Tropical Storm Oscar

Hurricane Oscar 1100 Hours October 31 2018
Hurricane Oscar 1100 Hours October 31 2018

NWS National Hurricane Center Miami FL 500 PM AST Wed Oct 31 2018

Tropical Storm Oscar (see 18 videos below) Satellite imagery and scatterometer data indicate that Oscar has become a hurricane-force extratropical low, as the central convection has all but dissipated and frontal-band-type cloud features have become better defined. The scatterometer data show hurricane-force winds about 70 n mi south of the center, and that the overall wind field has expanded considerably since the previous overpass. The cyclone is expected to maintain an intensity of 60-65 kt for the next 48 h, then gradually weaken as the baroclinic energy wanes, with dissipation occurring between 96-120 h over the far northeastern Atlantic.

The initial motion is now 030/30 kt. Oscar is now well embedded in the mid-latitude westerlies, and for the next 3-4 days it should move generally northeastward with a gradual decrease in forward speed.

Much of the current forecast, especially the intensity and the size, is based on input from the NOAA Ocean Prediction Center.

This is the last advisory on Oscar from the National Hurricane Center.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 39.3N  49.6W   65 KT  75 MPH - Post Tropical (ESE Chatham, MA)
 12H  01/0600Z 42.6N  46.6W   65 KT  75 MPH - Post Tropical (ESE Glace Bay, Nova Scotia, Canada)
 24H  01/1800Z 46.8N  41.4W   65 KT  75 MPH - Post Tropical (ESE St. John's, Newfoundland, Canada)
 36H  02/0600Z 50.7N  35.1W   60 KT  70 MPH - Post Tropical (WSW Baltimore, Ireland)
 48H  02/1800Z 54.2N  28.4W   60 KT  70 MPH - Post Tropical (WSW Belmullet, Ireland)
 72H  03/1800Z 59.5N  15.0W   55 KT  65 MPH - Post Tropical (WSW Twatt, Scotland)
 96H  04/1800Z 67.0N   2.0W   45 KT  50 MPH - Post Tropical (WSW Bodø, Norway)
120H  05/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Wed Oct 31 2018

Oscar is quickly transforming into an extratropical low. Although there is still a little bit of deep convection just north of the center, a more prominent cloud shield extends northward from the western part of the circulation. In addition, GOES-16 derived products show Oscar’s center nearly embedded within a frontal zone and cold air advection occurring on the back side of the system. The maximum winds are a bit uncertain, but for now they are held at 65 kt based on the Dvorak Current Intensity number from TAFB and the latest microwave estimates, which range from 60-70 kt.

Oscar is expected to complete extratropical transition later today when it becomes fully attached to the frontal boundary. Baroclinic energy is likely to keep the cyclone’s intensity relatively steady for the next 48 hours or so, although it should be noted that the GFS shows some intensification later today as a sting jet develops to the west of the center. After 48 hours, the post-tropical cyclone is expected to gradually lose strength, and the NHC intensity forecast continues to most closely follow the GFS model, which is at the high end of the guidance envelope. Despite this weakening, Oscar’s wind field is expected to grow substantially, affecting a large portion of the north Atlantic Ocean over the next several days.

A northeastward acceleration continues with an initial motion of 035/25 kt. Further acceleration toward the north Atlantic is expected during the next 48 hours while Oscar becomes more fully embedded within the mid-latitude flow. The new NHC track forecast was shifted slightly northward and westward from the previous forecast to trend closer to the latest consensus aids, but otherwise the track forecast reasoning remains unchanged.

Large swells from Oscar are expected to continue to affect portions of the coast of Bermuda through 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  31/1500Z 36.6N  51.6W   65 KT  75 MPH - Category 1 (ENE St. Georges, Bermuda)
 12H  01/0000Z 40.2N  48.7W   65 KT  75 MPH - Post Tropical (ESE Shelburne, Nova Scotia, Canada)
 24H  01/1200Z 44.5N  44.3W   65 KT  75 MPH - Post Tropical (ESE St. John's, Newfoundland, Canada)
 36H  02/0000Z 48.4N  38.7W   60 KT  70 MPH - Post Tropical (ESE St. John's, Newfoundland, Canada)
 48H  02/1200Z 52.1N  32.4W   60 KT  70 MPH - Post Tropical (ESE Prins Christianssund, Greenland)
 72H  03/1200Z 57.8N  18.6W   55 KT  65 MPH - Post Tropical (ENE Baleloch, Scotland)
 96H  04/1200Z 64.0N   5.5W   45 KT  50 MPH - Post Tropical (ENE Höfn, Iceland)
120H  05/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Tue Oct 30 2018

Hurricane Oscar – While conventional satellite imagery continues to show an area of deep convection over the center of Oscar, recent microwave data suggest that the inner core has become fragmented and that the circulation is tilted from southwest to northeast. The overall cloud pattern has also expanded northward as Oscar begins to interact with a frontal zone that is approaching the system from the northwest. A blend of the latest Dvorak T- and Current Intensity (CI) numbers yields an initial wind speed of 70 kt for this advisory. Oscar will be moving over decreasing SSTs and into an area of higher vertical wind shear tonight and Wednesday which is likely to cause some additional weakening during that time. The hurricane should complete its extratropical transition in about 24 hours, and the dynamical models indicate that the post-tropical cyclone is likely to maintain 60-65 kt winds for at least another couple of days. Some weakening is expected by 96 hours before the system merges with another low pressure area over the far northeastern Atlantic.

