line with the IVCN, FSSE, and HCCA consensus models.

Leslie is drifting to the southwest, with the latest initial motion estimate being 240/4 kt. The storm is forecast to remain in very weak steering currents, and Leslie will likely drift southward to southwestward during the next few days on the east side of a mid-level ridge. Thereafter, a developing trough to the southwest of Leslie should cause the system to move northeastward at a slightly faster pace. The models continue to shift back and forth each cycle, which is not surprising given the weak steering. This forecast is adjusted a little to the left of the previous one to come into better agreement with the latest models. The bottom line is that Leslie is forecast to meander over the central Atlantic for the next several days.

Large swells generated by Leslie when it was a strong extratropical low will continue to affect the east coast of the United States and most of the Greater and Lesser Antilles for another day or two. These swells could cause life-threatening surf and rip currents. Although the swells will diminish some by mid-week, they will likely remain hazardous for the same locations through the forecast period due to Leslie’s slow motion.

FORECAST POSITIONS AND MAX WINDS

INIT  30/2100Z 33.5N  53.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  01/0600Z 33.3N  53.7W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  01/1800Z 32.9N  54.3W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  02/0600Z 32.1N  55.0W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 48H  02/1800Z 31.3N  55.3W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 72H  03/1800Z 31.0N  54.7W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
 96H  04/1800Z 33.5N  53.5W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  05/1800Z 36.5N  52.0W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Sep 30 2018

Tropical Storm Leslie – Deep convection has increased a little during the past several hours in a band to the southeast of the center, but the shower activity remains quite limited elsewhere in the circulation. The latest satellite intensity estimates and a recent ASCAT pass still support an initial intensity of 45 kt. Leslie is expected to be moving into a lower wind shear environment and over warmer SSTs during the next few days. These conditions should support some gradual strengthening during that time period. After that time, however, Leslie is expected to move over cooler waters, partly induced by its own upwelling, as it heads northeastward back over its previous track. Accordingly, slight weakening is shown toward the end of the forecast period. The NHC intensity forecast is similar to the previous one and generally follows the consensus models, IVCN and HCCA.

Leslie is drifting to the southwest, with the latest initial motion estimate being 230/3 kt. Leslie is caught in very weak steering currents, and a continued slow southwest to south motion is expected during the next few days. Thereafter, the models show a weak trough developing to the southwest of Leslie and that should cause the system to move northeastward at a slightly faster pace. The models have trended a little to the east this cycle, and the NHC forecast has been adjusted in that direction. The bottom line is that Leslie is forecast to meander over the central Atlantic through the forecast period.

Large swells generated by Leslie when it was a strong extratropical low will continue to affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles for another day or two. These swells could cause life-threatening surf and rip currents. Although the swells will diminish some by mid-week, they will likely remain hazardous for the same locations through the forecast period due to Leslie’s slow motion.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 33.6N  52.6W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  01/0000Z 33.2N  53.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  01/1200Z 32.9N  53.6W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  02/0000Z 32.3N  54.0W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  02/1200Z 31.6N  54.3W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  03/1200Z 30.8N  54.2W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  04/1200Z 33.0N  52.5W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
120H  05/1200Z 36.0N  51.5W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Sun Sep 30 2018

Tropical Storm Leslie – Convection associated with the tropical storm has become more fragmented over the past 12 hours or so, and now consists of several broken bands primarily over the southeastern portion of the circulation. Satellite intensity estimates have not changed much since the previous advisory, and the initial intensity is held at 45 kt, which is in agreement with earlier ASCAT data and a recent UW/CIMSS SATCON estimate of 42 kt. The recent warming of the clouds tops may be associated with cooler waters caused by upwelling beneath the large, slow-moving tropical storm. Leslie, however is forecast to move southwestward toward somewhat warmer waters and a more favorable upper-level environment during the next 2 to 3 days. This conditions should allow for gradual strengthening, and the NHC forecast follows the intensity guidance by bringing Leslie to hurricane strength in about 72 hours. Later in the period, Leslie is likely to move back over some of the cooler upwelled waters along its previous track, which could result in gradual weakening.

