Tropical Storm Larry

Post Tropical Storm Larry Track 1100 Hours September 11 2021
Post Tropical Storm Larry Track 1100 Hours September 11 2021

Hurricane Larry Wind Speed FieldHurricane LarryNWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 11, 2021 (see video below)

Satellite images indicate that Larry has completed its transition to a post-tropical cyclone with most of the deep convection dissipating near the low-level center and frontal features developing. In addition, the low- and mid-level centers are now well separated, and the cyclone appears a little weaker. The initial intensity is estimated to be 60 kt. The post-tropical system is very large and gale-force winds and high seas extend far from the center. It is interesting to note that up to just several hours ago Larry had maintained an inner core and a fairly tropical appearance despite being at very high latitudes and over quite cold water. Larry is racing northeastward, with the initial motion estimated to be 030/42 kt. The storm is expected to merge with another large extratropical low tonight or early Sunday.

This is the last NHC advisory on Larry.

Key Messages:

  • 1. Large swells generated by Post-Tropical Cyclone Larry will continue to affect portions of the the east coast of the United States and Atlantic Canada through tonight. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials.
FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 54.0N  48.2W   60 KT  70 MPH - Post Tropical (ENE St. Anthony,NF Canada)
 12H  12/0000Z 57.8N  44.9W   55 KT  65 MPH - Post Tropical (ESE Nanortalik,Greenland)
 24H  12/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Fri Sep 10, 2021 

Larry remains a well organized hurricane at a high latitude, and it is quickly approaching southeastern Newfoundland. Satellite images show a fairly tight inner core and large curved bands surrounding that feature. However, there are some notable dry slots between the core and bands that have developed during the past several hours. The latest Dvorak numbers have nudged downward, with the CI values ranging between 65 kt and 72 kt. Based on these estimates, and a very recent ASCAT pass that showed peak winds near 65 kt, the initial intensity is set at 70 kt for this advisory. The cyclone remains quite large, with hurricane-force winds and tropical-storm-force winds estimated to extend outward up to 80 and 210 n mi from the center, respectively.

The hurricane is in the process of turning to the right, with the latest initial motion estimated to be a fairly quick 015/25 kt. An even faster north-northeast to northeast motion is expected during the next day or two as the hurricane moves in the fast flow between a mid- to upper-level trough over the northeastern U.S./eastern Canada and a mid-level ridge over the central Atlantic. This motion should take Larry across southeastern Newfoundland tonight. Larry is then expected to merge with a large extratropical low over the Labrador Sea on Sunday. The NHC track forecast is similar to the previous one and near the middle of the guidance envelope.

Although Larry will be moving over cooler waters north of the Gulf Stream Current later today, the hurricane will likely hold its strength or weaken just a little before landfall. After landfall, the models show the inner core dissipating, and the combination of land interaction, cooler waters, and an increase in shear should cause weakening and lead to extratropical transition by early Saturday. The NHC intensity forecast is close to the GFS model, which often performs well for hurricanes that transition to extratropical cyclones.

Key Messages:

  • 1. Larry is forecast to move over portions of southeastern Newfoundland tonight as it undergoes transition to a hurricane-force post-tropical cyclone. Hurricane conditions, a dangerous storm surge, and heavy rainfall are expected in portions of southeastern Newfoundland where a Hurricane Warning in effect.
  • 2. Large swells generated by Larry will continue to affect the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through Saturday night. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials.
FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 40.0N  60.5W   70 KT  80 MPH - Category 1 (ESE New York,NY)
 12H  11/0000Z 45.1N  56.4W   70 KT  80 MPH - Category 1 (ESE Sydney,NS Canada)
 24H  11/1200Z 52.0N  49.4W   60 KT  70 MPH - Post Tropical (ENE St. Anthony,NF Canada)
 36H  12/0000Z 57.5N  44.0W   60 KT  70 MPH - Post Tropical (ESE Nanortalik,Greenland)
 48H  12/1200Z 61.1N  38.7W   55 KT  65 MPH - Post Tropical (ENE Nanortalik,Greenland)
 60H  13/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Thu Sep 09, 2021

There is not much new to report in the satellite structure with Larry this evening. The hurricane consists of a small core region of cold convective cloud tops near and just north of the center with a much larger concentric band of more moderate convective activity encircling the smaller core. Radar from Bermuda also shows this structure well even as the hurricane pulls away from the island. The most recent subjective Dvorak satellite intensity estimates from SAB and TAFB were unchanged from this afternoon, and the initial intensity will remain at 80 kt for this advisory.