Oscar has turned northeastward and continues to accelerate. An additional increase in forward speed is anticipated during the next day or two, as the cyclone becomes embedded within deep-layer southwesterly flow ahead of a mid-latitude trough. Late in the period, the post-tropical low is forecast to slow down over the northeastern Atlantic. The track guidance remains in good agreement, except for some forward speed differences late in the period. The NHC track forecast is once again close to the various consensus aids and very similar to the previous advisory.

Large swells from Oscar are expected to continue to affect portions of the coast of Bermuda through Wednesday. 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  31/0300Z 32.8N  55.2W   70 KT  80 MPH - Category 1 (ENE St. Georges, Bermuda)
 12H  31/1200Z 35.6N  52.6W   65 KT  75 MPH - Category 1 (ENE St. Georges, Bermuda)
 24H  01/0000Z 40.2N  48.9W   65 KT  75 MPH - Category 1 (ESE Shelburne, Nova Scotia, Canada)
 36H  01/1200Z 44.3N  44.4W   65 KT  75 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
 48H  02/0000Z 48.2N  38.7W   60 KT  70 MPH - Tropical Storm (ENE St. John's, Newfoundland, Canada)
 72H  03/0000Z 55.2N  24.3W   60 KT  70 MPH - Tropical Storm (ESE Prins Christianssund, Greenland)
 96H  04/0000Z 61.0N  12.0W   50 KT  60 MPH - Tropical Storm (WSW Vágur, Faroe Islands)
120H  05/0000Z...MERGED WITH LARGER EXTRATROPICAL LOW

NWS National Hurricane Center Miami FL 500 PM AST Tue Oct 30 2018

Hurricane Oscar – Recent microwave imagery indicates that Oscar continues to maintain a small inner-core, however, it is tilted somewhat southwest to northeast with height due to increasing southwesterly wind shear. Cloud tops have continued to warm over the past few hours, and objective and subjective intensity estimates have decreased since this morning. The initial intensity has been lowered to 75 kt, based primarily on a blend of Final-T and Current Intensity estimates from TAFB and SAB.

The hurricane is moving over 24 deg C waters and a cold front associated with a large mid-latitude trough is quickly approaching from the west. This combination should soon kick off the extratropical transition (ET) process, and the most recent runs of the GFS, ECMWF, and UKMET indicate that Oscar will become fully extratropical within 36 h, if not sooner. Very gradual weakening is still expected during the next day or so while ET occurs, however, all of the dynamical models forecast that Oscar will be at or very near hurricane-strength when it becomes post-tropical. The maximum winds of the cyclone will likely slowly decrease thereafter, but Oscar will likely have a very large wind field and gale-force winds are possible over a large portion of the far north Atlantic. By day 5, the post-tropical low is forecast to merge with another mid-latitude low pressure system over the far northeastern Atlantic.

As expected, the hurricane is accelerating north-northeastward, with an initial motion estimate of 025/17 kt. Further acceleration is likely over the next 36 hours, and the global models are in remarkably good agreement on the track of the cyclone through that time. A turn toward the northeast is expected thereafter, and while there are still speed differences between the various global model solutions, the NHC forecast remains near the fairly steady multi-model consensus at all forecast hours. Almost no change was made to the official track forecast, which is merely an update of the previous advisory.

Although Oscar is forecast to move farther from Bermuda overnight, large swells from the hurricane are expected to affect portions of the island’s coast through Wednesday. 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  30/2100Z 31.3N  56.6W   75 KT  85 MPH - Category 1 (ESE St. Georges, Bermuda)
 12H  31/0600Z 33.8N  54.5W   70 KT  80 MPH - Category 1 (ESE St. Georges, Bermuda)
 24H  31/1800Z 38.3N  50.9W   65 KT  75 MPH - Category 1 (ESE New York City, NY)
 36H  01/0600Z 43.0N  46.8W   65 KT  75 MPH - Category 1 (ESE Glace Bay, Nova Scotia, Canada)
 48H  01/1800Z 46.7N  42.0W   60 KT  70 MPH - Tropical Storm (ESE St. John's, Newfoundland, Canada)
 72H  02/1800Z 54.0N  28.5W   55 KT  65 MPH - Tropical Storm (WSW Belmullet, Ireland)
 96H  03/1800Z 59.0N  15.0W   50 KT  60 MPH - Tropical Storm (WNW Arnol, Scotland)
120H  04/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Tue Oct 30 2018

Hurricane Oscar – Cloud-top temperatures have warmed a bit overall, and the convective pattern is becoming more asymmetric as dry air is infiltrating the southern and eastern part of Oscar’s circulation. However, the hurricane is still producing plenty of inner-core convection and some lightning strikes. Dvorak Current Intensity numbers from TAFB and SAB still support maximum winds of 90-100 kt, but objective numbers are much lower (65-75 kt), so Oscar’s initial intensity is lowered slightly to 85 kt.

Increasing shear and stronger upper-level divergence will likely offset each other in the short term, causing Oscar to maintain its intensity or only slightly weaken during the next 24 hours. However, a cold front is quickly approaching Oscar from the northwest, and their interaction is expected to cause Oscar to complete extratropical transition and become fully embedded within the frontal zone in about 36 hours. Oscar’s winds should gradually diminish after it becomes extratropical, but the NHC official forecast remains above the various consensus aids from 36 hours and beyond and lies closest to the GFS and ECMWF global models, which should have a good handle on the cyclone’s structure during the post-tropical phase.