Recent satellite fixes show that Leslie is moving west- southwestward or 240 degrees at 4 kt. The tropical storm is caught between a pair of mid-level ridges and a slow southwestward to south-southwestward motion is expected over the next 2 to 3 days. Around mid-week, a shortwave trough moving off the coast of the northeastern United States is expected to help lift Leslie slowly northward at days 4 and 5, but the models have trended toward a somewhat slower solution. Despite the storm’s expected slow motion, the spread in the track guidance becomes fairly large by days 4 and 5, and it appears that Leslie is likely to meander over the Central Atlantic for quite some time.

Large swells generated by Leslie when it was a strong extratropical low will affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles through at least the early part of this week. These swells could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 33.8N  52.5W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  30/1800Z 33.4N  53.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  01/0600Z 32.9N  53.8W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  01/1800Z 32.5N  54.2W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  02/0600Z 31.9N  54.5W   55 KT  65 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 72H  03/0600Z 30.7N  54.7W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
 96H  04/0600Z 32.4N  54.1W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)
120H  05/0600Z 35.5N  53.0W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Sat Sep 29 2018

Tropical Storm Leslie has continued to take on more tropical characteristics over the past few hours. Anti-cyclonic outflow is now present to the northeast and southeast of Leslie and its primary convective band. Late-arriving AMSU data from 1316 UTC also indicated that Leslie has developed a deep-layer warm core structure. Based on these factors, Leslie has been designated as a tropical storm. The initial intensity is set at 45 kt, based on a blend of recent satellite intensity estimates from TAFB and the UW-CIMSS SATCON.

Leslie continues to move slowly southwestward with an initial motion of 225/5 kt. The guidance is in very good agreement that this general motion will continue for another 24 h or so, before the cyclone becomes nearly stationary by early next week. An approaching mid-latitude trough is still expected to eventually cause Leslie to turn toward the north or northeast, perhaps over its own track, in 4 or 5 days. Only minor adjustments were made to the NHC track forecast, which remains close to the various track consensus aids.

The NHC intensity forecast has not been changed in any significant way and remains near the intensity consensus, but slightly favors the regional hurricane models. Leslie is currently located over fairly cool SSTs, and its slow motion could cause further ocean cooling. This could particularly be an issue in a few days when the tropical storm is expected to become nearly stationary. The ocean-coupled regional models (HWRF, HMON, COAMPS-TC) continue to indicate that Leslie will struggle to intensify much over the next few days, despite a fairly favorable upper-level environment. On the other hand, some of the uncoupled global models and the SHIPS and LGEM models suggest that more intensification will occur and that Leslie could become a hurricane in a few days. Highlighting the potential importance of SSTs in this case, the SHIPS and LGEM models began using daily SST fields at 18Z, which show nearly 2 deg C cooler SSTs along the track of Leslie, and those models now show much less intensification than they did before.

Large swells generated by Leslie when it was a strong extratropical low will affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles through the weekend. These swells could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 34.1N  51.3W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  30/0600Z 33.6N  52.0W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  30/1800Z 33.1N  53.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  01/0600Z 32.8N  53.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  01/1800Z 32.5N  53.9W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  02/1800Z 31.5N  54.7W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  03/1800Z 31.5N  54.5W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
120H  04/1800Z 34.0N  54.0W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 29 2018

Tropical Storm Leslie cloud pattern has taken on a more tropical appearance since last night. However, the cyclone is still co-located with an upper-level low, so its status as a subtropical cyclone is maintained for this advisory. The initial intensity remains 40 kt, based on a subtropical classification of 35-40 kt from TAFB.