Larry is now moving to the north and beginning to accelerate at 360/20 kt. The track guidance remains in good agreement that Larry should soon turn to the northeast and continue accelerating quickly ahead of a large mid-latitude trough. On the current track, Larry should pass near or over southeastern Newfoundland tomorrow night or Saturday morning, becoming post-tropical shortly after it passes by. The post-tropical cyclone Larry should continue to move rapidly to the northeast until it is absorbed by the aforementioned mid-latitude trough after 48 hours. The official track forecast again lies close to the various consensus model predictions, and is just a touch faster than the previous forecast.

Larry has another 12 hours or so over warm Gulf Stream waters, and most of the guidance is in agreement that the hurricane should maintain its intensity in the short-term. However, more gradual weakening should begin thereafter once Larry moves over much cooler waters. Unfortunately, there is not much time for Larry to weaken before the hurricane impacts Newfoundland, and it also is possible the rapidly approaching mid-latitude trough will provide some baroclinic forcing that could expand the wind field of the hurricane further. The NHC intensity forecast remain close to the latest HCCA guidance which is quite similar to the previous forecast. After 24 hours, the latest forecast GFS and ECMWF simulated IR brightness temperature suggest that Larry’s convection should quickly shear off after passing by Newfoundland, with the hurricane becoming a powerful post-tropical cyclone by 36 hours. Both of these models now also suggest the post-tropical cyclone will quickly be stretched and then absorbed as its captured by an even larger extratropical cyclone produced by the upstream trough after 48 hours.

Key Messages:

  • 1. Larry is forecast to move near or over portions of southeastern Newfoundland Friday night or early Saturday morning as it undergoes transition to a hurricane-force post-tropical cyclone. Hurricane conditions and dangerous storm surge are expected in portions of southeastern Newfoundland where a Hurricane Warning in effect.
  • 2. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through the end of the week. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials.
FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z 35.5N  62.3W   80 KT  90 MPH - Category 1 (ESE St. George's,Bermuda)
 12H  10/1200Z 39.0N  60.9W   80 KT  90 MPH - Category 1 (ENE St. George's,Bermuda)
 24H  11/0000Z 45.1N  56.1W   75 KT  85 MPH - Category 1 (ESE Sydney,NS Canada)
 36H  11/1200Z 52.0N  49.3W   65 KT  75 MPH - Category 1 (ENE St Johns,NF Canada)
 48H  12/0000Z 58.1N  44.0W   60 KT  70 MPH - Tropical Storm (ESE Nanortalik,Greenland)
 60H  12/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Thu Sep 09, 2021 

Larry continues to feature a banding-type eye on satellite images, and the eye is clearly evident on the Bermuda radar. Satellite and radar data also show a moat-like area of low precipitation between the eyewall and a large band of convection farther removed from the center. This outer band is expected to affect Bermuda or the waters just east of the island over the next several hours. Observations from an Air Force Hurricane Hunter aircraft indicate that the central pressure has changed little since yesterday. Flight-level winds from the aircraft were as high as 95 kt, but the peak SFMR-observed surface winds were only 69 kt. This again indicates that in this case the strong winds aloft are not being transported to the surface as effectively as in a typical hurricane at lower latitudes. Blending these data results in an intensity estimate of 80 kt for this advisory. This is just a little higher than the latest subjective Dvorak estimates from TAFB and SAB.

The hurricane is gradually turning to the right and the initial motion is 340/14 kt. Larry is currently moving around the western side of a deep-layer subtropical anticyclone over the central Atlantic, and is passing east of Bermuda. The flow on the east side of a strong mid-level trough moving from the northeastern United States to Atlantic Canada will cause Larry to turn toward the northeast and accelerate in 24 to 48 hours. Larry will move near or over southeastern Newfoundland in 36 to 48 hours, and then move over the far north Atlantic around the end of the forecast period. There is very little change to the NHC track forecast from the previous advisory, which remains close to the various consensus model solutions.