Oscar continues to accelerate and has turned north-northeastward, or 020/12 kt, while entering the flow between a large high over the eastern/central Atlantic and a mid-latitude trough now moving over the western Atlantic. Oscar is expected to become embedded within the trough by 36 hours (the completion of extratropical transition), with the entire system becoming a cut-off low north of the jet stream by days 4 and 5.

The track models are in fairly good agreement on Oscar’s future path, but there are speed differences by the end of the forecast period. Of particular note, the ECMWF is much faster than the other models, showing a more progressive pattern on day 5. The NHC track forecast lies close to the previous official forecast to maintain continuity, but it is still faster than the GFS, HWRF, and the TVCN multi-model consensus at day 5.

(see video below from Maine 2017 storm)

Large swells from Oscar will affect Bermuda through Wednesday. 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  30/1500Z 29.7N  57.7W   85 KT 100 MPH - Category 1 (ESE St. Georges, Bermuda)
 12H  31/0000Z 31.8N  56.1W   80 KT  90 MPH - Category 1 (ESE St. Georges, Bermuda)
 24H  31/1200Z 35.6N  52.6W   80 KT  90 MPH - Category 1 (ENE St. Georges, Bermuda)
 36H  01/0000Z 40.6N  48.7W   75 KT  85 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
 48H  01/1200Z 45.1N  44.4W   65 KT  75 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
 72H  02/1200Z 52.6N  31.8W   55 KT  65 MPH - Tropical Storm (WSW Limerick, Ireland)
 96H  03/1200Z 59.0N  18.0W   50 KT  60 MPH - Tropical Storm (WSW Garenin, Scotland)
120H  04/1200Z 63.5N   6.5W   45 KT  50 MPH - Tropical Storm (ENE Gjógv, Faroe Islands)

NWS National Hurricane Center Miami FL 500 AM AST Tue Oct 30 2018

Hurricane Oscar eye is less distinct on infrared satellite imagery than it was several hours ago. Conventional and microwave imagery suggest that the center is tilted a bit to the northeast with height, and there continues to be some erosion of convection over the southwestern quadrant of the hurricane. This is indicative of some southwesterly shear over the system, and Oscar does not appear likely to strengthen further. The current intensity is held at 90 kt based on a blend of Dvorak Current Intensity numbers from TAFB and SAB. Model guidance indicates that the shear will not increase further until tonight, so the intensity is held steady for the next 12 hours.

After that time, south-southwesterly shear if forecast to increase and become quite high in 36-48 hours. Around that time, global models show Oscar interacting with a frontal zone, and causing significant warm and cold air advection around the center, indicating the transition to a vigorous extratropical cyclone. Not surprisingly, the global guidance also shows a substantial increase in the size of the system during and after the extratropical transformation, and this is reflected in the NHC wind radii forecasts.

Oscar is beginning to move faster, just to the east of due north, or around 010/11 kt. There is little change to the track forecast reasoning from the previous advisory. Over the next couple of days, Oscar should continue to accelerate, toward the north-northeast, in the flow on the southeast side of a mid-latitude trough that has just moved off the United States east coast. Later in the period, post-tropical Oscar should become more embedded within the trough and in the mid-latitude westerlies, and move northeastward over the northeastern Atlantic. The official track forecast is similar to the previous one and is a blend of the simple and corrected dynamical model consensus predictions.

Large swells from Oscar will affect Bermuda through Wednesday. 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  30/0900Z 28.6N  58.2W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 12H  30/1800Z 30.6N  57.1W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 24H  31/0600Z 34.0N  54.3W   85 KT 100 MPH - Category 1 (ESE St. Georges, Bermuda)
 36H  31/1800Z 38.5N  50.5W   80 KT  90 MPH - Category 1 (ESE NYC, New York)
 48H  01/0600Z 43.5N  46.7W   65 KT  75 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
 72H  02/0600Z 50.5N  35.5W   55 KT  65 MPH - Tropical Storm (ESE St. Anthony, Newfoundland, Canada)
 96H  03/0600Z 57.5N  21.5W   50 KT  60 MPH - Tropical Storm (WSW Castlebay, Scotland)
120H  04/0600Z 63.0N   9.0W   45 KT  50 MPH - Tropical Storm (WNW Gjógv, Faroe Islands)

NWS National Hurricane Center Miami FL 1100 PM AST Mon Oct 29 2018

Hurricane Oscar  – The satellite presentation of Oscar continued to improved after the release of the previous advisory, with the small eye becoming a little more distinct around 0000 UTC, but it has again become cloud filled within the past hour or so. Recent microwave imagery continues to depict a tiny eye with a solid ring of deep convection surrounding it, but there is little outer banding over the southwestern portion of the circulation likely due to shear and dry air. Objective satellite intensity estimates which may be having trouble discerning the small eye are around 80 kt, while subjective T-numbers range from T5.0 from SAB to T5.5 from TAFB. As a result, the initial intensity has been increased to 90 kt for this advisory.