The global models forecast that Leslie will separate from the upper-level low over the course of the next day or so, which should complete its transition to a tropical cyclone. While this could result in a short-term increase in shear over Leslie, by early next week the cyclone will likely be located within a fairly low shear environment. However, Leslie is expected to move very slowly by that time, and ocean upwelling could limit or prevent further strengthening. There is a large amount of spread in the intensity guidance by day 5, but it is worth noting that the models most capable of properly representing the effect of ocean cooling on intensity, COAMPS-TC, HWRF, and HMON, all keep Leslie below hurricane strength for the next 5 days. The HWRF in particular forecasts nearly 5 deg C of ocean cooling beneath the cyclone. The NHC intensity forecast is generally a little lower than the previous advisory, but is still near the IVCN and HCCA consensus aids at all forecast hours. If Leslie moves more than expected, it would not be surprising if it strengthened more than currently forecast.

Little change was made to the official track forecast. Leslie is still expected to move slowly southwestward for the next couple of days, before coming to a near halt early next week. By the middle of the week, an approaching mid-latitude trough could steer Leslie toward the north or northeast and allow the cyclone to start gaining speed, however, there is a lot of spread among the global models as to how quickly this will occur, and confidence in this portion of the forecast is fairly low.

Large swells generated by Leslie when it was a strong extratropical low will affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles through the weekend. These swells could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 34.4N  50.8W   40 KT  45 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  30/0000Z 33.8N  51.7W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  30/1200Z 33.3N  52.7W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  01/0000Z 33.1N  53.5W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  01/1200Z 32.8N  54.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  02/1200Z 31.6N  55.0W   55 KT  65 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
 96H  03/1200Z 31.0N  55.5W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
120H  04/1200Z 33.0N  55.0W   65 KT  75 MPH - Category 1 (ENE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Sat Sep 29 2018

Tropical Storm Leslie – The deep convection has become more concentrated near the center during the past several hours indicating that Leslie is gradually acquiring some tropical characteristics, but the cyclone is still too attached to a complex deep-layer low. On this basis, Leslie is still considered a subtropical storm in this advisory with an initial intensity of 40 kt. Global models indicate that the subtropical cyclone will continue to be embedded within strong northerly shear during the next 2 days or so. After that time, the shear is forecast to relax and with a warm ocean along the cyclone’s path, Leslie is forecast to become fully tropical and reach hurricane status by the end of the forecast period. SHIPS model and its derivatives strengthen Leslie significantly, but the NHC forecast is a little less aggressive, and it follows the intensity consensus.

Leslie has been moving toward the southwest or 230 degrees at 6 kt, steered by the flow around the western side of the large deep-layer low in which Leslie is embedded. Since this steering pattern is not expected to change, Leslie will probably continue on the same general track for the next 3 to 4 days. After that time, the large low weakens and the cyclone will become steered slowly northward by the flow ahead of an approaching mid-latitude trough. Nevertheless, Leslie is forecast to meander over the north-central Atlantic for several more days. This is the solution provided by most of the global models, and the NHC forecast follows very closely the multi-model consensus aids and the corrected consensus HCCA.

Large swells previously generated by Leslie when it was a stronger extratropical low have already reached Bermuda, and will soon reach the Lesser and Greater Antilles. These swells are expected to reach portions of the east coast of the United States by Sunday. These swells could cause life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 35.2N  50.3W   40 KT  45 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  29/1800Z 34.4N  51.3W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  30/0600Z 33.8N  52.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  30/1800Z 33.5N  53.3W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  01/0600Z 33.2N  54.0W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  02/0600Z 32.3N  55.0W   60 KT  70 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  03/0600Z 31.0N  55.5W   65 KT  75 MPH - Category 1 (ESE Hidden Beach, Bermuda)
120H  04/0600Z 32.0N  56.0W   70 KT  80 MPH - Category 1 (ESE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Sat Sep 29 2018