Larry is likely remain over warm waters with low shear for another 24 hours or so. Thus the system will probably maintain much of its intensity into Friday. By Friday night and over the weekend, cooler SSTs and increasing shear should cause weakening. However, baroclinic forcing associated with the trough to the west of the hurricane could slow the weakening process. The official intensity forecast keeps Larry at hurricane-force through 48 hours even as it undergoes extratropical transition. In 3-4 days, the global models show Larry merging with another large extratropical cyclone over the north Atlantic.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda later today, and tropical storm conditions are expected there today, along with a risk of coastal flooding.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland Friday night or early Saturday morning as it undergoes transition to a hurricane-force post-tropical cyclone. Hurricane conditions are storm surge are possible in portions of southeastern Newfoundland where a hurricane watch is in effect. Interests there should monitor updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  09/1500Z 32.0N  61.6W   80 KT  90 MPH - Category 1 (ESE St. George's,Bermuda)
 12H  10/0000Z 34.5N  62.2W   80 KT  90 MPH - Category 1 (ENE St. George's,Bermuda)
 24H  10/1200Z 39.0N  60.8W   80 KT  90 MPH - Category 1 (ESE New York,NY)
 36H  11/0000Z 44.8N  56.1W   75 KT  85 MPH - Category 1 (ESE Sydney,NS Canada)
 48H  11/1200Z 51.3N  49.1W   65 KT  75 MPH - Post Tropical (ESE St. Anthony,NF Canada)
 60H  12/0000Z 57.0N  43.5W   60 KT  70 MPH - Post Tropical (ESE Nanortalik,Greenland)
 72H  12/1200Z 61.0N  40.0W   55 KT  65 MPH - Post Tropical (WSW Reykjavik,Iceland)
 96H  13/1200Z...MERGED

NWS National Hurricane Center Miami FL 1100 PM AST Wed Sep 08, 2021 

The infrared satellite presentation of Larry this evening is giving the false impression of a well-organized hurricane, with a ring of colder cloud tops (-65 to -70 C) and a warm spot within. However, we are fortunate to have in-situ data provided by an Air Force Reconnaissance Hurricane Hunter mission investigating Larry this evening. Their observations show that Larry’s center is actually southwest of the warm spot seen on satellite. In fact, the plane was unable to identify an eye with Larry, and the highest flight-level and SFMR winds were found nearly 80 nautical miles away from the center. Moreover, there remains a large discrepancy between the peak 700-mb flight level winds (108-kt) versus the much lower SFMR peak values (67-kt). This suggests that the 90 percent reduction factor that is typically applied to 700-mb flight level winds in the eyewall may not be appropriate for this hurricane given its very large radius of maximum winds more associated with weaker outer convection. Given these factors, the latest NHC initial intensity has been lowered to 85 kt for this advisory. This intensity is also a good compromise between the SAB and TAFB subjective Dvorak estimates.

The hurricane’s heading is still off to the northwest with the latest motion at 330/14 kt. The track forecast philosophy has not changed much for the last few days, with Larry moving around the western periphery of a deep-layer subtropical anticyclone over the central Atlantic. The hurricane should make its closest approach to the east of Bermuda tomorrow as it gradually turns north-northwest and north. After that, the hurricane will begin to dramatically accelerate to the northeast as Larry is picked up by a deep-layer trough moving offshore of the eastern United States. The latest forecast track is quite similar to the previous one, and takes Larry across the southeast portion of Newfoundland in 48-60 hours. The official forecast remains close to the tightly clustered track guidance consensus.