Although the NHC intensity forecast does not explicitly show additional strengthening, Oscar has another 12 hours or so over SSTs of 26-26.5 deg C in which some slight intensification could occur. After that time, increasing southwesterly shear and cooler waters along the forecast track should cause the hurricane to weaken gradually as extratropical transition begins. Oscar is forecast to complete extratropical transition in about 48 hours, and remain a powerful post-tropical cyclone over the north Atlantic for much of the forecast period. The global models indicate that Oscar’s wind field will quickly expand during its transition to a post-tropical cyclone, and this is reflected in the NHC wind radii forecast.

The hurricane has been moving slightly east of due north or 010/8 kt. Oscar is forecast to begin to accelerate north-northeastward or northeastward ahead of a deep-layer trough that will be moving over the western Atlantic on Tuesday. The hurricane should be well embedded within the deep-layer southwesterly flow ahead of the trough by Tuesday night or Wednesday, and the cyclone is expected to move rapidly northeastward across the north-central and northeastern Atlantic later this week. There has been little change to the guidance envelope, and the new NHC track forecast is essentially an update of the previous advisory. The official forecast again lies near the various consensus aids and is near the middle of the tightly clustered model guidance.

Although Oscar is not expected to directly affect any land areas, large swells from Oscar will affect Bermuda through Wednesday. 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  30/0300Z 27.4N  58.3W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 12H  30/1200Z 28.8N  57.7W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 24H  31/0000Z 31.5N  55.6W   85 KT 100 MPH - Category 1 (ESE St. Georges, Bermuda)
 36H  31/1200Z 35.3N  52.1W   80 KT  90 MPH - Category 1 (ESE St. Georges, Bermuda)
 48H  01/0000Z 40.1N  47.8W   70 KT  80 MPH - Category 1 (ESE Shelburne, Nova Scotia, Canada)
 72H  02/0000Z 49.1N  36.4W   60 KT  70 MPH - Tropical Storm (ENE Joe Batt's Arm, Newfoundland, Canada)
 96H  03/0000Z 56.2N  22.0W   55 KT  65 MPH - Tropical Storm (ESE Portnahaven, Scotland)
120H  04/0000Z 62.5N   9.5W   45 KT  50 MPH - Tropical Storm (WNW Gjógv, Faroe Islands)

NWS National Hurricane Center Miami FL 500 PM AST Mon Oct 29 2018

Hurricane Oscar –  The overall cloud pattern of Oscar is somewhat asymmetrical, and convective banding is limited to the eastern semicircle of the cyclone. However, recent visible and microwave imagery indicate that tight eyewall of the hurricane is still very well defined, despite the 20 kt or more of westerly shear analyzed in SHIPS and UW-CIMSS diagnostics. It appears that the shear is not having much of an affect on Oscar’s inner-core, and in fact the small eye of the hurricane has become better defined over the past 6 hours. Recent objective and subjective intensity estimates support an intensity of 75-80 kt, and given the small radius of maximum winds (RMW) of Oscar, it seems more appropriate to round up, yielding an estimated intensity of 80 kt.

All of the dynamical intensity guidance calls for additional intensification in the short term. Persistent lightning inside the hurricane’s RMW during the past several hours also supports the notion of additional strengthening, as this signal has been associated with intensifying hurricanes in the past. By 24 h and beyond, Oscar will likely level off in intensity and then begin to weaken while it moves over much cooler SSTs and begins extratropical transition. Although this process will likely result in a rapid expansion of Oscar’s tropical-storm-force wind field, it should also cause the maximum winds associated with the cyclone to steadily decrease through the end of the week. The NHC intensity forecast is similar to the previous advisory, and generally follows IVCN through the forecast period.

Oscar’s eye has wobbled during the past several hours, but the hurricane appears to have already begun its expected turn toward the north. The hurricane is essentially on-track, and no major changes were required to the NHC track forecast. A large mid-latitude trough to the west will likely cause Oscar to accelerate north-northeastward or northeastward beginning by late Tuesday, and then rapidly move across the northern central Atlantic in that direction. The global models are in reasonably good agreement on the speed and heading of Oscar through day 5, which is somewhat unusual for a recurving cyclone. The new official track forecast is based on a blend of the simple and corrected multi-model consensus aids, and confidence in the track forecast is fairly high.

Although Oscar is not expected to directly affect any land areas, large swells from Oscar will affect Bermuda through Wednesday. 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  29/2100Z 26.5N  58.5W   80 KT  90 MPH - Category 1 (ESE St. Georges, Bermuda)
 12H  30/0600Z 27.8N  58.4W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 24H  30/1800Z 29.9N  57.2W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 36H  31/0600Z 33.0N  54.3W   85 KT 100 MPH - Category 1 (ESE St. Georges, Bermuda)
 48H  31/1800Z 37.3N  50.3W   80 KT  90 MPH - Category 1 (ESE St. Georges, Bermuda)
 72H  01/1800Z 46.7N  40.0W   60 KT  70 MPH - Tropical Storm (ESE St. John's, Newfoundland, Canada)
 96H  02/1800Z 54.0N  25.0W   55 KT  65 MPH - Tropical Storm (ESE Dooagh, Ireland)
120H  03/1800Z 60.0N  12.0W   50 KT  60 MPH - Tropical Storm (ESE Sunnbøur, Faroe Islands)

NWS National Hurricane Center Miami FL 200 PM EDT Mon Oct 29 2018

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

The National Hurricane Center is issuing advisories on Hurricane Oscar, located over the central Atlantic Ocean.