The deep convection has become more concentrated near the center during the past several hours indicating that Leslie is gradually acquiring some tropical characteristics, but the cyclone is still too attached to a complex deep-layer low. On this basis, Leslie is still considered a subtropical storm in this advisory with an initial intensity of 40 kt. Global models indicate that the subtropical cyclone will continue to be embedded within strong northerly shear during the next 2 days or so. After that time, the shear is forecast to relax and with a warm ocean along the cyclone’s path, Leslie is forecast to become fully tropical and reach hurricane status by the end of the forecast period. SHIPS model and its derivatives strengthen Leslie significantly, but the NHC forecast is a little less aggressive, and it follows the intensity consensus. Leslie has been moving toward the southwest or 230 degrees at 6 kt, steered by the flow around the western side of the large deep-layer low in which Leslie is embedded. Since this steering pattern is not expected to change, Leslie will probably continue on the same general track for the next 3 to 4 days. After that time, the large low weakens and the cyclone will become steered slowly northward by the flow ahead of an approaching mid-latitude trough. Nevertheless, Leslie is forecast to meander over the north-central Atlantic for several more days. This is the solution provided by most of the global models, and the NHC forecast follows very closely the multi-model consensus aids and the corrected consensus HCCA. Large swells previously generated by Leslie when it was a stronger extratropical low have already reached Bermuda, and will soon reach the Lesser and Greater Antilles. These swells are expected to reach portions of the east coast of the United States by Sunday. These swells could cause life-threatening surf and rip currents.

NWS National Hurricane Center Miami FL 500 PM AST Fri Sep 28 2018

Central convection associated with Post-Tropical Storm Leslie  has gradually increased during the last couple of days and is now organized into a group of bands that wraps most of the way around the center. In addition, scatterometer data show that the cyclone has lost much of its large baroclinic wind field, and that the radius of maximum winds has contracted from 120-180 n mi yesterday to 90 n mi or less today. While the storm has also developed a warm core and shed some of its baroclinic characteristics, it is embedded in a large deep-layer low pressure system, and thus it is designated subtropical instead of tropical. The initial intensity is set at 45 kt based on the scatterometer data.

Leslie has been moving generally westward for the the past few days. The large-scale models forecast a general southwesterly motion for the next 3-4 days as the cyclone is steered by a segment of the subtropical ridge to its west and another large deep-layer low forming to its east over the eastern Atlantic, with a decrease in forward speed near the end of the forecast period as the ridge to the west weakens. The forecast guidance is tightly clustered through 120 h, and the forecast track is near the center of the guidance envelope and the consensus models.

The forecast track takes the center of Leslie over increasing sea surface temperatures during the next several days, although the temperatures may not be as warm as those indicated in the SHIPS model. The global models suggest that little change in strength will occur during the first 48-72 h as Leslie gradually develops the upper-level outflow pattern of a tropical cyclone and transitions to a tropical storm. After that time, they are in good agreement that the cyclone will strengthen. Based on this, the intensity forecast shows only modest intensification during the first 48 h, followed by strengthening to a probably conservative 60 kt. The forecast also calls for transition to a tropical storm between 48-72 h, with the caveat that this could occur earlier.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 36.1N  48.1W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 12H  29/0600Z 35.4N  49.6W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 24H  29/1800Z 34.4N  51.2W   45 KT  50 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 36H  30/0600Z 33.8N  52.2W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 48H  30/1800Z 33.2N  53.1W   50 KT  60 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 72H  01/1800Z 32.5N  54.5W   55 KT  65 MPH - Tropical Storm (ENE Hidden Beach, Bermuda)
 96H  02/1800Z 31.0N  56.0W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)
120H  03/1800Z 31.0N  57.0W   60 KT  70 MPH - Tropical Storm (ESE Hidden Beach, Bermuda)

NWS National Hurricane Center Miami FL 200 PM EDT Fri Sep 28 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical Storm Kirk, located over the eastern Caribbean Sea. Post-Tropical Cyclone Leslie  is located over the central Atlantic Ocean about 1000 miles west of the Azores.

The associated shower activity is becoming better organized, and recent satellite wind data indicates that the circulation has become more characteristic of a subtropical cyclone. If current trends continue, advisories will be re-initiated later today or tonight. Regardless of whether the system becomes a subtropical or tropical cyclone, Leslie should continue to produce strong winds and high seas over a large portion of the central Atlantic for the next several days. For more information on this system, see High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…high…near 100 percent. * Formation chance through 5 days…high…near 100 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Fri Sep 28 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Kirk, located over the eastern Caribbean Sea.