The current structure of Larry appears to be somewhat tilted with height, with the low-level center identified by recon located to the southwest of the apparent center on IR satellite. While the shear as diagnosed by SHIPS appears to be lower, it appears dry air has significantly disrupted Larry’s inner core structure, to the point that it likely will be unable to take advantage of the more favorable conditions. The latest NHC intensity forecast is lower than the previous one, owing to the lower initial intensity, but begins to show more pronounced weakening after 24 hours when the hurricane will accelerate poleward of the northern wall of the Gulf Stream. However, Larry is still forecast to be a hurricane as it passes near or over Newfoundland, though likely beginning to undergo extratropical transition. The models continue to maintain Larry as a large formidable cyclone after extratropical transition is complete while it moves into the far north Atlantic east of Greenland. This cyclone will eventually merge with another extratropical cyclone by the end of the forecast period.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are expected there on Thursday, along with a risk of coastal flooding. A Tropical Storm Warning is in effect for Bermuda, and interests there should closely monitor the latest forecast updates.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it undergoes transition to a hurricane-force post-tropical cyclone. There is an increasing risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 29.7N  60.3W   85 KT 100 MPH - Category 2 (ESE St. George's,Bermuda)
 12H  09/1200Z 31.5N  61.5W   85 KT 100 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  10/0000Z 34.9N  62.3W   85 KT 100 MPH - Category 2 (ESE St. George's,Bermuda)
 36H  10/1200Z 39.3N  60.8W   80 KT  90 MPH - Category 1 (ESE New York,NY)
 48H  11/0000Z 45.2N  55.8W   75 KT  85 MPH - Category 1 (ESE Sydney,NS Canada)
 60H  11/1200Z 51.6N  48.2W   70 KT  80 MPH - Post Tropical (ESE St. Anthony,NF Canada)
 72H  12/0000Z 57.4N  41.6W   65 KT  75 MPH - Post Tropical (ESE Nanortalik,Greenland)
 96H  13/0000Z 63.8N  35.6W   55 KT  65 MPH - Post Tropical (WSW Reykjavik,Iceland)
120H  14/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Wed Sep 08, 2021

Larry’s overall organization has shown little change on satellite images this afternoon. The eye remains rather ill-defined but the hurricane continues to produce some strong convection near/around the center. Cirrus-level outflow remains quite well defined, particularly to the northwest. The current intensity estimate is held at 95 kt, which is only slightly above the latest Dvorak estimates. Another Air Force Reserve Unit Hurricane Hunter aircraft is scheduled to investigate Larry this evening to provide a new intensity estimate.

The hurricane continues heading a little faster toward the northwest, or at about 325/13 kt. The track forecast philosophy remains about the same as before. Larry should move around the western side of a deep-layer subtropical anticyclone over the central Atlantic for the next 36 to 48 hours, passing east of Bermuda tomorrow. After that, the hurricane is expected to accelerate northeastward on the east side of a deep-layer trough moving through the eastern United States, and Larry will move near or over southeastern Newfoundland in roughly 60 hours. Then, the cyclone is forecast to move over the far north Atlantic. The official forecast is close to the dynamical model consensus solution and, again, very similar to the previous NHC track.

Based on the dynamical model guidance, weak to moderate vertical shear should prevail over Larry during the next couple of days. Sea surface temperatures below the cyclone begin to cool significantly after 48 hours, which should induce weakening. However, baroclinic forcing associated with the trough to the west may help the hurricane maintain some of its intensity over cooler waters, as suggested by the global models. The official intensity forecast follows the model consensus and keeps Larry at hurricane strength even after extratropical transition. In 5 days or less, the system should merge with another large cyclonic circulation over the north Atlantic.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are expected there there Thursday, along with a risk of coastal flooding. A Tropical Storm Warning is in effect for Bermuda, and interests there should closely monitor the latest forecast updates.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it undergoes transition to a hurricane-force post-tropical cyclone. There is an increasing risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  08/2100Z 28.9N  59.2W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 12H  09/0600Z 30.6N  60.5W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  09/1800Z 33.3N  61.8W   95 KT 110 MPH - Category 2 (ENE St. George's,Bermuda)
 36H  10/0600Z 37.0N  61.5W   90 KT 105 MPH - Category 2 (ENE St. George's,Bermuda)
 48H  10/1800Z 42.0N  58.5W   85 KT 100 MPH - Category 2 (ESE Shelburne,NS Canada)
 60H  11/0600Z 48.0N  52.0W   75 KT  85 MPH - Post Tropical (ESE Red Head Cove,NL,Canada)
 72H  11/1800Z 54.0N  45.0W   65 KT  75 MPH - Post Tropical (ESE Nanortalik,Greenland)
 96H  12/1800Z 62.0N  37.0W   50 KT  60 MPH - Post Tropical (ESE Kulusuk,Greenland)
120H  13/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Wed Sep 08 2021 

Larry’s eye has been only faintly apparent on recent satellite imagery, but the hurricane is still maintaining a fair amount of deep convection near/around the center. An Air Force Reserve Unit Hurricane Hunter aircraft investigated Larry a little while ago and observations found that the central pressure has risen only slightly since yesterday, with peak flight level winds of 118 kt in the northeastern quadrant. However, the highest SFMR-observed surface winds were only 75 kt, indicating that the strong winds aloft are not very effectively being transported to the surface. Given this, along with the slightly-degraded appearance of the system, the current intensity is reduced to 95 kt, which is just a bit above the latest subjective and objective Dvorak estimates.