NWS National Hurricane Center Miami FL 1100 AM AST Mon Oct 29 2018

Hurricane Oscar convective cloud pattern has continued to improve since the previous advisory, with a small, cloud-filled eye now apparent in visible satellite imagery and also in a recent SSMI/S microwave pass. In addition, cirrus outflow has been expanding in all quadrants, especially in the eastern semicircle. The initial intensity of 75 kt is based on a Dvorak satellite intensity estimate of T4.5/77 kt from TAFB, a Data-T-number of T4.5/77 kt from SAB, and an NHC objective intensity estimate of T4.4/75 kt. It is also worth noting that bursts of lightning activity in the eastern eyewall have been occurring since around 1100 UTC.

The initial motion estimate is now 285/06 kt. Oscar has slowed its forward motion significantly and has made the advertised turn toward the west-northwest. A motion toward the northwest is expected by late afternoon today as the hurricane rounds the southwestern periphery of a deep-layer ridge. A turns toward the north and then toward the north-northeast are forecast on Tuesday as Oscar moves north of the ridge axis ahead of an eastward-moving deep-layer trough currently approaching Bermuda. The trough is expected to continue advancing eastward over the next couple of days, accelerating Oscar toward the northeast at forward speeds near 25 kt on Wednesday through Friday.

Although a strong shortwave trough is still forecast to dig southward to the west of Oscar on Wednesday, none of the model guidance shows the hurricane being captured any longer, and instead keep the cyclone as a separate entity that accelerates northeastward into the mid-latitude westerlies as a strong extratropical cyclone. The official track forecast is similar to the previous advisory, and lies close to an average of the corrected-consensus models HCCA and FSSE and the simple consensus models TVCA and TVCX.

Deep-layer (850-200 mb) shear calculations by the SHIPS model and UW-CIMSS are at least 25 kt from the northwest, which clearly is not negatively affecting the improving cirrus outflow. This is likely due to the large 1000-km domain that the SHIPS model uses to compute vertical wind shear. Furthermore, most of the cloud top temperatures within the outflow layer appear to be mostly below the 200-mb level, and closer to the 250-mb level. The large shear values are resulting in much less intensification forecast by the SHIPS and LGEM statistical-dynamical intensity models. As a result, the official intensity forecast leans more toward the HCCA and FSSE models, which are weighing more heavily the stronger intensity forecasts provided by the HWRF, HMON, and Navy COAMPS-TC models, which have Oscar strengthening to just below major hurricane status in 24-36 hours. By 48 hours and beyond, sharply decreasing SSTs along with increasing southwesterly shear ahead of a deep-layer trough are expected to cause Oscar to gradually weaken and transition to a strong extratropical low in 60-72 hours.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 25.8N  58.4W   75 KT  85 MPH - Category 1 (ESE St. Georges, Bermuda)
 12H  30/0000Z 26.8N  58.7W   85 KT 100 MPH - Category 1 (ESE St. Georges, Bermuda)
 24H  30/1200Z 28.7N  58.0W   90 KT 105 MPH - Category 2 (ESE St. Georges, Bermuda)
 36H  31/0000Z 31.4N  56.1W   90 KT 105 MPH - Category 2 (ENE St. Georges, Bermuda)
 48H  31/1200Z 35.0N  52.6W   80 KT  90 MPH - Category 1 (ENE St. Georges, Bermuda)
 72H  01/1200Z 43.0N  43.7W   65 KT  75 MPH - Category 1 (ESE Lockeport. Nova Scotia, Canada)
 96H  02/1200Z 50.0N  30.0W   60 KT  70 MPH - Tropical Storm (ESE St. John's, Newfoundland, Canada)
120H  03/1200Z 55.0N  15.0W   55 KT  65 MPH - Tropical Storm (ESE Donegal, Ireland)

NWS National Hurricane Center Miami FL 500 AM AST Mon Oct 29 2018

Hurricane Oscar – The cloud pattern of Oscar has continued to become better organized, with a growing CDO and convective banding features are better defined, especially over the southern semicircle of the hurricane. Upper-level outflow is gradually becoming better established to the south. Although the most recent Dvorak Current Intensity estimates from TAFB and SAB are at 65 kt, given that the eye is becoming better defined, the advisory intensity is set at 70 kt. Oscar is currently under some northerly to north-northwesterly shear, but the shear is expected to diminish somewhat later today.

Also, the tropical cyclone is expected to move through a modestly moist air mass for the next day or two. Therefore, additional strengthening is forecast through 36 hours in agreement with the latest intensity model consensus. Around 48 hours into the forecast period, the shear begins to increase significantly, with notably cooler SSTs. This should lead to the onset of a steady weakening trend. By about 72 hours, the global models indicate that Oscar will become embedded in a frontal zone, so the official forecast shows the system becoming an extratropical cyclone at that time.