Post-Tropical Cyclone Leslie is located over the central Atlantic Ocean, several hundred miles west of the Azores. Shower activity has gradually increased near the center of the cyclone since last night and Leslie is expected to once again become a subtropical storm later today or tomorrow. Earlier satellite data indicated that the powerful low is producing storm-force winds that extend several hundred miles from the center, and Leslie will likely continue producing strong winds and high seas over a large portion of the central Atlantic for the next few days regardless of when it completes its transition to a subtropical storm. For more information on this system, see High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Thu Sep 27 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Kirk, which is approaching the Lesser Antilles.

Post-Tropical Cyclone Leslie,  located over the central Atlantic Ocean several hundred miles west of the Azores, remains a powerful non-tropical low with storm-force winds. The associated shower activity is gradually becoming better organized, and Leslie is expected to again become a subtropical storm, or possibly a tropical storm, tonight or Friday while it moves west-southwestward at about 10 mph over the north-central Atlantic. For more information on this system, see High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high...90 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Thu Sep 27 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Kirk, located a couple of hundred miles east of the Lesser Antilles.

Post-Tropical Cyclone Leslie, located over the central Atlantic Ocean several hundred miles west of the Azores, remains a powerful non-tropical low with hurricane-force winds. The associated shower activity is gradually becoming more organized, and Leslie is expected to again become a subtropical storm, or possibly a tropical storm, later today or Friday while it moves west-southwestward at about 10 mph over the north-central Atlantic. For more information on this system, see High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Wed Sep 26 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical Storm Kirk, located a few hundred miles east of the Lesser Antilles.

Post-Tropical Cyclone Leslie  located several hundred miles west-southwest of the Azores is producing disorganized shower activity and gale-force winds. Leslie is expected to reacquire subtropical or tropical characteristics on Thursday or Friday while the cyclone meanders over the north-central Atlantic. For more information on this system, see High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Wed Sep 26 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center has re-initiated advisories on Tropical Storm Kirk, located a few hundred miles east of the Windward Islands.

Post-Tropical Cyclone Leslie located several hundred miles west-southwest of the Azores is producing disorganized shower activity and gale-force winds. Leslie is expected to reacquire subtropical or tropical characteristics on Thursday or Friday while the cyclone meanders over the north-central Atlantic. For more information on this system, see High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 200 AM EDT Wed Sep 26 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

Post-Tropical Cyclone Leslie  centered about 850 miles west-southwest of the Azores is producing disorganized shower activity and gale-force winds. Leslie is expected to reacquire subtropical or tropical characteristics on Thursday or Friday while the cyclone meanders over the north-central Atlantic. For more information on this system, see High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...90 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Tue Sep 25 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

Post-Tropical Cyclone Leslie  is currently centered about 950 miles southwest of the Azores Islands, and it is forecast to meander over the central Atlantic for the next day or so. By Thursday or Friday, Leslie is expected to reacquire subtropical or tropical characteristics while the cyclone moves slowly eastward to east-northeastward over the north-central Atlantic. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 1100 AM AST Tue Sep 25 2018

Subtropical Storm Leslie –   has become a post-tropical cyclone. Conventional and microwave satellite imagery show that Leslie’s surface circulation has become elongated along an intruding baroclinic zone indicated by a recent 1158 UTC ASCAT-A pass. Any deep convection appears to be developing due to dynamic forcing. A rather large stratocumulus cloud shield and associated cooler, stable air is quickly advecting into the area as well. The initial intensity is maintained at 30 kt for this last advisory.