The hurricane is moving northwestward at a slightly faster clip, or 320/11 kt. Over the next 36 to 48 hours, Larry is expected to move around the western periphery of a subtropical high pressure area and pass to the east of Bermuda. Thereafter, the cyclone should accelerate northeastward ahead of a deep-layer trough moving through the northeastern United States and become embedded within the mid-latitude southwesterly flow. This will take Larry near or over southeastern Newfoundland in 60-66 hours and then over the far North Atlantic. The official forecast track has not changed significantly from those in the previous few advisories, and remains close to the dynamical model consensus, TVCA.

Larry should remain in an environment of low vertical shear and warm surface waters for the next 36-48 hours. However, the oceanic heat content beneath the hurricane should be gradually decreasing during the next few days. Only slow weakening is forecast, similar to the latest NOAA corrected consensus, HCCA, prediction. In about 72 hours, the global models indicate that Larry will become embedded within a frontal zone, so the NHC forecast shows it as an extratropical cyclone by that time. In 5 days or less, the system is expected to merge with another large cyclone at high latitudes.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas and Bermuda. Significant swells will begin to reach the east coast of the United States and Atlantic Canada later today and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are expected there there Thursday, along with a risk of coastal flooding. A Tropical Storm Warning is in effect for Bermuda, and interests there should closely monitor the latest forecast updates.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it undergoes transition to a hurricane-force post-tropical cyclone. There is an increasing risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 27.7N  58.3W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 12H  09/0000Z 29.1N  59.6W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  09/1200Z 31.6N  61.3W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 36H  10/0000Z 34.7N  61.9W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 48H  10/1200Z 39.1N  60.4W   85 KT 100 MPH - Category 2 (ENE St. George's,Bermuda)
 60H  11/0000Z 44.4N  55.6W   80 KT  90 MPH - Category 1 (ESE Sydney,NS Canada)
 72H  11/1200Z 50.5N  49.0W   65 KT  75 MPH - Post Tropical (ENE St. John's,NF Canada)
 96H  12/1200Z 61.0N  37.0W   60 KT  70 MPH - Post Tropical (ENE Aappilattoq,Greenland)
120H  13/1200Z...MERGED

NWS National Hurricane Center Miami FL 1100 PM AST Tue Sep 07, 2021 

Larry’s eye has become a little better defined since the previous advisory, and the eyewall convective cloud tops have cooled, with a nearly solid ring of -65C to -70C now surrounding the eye. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the central pressure has risen slightly to 966-968 mb and that peak 700-mb flight-level winds measured were 106 kt in the northeast quadrant. These data would suggest that the intensity has decreased a little to 95-96 kt. However, the peak flight-level wind of 106 kt was measured in the wake of a strong eyewall convective burst, suggesting that stronger winds could have been present in that convection. Also, if the surrounding eyewall convective ring closes off during the nocturnal convective maximum period in another six hours, then Dvorak intensity estimates would increase from the current T5.0/90 kt to T5.5/102 kt. Thus, Larry’s intensity has been maintained at 100 kt for this advisory in order to avoid possible intensity vacillations.

The initial motion estimate is 325/10 kt, based on reconnaissance aircraft fixes over the past 12 hours. There remains no significant change to the track forecast or reasoning over the past 48 hours. The latest NHC model guidance remains in strong agreement on Larry continuing to move northwestward and then northward around the western periphery of a deep-layer subtropical ridge during the next 48 hours or so. After passing east of Bermuda by early day 3, the hurricane is forecast to accelerate northeastward and move into the mid-latitude westerlies ahead of a large, eastward-moving trough that is currently approaching the northeastern United States and Atlantic Canada. By day 5, Larry is expected to move across the far north Atlantic. The new NHC track forecast is similar to the previous advisory track, and lies along the eastern edge of the tightly packed simple- and corrected-consensus track models.