Oscar has slowed its forward motion and is now moving at about 270/11 kt. A mid-level high to the north of the cyclone is expected to quickly shift eastward, while a mid-latitude trough approaches Oscar from the west in a day or so. This evolution of the steering flow should cause Oscar to turn northward to north-northeastward in 24-48 hours. Later in the forecast period, Oscar is likely to move quickly northeastward on the eastern side of the trough. There has been some inconsistencies in the track model guidance around 5 days over the last few forecast cycles, with the model consensus, TVCN, shifting significantly southward and then northward. The official forecast track is somewhat to the left of the previous one near the end of the period, to reflect the latest consensus prediction.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 25.7N  57.8W   70 KT  80 MPH - Category 1 (ESE St. Georges, Bermuda)
 12H  29/1800Z 26.1N  58.7W   75 KT  85 MPH - Category 1 (ESE St. Georges, Bermuda)
 24H  30/0600Z 27.7N  58.7W   80 KT  90 MPH - Category 1 (ESE St. Georges, Bermuda)
 36H  30/1800Z 30.0N  57.5W   85 KT 100 MPH - Category 2 (ESE St. Georges, Bermuda)
 48H  31/0600Z 33.0N  54.7W   85 KT 100 MPH - Category 2 (ENE St. Georges, Bermuda)
 72H  01/0600Z 41.5N  46.5W   70 KT  80 MPH - Category 1 (ESE Lockeport. Nova Scotia, Canada)
 96H  02/0600Z 46.0N  35.5W   60 KT  70 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
120H  03/0600Z 48.0N  26.0W   55 KT  65 MPH - Tropical Storm (WSW Brest, France)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Oct 28 2018

Tropical Storm Oscar – Deep convection has redeveloped near the center of Oscar since early this morning and its low-level center is no longer exposed. Satellite intensity estimates have not changed since last night and the estimated intensity of 60 kt is above the various techniques. The initial intensity estimate is based primarily on the latest available ASCAT data from last night around 0100 UTC that showed maximum winds of 55-60 kt. Given the recent increase in convection observed near the center of Oscar, it seems unlikely that the winds have decreased since that time. It is worth noting that the small inner-core of Oscar increases the uncertainty of the intensity estimate, and could make the cyclone susceptible to short term intensity fluctuations that are nearly impossible to forecast or precisely detect.

Virtually no change has been made to the intensity forecast. The tropical storm is moving over sufficiently warm water to support intensification and it is located within a light to moderate shear environment. All the intensity models forecast at least some strengthening, and Oscar is expected to become a hurricane later today or tonight, with some additional strengthening possible through Wednesday. Extratropical transition is forecast to begin soon thereafter, which will likely result in a decrease in the maximum winds, even as the extent of tropical-storm-force winds rapidly increases. This process is expected to be complete by 120 h. The new NHC intensity forecast is very close to the intensity consensus IVCN at all forecast hours.

Oscar turned abruptly westward earlier this morning, and the initial motion estimate is now 270/10 kt. The tropical cyclone is forecast to continue moving generally westward for another 12 to 24 h on the south side of a mid-layer ridge over the northern central Atlantic. Oscar should then turn toward the north between the ridge and a mid-latitude trough approaching from the west. By Wednesday, the cyclone is expected to accelerate north-northeastward or northeastward as it becomes embedded in deep-layer southwesterly flow ahead of the aforementioned trough. All of the global models agree on this general scenario, though there are differences regarding the exact timing that Oscar will begin its recurvature and how quickly it will accelerate across the northern Atlantic. That said, the track consensus aids have changed very little, and no significant changes were made to the previous track forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 25.5N  53.8W   60 KT  70 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 12H  29/0000Z 25.6N  55.8W   65 KT  75 MPH - Category 1 (ESE St. Georges, Bermuda)
 24H  29/1200Z 26.2N  57.8W   65 KT  75 MPH - Category 1 (ESE St. Georges, Bermuda)
 36H  30/0000Z 27.3N  58.4W   70 KT  80 MPH - Category 1 (ESE St. Georges, Bermuda)
 48H  30/1200Z 29.3N  57.8W   75 KT  85 MPH - Category 1 (ESE St. Georges, Bermuda)
 72H  31/1200Z 37.1N  51.3W   80 KT  90 MPH - Category 1 (ENE St. Georges, Bermuda)
 96H  01/1200Z 45.5N  40.0W   65 KT  75 MPH - Category 1 (ESE St. John's, Newfoundland, Canada)
120H  02/1200Z 53.0N  22.0W   55 KT  65 MPH - Post Tropical (WSW Doolin, Ireland)

NWS National Hurricane Center Miami FL 1100 PM AST Sat Oct 27 2018

-Satellite imagery shows that convection associated with Oscar has become better organized, with increased banding around the low- level center. In addition, recent scatterometer data indicate that the system now has a relatively small wind field with a radius of maximum winds of about 25 n mi. Although the cyclone is still tangled up with the upper-level low to the point where it has not yet developed the anticyclonic outflow of a tropical cyclone, the convection and the wind field now justify calling the system a tropical storm. The initial intensity has been raised to 55 kt based on the scatterometer data, and it is possible this is a little conservative.

The initial motion is a somewhat uncertain 240/17, as the short-term motion has been more toward the southwest or south. For the next several hours, Oscar should continue to pivot around the upper-level low to its east. Thereafter, it should turn more westward with a decrease in forward speed on the south side of a large ridge over the North Atlantic. After about 36 h, a large deep-layer trough moving eastward across the western Atlantic should cause Oscar to turn northwestward and northward, followed by recurvature into the westerlies and acceleration. The track guidance is generally in good agreement with this scenario, although by 120 h there is some spread in both the direction and forward speed after recurvature. The new forecast track is near the various consensus models, and the early part of it is shifted a little to the south of the previous forecast due to the current location and motion.