Leslie is forecast to strengthen during the next couple of days due to baroclinic processes. The official forecast, based on the GFS and European global models, and the SHIPS statistical intensity guidance, shows an increase of the sustained winds to hurricane force in 2 days, around the same period that the shear drops below 10 kt. The non-tropical low is then forecast to move south of the strong upper-level westerlies and detach from the frontal boundary. According to the global models and the Florida State Cyclone Phase forecast, Leslie should make a transition from a frontal system to an asymmetric shallow warm-core seclusion. Beyond day 3, guidance suggests that Leslie will acquire subtropical characteristics and a more symmetric, deepening warm-core low while meandering in weaker steering currents. The intensity forecast follows this scenario and is based on the aforementioned global and statistical models.

Leslie is now moving eastward at a slightly faster forward motion, about 10 kt. A turn to the north is expected in 36 hours followed by a slower westward motion as Leslie slips south of the mid-latitude westerlies. Through the remaining portion of the forecast, Leslie should move at a slower speed generally westward as a ridge builds to the north. NHC forecast is nudged toward the TVCN consensus through 48 hours, then follows more closely to the GFEX (GFS/ECMWF) consensus model.

This is the last advisory issued by the National Hurricane Center on Leslie.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 31.6N  44.4W   30 KT  35 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
 12H  26/0000Z 32.1N  42.5W   40 KT  45 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
 24H  26/1200Z 33.6N  40.1W   50 KT  60 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
 36H  27/0000Z 35.6N  39.9W   60 KT  70 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
 48H  27/1200Z 36.1N  41.7W   65 KT  75 MPH - Postropical Storm (ENE St. Georges,  Bermuda)
 72H  28/1200Z 35.5N  45.3W   60 KT  70 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
 96H  29/1200Z 34.6N  48.1W   55 KT  65 MPH - Subtropical Storm (ENE St. Georges,  Bermuda)
120H  30/1200Z 34.4N  49.6W   50 KT  60 MPH - Subtropical Storm (WSW Ponta Delgada, Azores)

NWS National Hurricane Center Miami FL 800 AM EDT Tue Sep 25 2018

 Subtropical Depression Leslie is forecast to become post-tropical today after it merges with a cold front over the central Atlantic. After that time, Leslie is expected to reacquire subtropical or tropical characteristics by the end of the week as it meanders over the central Atlantic. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…high...70 percent.

NWS National Hurricane Center Miami FL AL132018 1100 AM AST Mon Sep 24 2018

Conventional satellite imagery shows little change in Leslie’s cloud pattern during the past several hours with the exception of a few new isolated thunderstorms developing near the surface center. Accordingly, the initial intensity for this advisory is kept at 35 kt. The statistical intensity guidance and the large-scale models show Leslie commencing a strengthening trend in 24 hours as a mid-latitude baroclinic system digs southeastward toward the cyclone. Some of the models also indicate that Leslie, after completing an extratropical transition in around 48 hours, will deepen and generate a large area of gale force winds, particularly in the northwest quadrant. The NHC intensity forecast reflects this scenario and is just below the IVCN intensity consensus.

The initial motion is estimated to be an eastward drift, or 090/4 kt within the increasing mid-level westerly steering flow. A turn to the east-northeast is forecast as an approaching mid-latitude trough and associated cold front approaches from the northwest over the central Atlantic. The deterministic guidance indicate that the aforementioned baroclinic system will overtake Leslie near the 48 hour period, and influence a transition to a non-tropical low pressure system. Subsequently, the GFS and the European models still show extratropical Leslie as the primary system and deepening with time. For now, the official forecast will indicate a merging scenario, but succeeding advisories may include extratropical low forecast points through day 5.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 32.5N  48.0W   35 KT  40 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 12H  25/0000Z 32.5N  47.2W   35 KT  40 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 24H  25/1200Z 32.4N  45.5W   40 KT  45 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 36H  26/0000Z 32.3N  42.8W   45 KT  50 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 48H  26/1200Z 33.6N  39.9W   50 KT  60 MPH - Tropical Storm (ENE St. Georges,  Bermuda)
 72H  27/1200Z...MERGED WITH FRONT AND LARGER LOW

NWS National Hurricane Center Miami FL 1100 AM AST Sun Sep 23 2018

The development of a subtropical storm that NHC and the global models have been advertising for the past several days has materialized, and based on satellite intensity classification from TAFB and earlier ASCAT data, advisories on Subtropical Storm Leslie have been initiated.