Larry’s upper-level outflow pattern remains impressive, and has even expanded and accelerated on the east side owing to a southward-digging upper-level trough, which has enhanced the outflow in that part of the hurricane. The vertical wind shear affecting Larry is expected to remain low for the next 24 hours or so while the hurricane passes over even warmer sea-surface temperatures (SST) approaching 29.7 deg C, even though the oceanic heat content will be decreasing. However, entrainment of dry mid-level air along with eye fluctuations are expected to offset the warmer SSTs. Thus, a slow but steady decrease in intensity through 48-60 hours is expected. Late in the forecast period, colder waters and increasing southwesterly vertical wind shear exceeding 30 kt should induce a faster rate of weakening. By 96-120 hours, the global models also indicate Larry will be merging with a frontal zone. Therefore, the new intensity forecast continues to show extratropical transition during that time period. The official intensity forecast is similar to the previous advisory, and closely follows the simple- and corrected-consensus intensity models IVCN and NOAA-HCCA.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch is in effect for Bermuda and interests there should closely monitor the latest forecast updates.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it transitions to a hurricane-force post-tropical cyclone. There is a risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor the progress of Larry and updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 25.8N  56.8W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  08/1200Z 27.2N  58.0W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  09/0000Z 29.2N  59.6W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 36H  09/1200Z 31.5N  61.3W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 48H  10/0000Z 34.6N  61.8W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 60H  10/1200Z 39.1N  60.1W   85 KT 100 MPH - Category 2 (ESE St. George's,Bermuda)
 72H  11/0000Z 44.5N  55.7W   80 KT  90 MPH - Category 1 (ESE Shelburne,NS Canada)
 96H  12/0000Z 56.2N  43.6W   65 KT  75 MPH - Post Tropical (ESE North River,NF Canada)
120H  13/0000Z 62.8N  33.6W   50 KT  60 MPH - Post Tropical (ESE Aappilattoq,Greenland)

NWS National Hurricane Center Miami FL 500 PM AST Tue Sep 07, 2021 

After becoming rather ragged-looking in earlier satellite images, Larry’s eye has become a little better defined recently, and the surrounding deep convection is more or less maintaining its strength. Observations from a NOAA Hurricane Hunter aircraft show that the central pressure has fallen slightly, to 965 mb. Peak flight-level winds from the aircraft were 110 kt so the advisory intensity is kept at 100 kt. This is also consistent with a Dvorak Current Intensity number from TAFB.

Larry continues its northwestward motion at about 320/8 kt. The hurricane should move around the western side of a deep-layer subtropical anticyclone during the next 48-60 hours. After passing Bermuda, the system is likely to accelerate northeastward while moving into the mid-latitude westerlies ahead of a trough moving from the northeastern United States to Atlantic Canada, and move into the far north Atlantic by day 5. The official track forecast stays close to the previous NHC prediction, and remains in good agreement the various model consensus solutions.

The hurricane continues to exhibit well-defined upper-level outflow, indicative of weak vertical shear. Over the next couple of days, Larry will be traversing waters of gradually decreasing oceanic heat content. This, combined with some dry mid-level air in the environment, should lead to a gradual decrease in intensity through 48-60 hours. Later in the forecast period, colder waters and strong shear should cause more rapid weakening. By day 4, the global models show Larry merging with a frontal zone. Therefore, the NHC forecast calls for extratropical transition by that time. The official intensity forecast is generally below the statistical-dynamical guidance and above the coupled dynamical hurricane models through 72 hours, but in good agreement with the model consensus aids.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch is in effect for Bermuda and interests there should closely monitor the latest forecast updates.
  • 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it transitions to a hurricane-force post-tropical cyclone. There is a risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor the progress of Larry and updates to the forecast.
FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 25.1N  56.3W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  08/0600Z 26.5N  57.4W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  08/1800Z 28.3N  58.8W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 36H  09/0600Z 30.5N  60.5W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 48H  09/1800Z 33.3N  61.7W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 60H  10/0600Z 36.8N  61.2W   85 KT 100 MPH - Category 2 (ESE St. George's,Bermuda)
 72H  10/1800Z 41.7N  58.2W   80 KT  90 MPH - Category 1 (ESE Shelburne,NS Canada)
 96H  11/1800Z 53.0N  48.0W   65 KT  75 MPH - Post Tropical (ESE North River,NF Canada)
120H  12/1800Z 60.0N  38.0W   50 KT  60 MPH - Post Tropical (ESE Aappilattoq,Greenland)

NWS National Hurricane Center Miami FL 1100 AM AST Tue Sep 07, 2021 (see Tuesday video below)

An Air Force Reserve Unit Hurricane Hunter aircraft investigated Larry a little while ago and found that the hurricane has weakened somewhat. The central pressure has risen to 967 mb, and the eyewall is becoming less well defined. Satellite imagery shows that the eye is still evident but the deep convection has has decreased in coverage and intensity. Using a blend of flight-level and SFMR-observed surface winds from the aircraft gives a current intensity estimate of 100 kt, although this may be generous.