The global models suggest that the core of Oscar should mostly avoid nearby strong upper-level winds through 24-36 h, and then encounter strong upper-level divergence associated with the deep-layer trough. While the environment is not ideal for a tropical cyclone, conditions appear favorable for additional intensification, and the intensity forecast now calls for Oscar to reach hurricane strength in about 24 h. Interaction with the trough after 72 h should start extratropical transition, which should be complete between 96-120 h.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0300Z 25.7N  51.4W   55 KT  65 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 12H  28/1200Z 25.2N  54.1W   60 KT  70 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 24H  29/0000Z 25.1N  56.5W   65 KT  75 MPH - Category 1 (ESE St. Georges, Bermuda)
 36H  29/1200Z 25.8N  58.2W   70 KT  80 MPH - Category 1 (ESE St. Georges, Bermuda)
 48H  30/0000Z 27.2N  58.6W   75 KT  85 MPH - Category 1 (ESE St. Georges, Bermuda)
 72H  31/0000Z 32.5N  55.5W   75 KT  85 MPH - Category 1 (ENE St. Georges, Bermuda)
 96H  01/0000Z 41.0N  47.0W   70 KT  80 MPH - Category 1 (ENE NYC, New York)
120H  02/0000Z 48.5N  32.0W   60 KT  70 MPH - Tropical Storm (ENE St. Georges, Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Sat Oct 27 2018

Oscar is still located beneath an upper-level low, however it its convective structure is now more reminiscent of a tropical cyclone. Deep convection is primarily occuring in a small burst just south of the center of Oscar, however this convective activity appears to be displaced by light northerly shear associated with the upper-low. Earlier AMSU sounding data indicated that the cyclone has developed a weak but vertically deep warm core which also indicates that Oscar is nearly a tropical cyclone, if it isn’t one already. Oscar is moving quickly westward away from the upper-low, and will likely become a tropical storm later tonight if its current structural trends continue.

The initial intensity is held at 50 kt, based primarily on the latest Hebert-Poteat subtropical intensity estimate from TAFB. The intensity guidance has bounced back, and the most of the intensity guidance is higher than it was six hours ago. While little change was made to the NHC intensity forecast, it now lies very near the intensity consensus at all forecast hours. Gradual intensification is still expected and Oscar is forecast to approach hurricane strength by Monday. Slight additional intensification is possible through the middle of next week, until extratropical transition occurs by 120 h.Subtropical Storm Oscar Wind Probilities 1400 Hours October 27 2018

Oscar moved very quickly westward this afternoon, but a more representative motion estimate is 265/15 kt. The latest runs of the typically reliable global models are in better agreement than they were this morning. Oscar is forecast to move west-southwestward or westward for the next day or two on the south side of a mid-level ridge to the north. The cyclone is then expected to recurve and accelerate northeastward ahead of a substantial mid-latitude trough moving across the western and central Atlantic by the middle of next week. The official track forecast has been adjusted westward to bring it closer to the latest track consensus, especially for the first 72 h of the forecast. By day 5, the official forecast is quite similar to the previous advisory, but with a slightly slower forward speed for Oscar.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 26.9N  50.7W   50 KT  60 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 12H  28/0600Z 26.1N  53.0W   50 KT  60 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 24H  28/1800Z 25.7N  55.8W   55 KT  65 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 36H  29/0600Z 25.6N  57.9W   55 KT  65 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 48H  29/1800Z 26.4N  59.1W   60 KT  70 MPH - Tropical Storm (ESE St. Georges, Bermuda)
 72H  30/1800Z 30.6N  57.5W   70 KT  80 MPH - Category 1 (ESE St. Georges, Bermuda)
 96H  31/1800Z 38.5N  50.0W   70 KT  80 MPH - Category 1 (ESE NYC, New York)
120H  01/1800Z 46.5N  38.0W   60 KT  70 MPH - Post Tropical (WSW St. John's, Newfoundland, Canada)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Oct 27 2018

Oscar’s organization has improved this morning. Although the subtropical storm is still entangled with an upper-level low, convection has increased near the center of the cyclone since last night. The most recent Hebert-Poteat subtropical intensity estimate from TAFB has increased accordingly to 45-50 kt. Furthermore, Canadian drifting buoy 47546 recently reported a minimum pressure of just below 996 mb to the east of Oscar’s center, suggesting the central pressure of the cyclone has decreased since the last advisory. The initial intensity is therefore increased to 50 kt for this advisory.

Little change has been made to the intensity forecast. The GFS and many of its associated models (HWRF, DSHP, LGEM) have changed abruptly and forecast far less intensification than they did just 6 hours ago. However, the CTCI, HMON, and ECMWF-based statistical guidance still show Oscar reaching hurricane strength within a few days. Rather than chase a possible short-term trend in the intensity guidance, the official intensity forecast will stay the course for now and is a little above the intensity consensus, bringing Oscar to hurricane strength in around 48 h. After that time, some slight additional intensification is possible, but Oscar is ultimately expected to undergo extratropical transition by the end of the forecast period, which should cause the cyclone to steadily weaken.