Leslie is still embedded within an upper-level low and strong winds are removed from the center. However, there is a chance as usual that the subtropical cyclone could develop additional convection near the center, and the transition to a tropical system during the next day or so is not out of the question. Global models do indicate that a new low is going to form north of Leslie, and that the subtropical cyclone will become absorbed by the new larger low. This is the scenario depicted by NHC at this time.

Leslie is embedded within very light steering currents, and most likely the cyclone will be meandering today and tomorrow. After that time, with the development of the new low to the north, Leslie will likely move east until it becomes absorbed.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 33.0N  46.5W   35 KT  40 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 12H  24/0000Z 33.2N  47.2W   40 KT  45 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 24H  24/1200Z 33.0N  47.5W   40 KT  45 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 36H  25/0000Z 33.0N  46.5W   40 KT  45 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 48H  25/1200Z 33.0N  45.0W   40 KT  45 MPH - Tropical Storm (ESE St. Georges,  Bermuda)
 72H  26/1200Z...ABSORBED BY LARGER LOW

NWS National Hurricane Center Miami FL 500 PM AST Sat Sep 22 2018

Since the last advisory was issued, deep convection decreased in association with the depression to the point that it was not classifiable with the Dvorak technique at 18Z. However, there are a couple of patches of thunderstorms that have developed recently, and if they persist they could help the system hold on to tropical cyclone status a bit longer. The low-level center remains exposed with UW-CIMSS now analyzing nearly 45 kt of westerly shear over the cyclone. Gradual spin down is expected during the next 12 to 24 hours, and the cyclone should become a remnant low by Sunday. Global model fields show the surface circulation dissipating by 36 hours and that is indicated in the official forecast.

The low-level center has been moving erratically today, with a recent northward jog seen, but the long-term initial motion estimate is 305/03. The weakening cyclone should be steered west- northwestward by a weak low-level ridge through dissipation, and the NHC track forecast has been nudged northward toward the latest multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 13.6N  53.9W   25 KT  30 MPH - Tropical Depression (ESE Bridgetown,  Barbados)
 12H  23/0600Z 13.9N  54.8W   25 KT  30 MPH - Tropical Depression (ESE Bridgetown,  Barbados)
 24H  23/1800Z 14.4N  56.0W   20 KT  25 MPH - Tropical Depression (ESE Bridgetown,  Barbados)
 36H  24/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 22 2018

It appears that the depression’s best day is behind it, as the cloud pattern has become less organized this morning. The low-level center is becoming increasingly separated from the warming cloud tops in what remains of the deep convection, which is displaced to the east by nearly 40 kt of west-southwesterly shear as analyzed by UW-CIMSS. The initial intensity has been lowered to 25 kt, consistent with a T1.0 classification from TAFB. Given that the strong shear is expected to continue and the depression will be moving through a relatively dry environment, the cyclone should gradually spin down and become a remnant low by 24 hours and dissipate by 48 hours. However, I would not be surprised if either or both of these occurred sooner.

The center of the depression hasn’t moved much during the past few hours, but a long-term initial motion estimate is 280/03. The weakening cyclone should be steered westward to west-northwestward by a low-level ridge. The new NHC track forecast is north of the previous one but remains along the southern edge of the guidance envelope given doubts about how much latitude such a shallow system will gain prior to dissipation.

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 13.2N  53.8W   25 KT  30 MPH - Tropical Depression (ESE Bridgetown,  Barbados)
 12H  23/0000Z 13.6N  54.5W   25 KT  30 MPH - Tropical Depression (ESE Bridgetown,  Barbados)
 24H  23/1200Z 14.0N  55.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  24/0000Z 14.4N  56.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  24/1200Z...DISSIPATED

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