The hurricane continues to move northwestward, or 315/8 kt. Larry is forecast to move around the western periphery of a subtropical anticyclone during the next couple of days. By 72 hours, the system should begin to accelerate northeastward on the eastern side of a mid-tropospheric trough moving through the northeastern United States. Thereafter, Larry should be well-embedded in the higher-latitude southwesterly flow, pass near Newfoundland and move into the far North Atlantic as an extratropical cyclone. The official track forecast is essentially the same as the previous one and in very close agreement with the latest NOAA corrected consensus and Florida State University (FSU) Superensemble tracks.

Larry is in a low-shear environment with fairly well-defined upper-level outflow. However dry mid-level air and possible upwelling of cooler waters beneath the slow-moving circulation appear to be at least partially responsible for weakening. Since the environment does not appear to be very hostile for the next couple of days, only slow weakening is anticipated. The official intensity forecast for the next 48-72 hours lies below the statistical dynamical Decay-SHIPS guidance and above the coupled- HWRF dynamical model prediction. By 96 hours, the FSU cyclone phase analysis indicates that Larry will have undergone an extratropical transition, and this is also shown in the official forecast.

Larry is expected to pass east of Bermuda on Thursday as a large hurricane. Given the expansive size of Larry’s wind field and forecast uncertainties, a Tropical Storm Watch has been issued for the island.

Key Messages:

  • 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry’s large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch is in effect for Bermuda and interests there should closely monitor the latest forecast updates.
FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 24.4N  55.6W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  08/0000Z 25.6N  56.6W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 24H  08/1200Z 27.3N  58.1W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 36H  09/0000Z 29.3N  59.9W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 48H  09/1200Z 31.8N  61.3W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 60H  10/0000Z 34.9N  61.8W   85 KT 100 MPH - Category 2 (ENE St. George's,Bermuda)
 72H  10/1200Z 39.0N  60.0W   80 KT  90 MPH - Category 1 (ESE New York,NY)
 96H  11/1200Z 50.0N  50.0W   65 KT  75 MPH - Post Tropical (ENE Gander,NF Canada)
120H  12/1200Z 58.0N  42.0W   50 KT  60 MPH - Post Tropical (ESE Aappilattoq,Greenland)

NWS National Hurricane Center Miami FL 1100 PM AST Mon Sep 06, 2021 

Larry has changed little in geostationary satellite imagery since the NOAA P-3 aircraft left the storm after 2130 UTC. Data from the mission showed that the hurricane possessed a very large wind field, and there were occasional hints in the flight-level wind data of an outer wind maxima trying to develop. The most recent passive microwave imagery from a 2148 UTC SSMIS pass showed some evidence of secondary bands forming away from the primary eyewall, though the inner eye remains large and distinct. Whether or not this will be the start of another eyewall replacement cycle (ERC) remains to be seen. For now, both the subjective Dvorak estimates from SAB and TAFB remain unchanged from earlier today, so Larry’s intensity has been maintained at 110 kt for this advisory.

The hurricane continues to move to the northwest at 325/9 kt, guided along the southwestern periphery of a prominent subtropical ridge. Larry will reach the westward extent of this ridge in 60-72 hours as a large deep-layer trough approaches from the northeastern United States. The latest guidance now shows this trough capturing Larry towards the end of the forecast period, resulting in an abrupt acceleration to the northeast as the hurricane is steered by the strong westerly flow ahead of the mid-latitude trough. The track guidance continues to be in great agreement with Larry’s forecast track, and only a few minor adjustments were needed to the most recent forecast, staying near the middle of the track guidance envelope. This latest forecast continues to show Larry passing to the east of Bermuda on Thursday. However, given Larry’s large size, some impacts could still be felt even if the center passes well east, and a tropical storm watch could be needed for the island as soon as tomorrow morning.