Oscar has turned toward the west and the initial motion estimate is now 270/11 kt. A west-southwestward motion is anticipated later today as Oscar moves around the back side of an mid- to upper-level trough over the central Atlantic, followed by a turn toward the west on the south side of a subtropical ridge to the north. As long as Oscar intensifies as forecast, it should turn sharply northeastward early next week ahead of a mid-latitude trough advancing across the western and central Atlantic, and then accelerate in that direction while undergoing extratropical transition. The GFS is an outlier, showing a much weaker and vertically shallow cyclone that does not fully recurve, but all of the other global models are in generally good agreement with the scenario listed above. Despite the inconsistency of the GFS, the model consensus has not changed significantly since the last advisory, so only minor adjustments were made to the NHC track forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 27.3N  48.4W   50 KT  60 MPH - Tropical Storm (WSW St. Georges, Bermuda)
 12H  28/0000Z 26.9N  50.6W   55 KT  65 MPH - Tropical Storm (WSW St. Georges, Bermuda)
 24H  28/1200Z 26.2N  53.5W   60 KT  70 MPH - Tropical Storm (WSW St. Georges, Bermuda)
 36H  29/0000Z 25.9N  56.1W   60 KT  70 MPH - Tropical Storm (WSW St. Georges, Bermuda)
 48H  29/1200Z 26.5N  57.4W   65 KT  75 MPH - Category 1 (WSW St. Georges, Bermuda)
 72H  30/1200Z 30.2N  57.0W   70 KT  80 MPH - Category 1 (WSW St. Georges, Bermuda)
 96H  31/1200Z 37.0N  50.0W   70 KT  80 MPH - Category 1 (WNW St. Georges, Bermuda)
120H  01/1200Z 47.0N  38.0W   60 KT  70 MPH - Post Tropical (WSW St. John's, Newfoundland, Canada)

NWS National Hurricane Center Miami FL 800 AM EDT Fri Oct 26 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: 1.

A low pressure system located about 1200 miles east-northeast of the northern Leeward Islands has changed little in organization since last night.

However, environmental conditions appear conducive for further development and this system will likely become a tropical or subtropical cyclone later today or tonight while it moves generally northward over the central Atlantic. After that time, the low is forecast to turn westward and remain well to the north or northeast of the Lesser Antilles through early next week.

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

NWS National Hurricane Center Miami FL 800 PM EDT Thu Oct 25 2018

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

Shower activity associated with a low pressure system centered about 1000 miles east-northeast of the northern Leeward Islands has become more concentrated during the past several hours.

The low is expected to move generally northward over the next couple of days into an area where environmental conditions are forecast to be conducive for further development, and a tropical or subtropical storm is expected to form by early this weekend. After that time, the system is forecast to turn westward well to the north or northeast of the Lesser Antilles through early next week.

* 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 Oct 25 2018

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

A low pressure system centered nearly 1000 miles east-northeast of the northern Leeward Islands has changed little in organization since this morning.

However, the low is expected to move generally northward over the next couple of days into an area where environmental conditions are forecast to be conducive for further development, and a tropical or subtropical storm is likely to form by early this weekend. After that time, the system is forecast to turn westward well to the north or northeast of the Lesser Antilles through early next week.

* Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Thu Oct 25 2018

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

A low pressure system centered about 900 miles east-northeast of the northern Leeward Islands is gradually becoming better defined and the associated shower and thunderstorm activity is showing signs of organization.

This low is expected to move generally northward over the next couple of days into an area where environmental conditions are forecast to be conducive for further development, and a tropical or subtropical storm is likely to form by early this weekend. After that time, the system is forecast to turn westward well to the north or northeast of the Lesser Antilles through early next week.

* Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high...80 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Wed Oct 24 2018

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

A large area of disturbed weather over the central tropical Atlantic Ocean is associated with a broad area of low pressure located about 900 miles east of the northern Leeward Islands. This system has become better organized since yesterday with increased thunderstorm activity, although the low’s circulation is still not well defined.

This disturbance is expected to move northward over the next couple of days into an area where environmental conditions are forecast to be generally conducive for development, and a tropical or subtropical depression or storm is most likely to form on Friday or Saturday. After that time, the system is forecast to turn westward well to the northeast of the Lesser Antilles through early next week.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...70 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Wed Oct 24 2018

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

A large area of disorganized showers and thunderstorms over the central tropical Atlantic Ocean is associated with a broad area of low pressure located about 900 miles east of the northern Leeward Islands. This system is expected to move slowly northward over the next few days into an area where environmental conditions are forecast to be more conducive for development.

A tropical or subtropical depression could form over the weekend while the system turns westward well to the northeast of the Lesser Antilles.

* Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Wed Oct 24 2018

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

 A large area of disorganized showers and thunderstorms over the central tropical Atlantic Ocean is associated with a broad area of low pressure located a little over 900 miles east of the northern Leeward Islands. This system is expected to move slowly northward over the next few days into an area where environmental conditions are forecast to be more conducive for development. A tropical or subtropical depression could form over the weekend while the system turns westward well to the northeast of the Lesser Antilles.

* Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium...60 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Tue Oct 23 2018

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

1. A large area of cloudiness and showers over the central tropical Atlantic Ocean is associated with a surface trough. This trough is expected to move slowly northward over the next few days into an area where environmental conditions are forecast to be more conducive for development. A tropical or subtropical depression could form over the weekend while the system turns westward well to the northeast of the Lesser Antilles.

* Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Tue Oct 23 2018

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

Tropical Storm Oscar Forming? –  A broad area of low pressure is expected to form in a couple of days several hundred miles east-northeast of the northern Leeward Islands.

Some tropical or subtropical development of this system is possible by the weekend while it meanders over the central Atlantic Ocean.

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