The intensity forecast for Larry over the next few days is likely to be controlled by changes to its inner-core structure. If another ERC begins soon, this could result in a short-term drop off in maximum sustained winds as the hurricane’s wind field expands. As mentioned last night, the broadening wind field, in combination with Larry’s slow motion currently at 9 kt, could also result in more ocean upwelling closer to Larry’s inner core. While the latest SHIPS guidance depicts warm sea-surface temperatures along the track of Larry over the next 2-3 days, the oceanic heat content in this part of the Atlantic basin is not very high. This might explain why the atmosphere-ocean coupled models (COAMPS-TC, HWRF, HAFS-B) show more significant weakening with a gradually decaying inner-core over cooler upwelled waters. The latest NHC intensity forecast is lower than the previous one, giving a bit more weight to the dynamically coupled hurricane models versus the statistical-dynamical guidance. However, even this latest forecast is higher than the reliable HFIP Corrected Consensus Approach (HCCA). Regardless of these intensity details, Larry is expected to remain a large and powerful hurricane over the next few days.

Key Messages:

  • 1. Large swells generated by Larry are affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda tonight and tomorrow. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. Larry is forecast to approach Bermuda during the next few days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. Interests in Bermuda should closely monitor the latest forecast updates during the next few days, and tropical storm watches could be needed for the island as soon as tomorrow.
FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 23.1N  54.4W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  07/1200Z 24.1N  55.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  08/0000Z 25.6N  56.8W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  08/1200Z 27.3N  58.2W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 48H  09/0000Z 29.2N  59.9W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 60H  09/1200Z 31.6N  61.3W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 72H  10/0000Z 34.6N  61.8W   90 KT 105 MPH - Category 2 (ENE St. George's,Bermuda)
 96H  11/0000Z 44.0N  55.7W   80 KT  90 MPH - Category 1 (ENE Lunenburg,NS Canada)
120H  12/0000Z 55.5N  43.4W   65 KT  75 MPH - Post Tropical (WSW Nanortalik,Greenland)

NWS National Hurricane Center Miami FL 1100 AM AST Mon Sep 06, 2021 

Larry currently has an annular structure, with a 60 n-mi diameter eye and a relatively thick eyewall. High-resolution visible imagery shows several meso-vortices rotating within the eye, which is typically observed in strong hurricanes. The upper-level outflow has become better defined over the western portion of the circulation, indicative of decreased shear in comparison to yesterday. The advisory intensity is kept at 105 kt, in reasonable agreement with the latest Dvorak estimates from TAFB and SAB.

Larry has slowed its forward speed a bit, and is now moving northwestward near 9 kt. There are no important changes in the track forecast or reasoning from the previous advisory. During the next few days, the hurricane is expected to move around the western periphery of a subtropical anticyclone over the central Atlantic, turning northward and northeastward. At this time, Larry is forecast to pass east of Bermuda and make its closest approach to the island on Thursday. Given Larry’s large size, some impacts could be felt even if the center remains well east of the island as forecast. In 3-5 days, the cyclone should accelerate northeastward ahead of a large mid-tropospheric trough moving through the northeastern United States. The official track forecast follows the latest dynamical model consensus, and remains close to the previous one. Since the model guidance is in good agreement, this continues to be a high-confidence track forecast.

Vertical shear is expected to remain low and the system will continue to traverse warm SSTs for the next few days. However, the presence of dry mid-level air and the broad nature of the hurricane’s inner core will probably mitigate against significant restrengthening. Some fluctuations in intensity are possible for the next 48 hours or so. In 3-5 days, cooler waters and increasing shear should cause gradual weakening. Around the end of the forecast period, the global models show the system beginning to merge with a frontal zone near Newfoundland. The official forecast is on the high side of the model guidance suite and close to the latest Decay-SHIPS prediction.

Key Messages:

  • 1. Large swells generated by Larry are affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda today through Tuesday. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. Larry is forecast to approach Bermuda during the next few days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should closely monitor the latest forecast updates during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 22.1N  52.9W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  07/0000Z 23.1N  54.0W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  07/1200Z 24.5N  55.3W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  08/0000Z 25.9N  56.6W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  08/1200Z 27.5N  58.0W  100 KT 115 MPH - Category 3 (ESE St. George's,Bermuda)
 60H  09/0000Z 29.3N  59.6W  100 KT 115 MPH - Category 3 (ESE St. George's,Bermuda)
 72H  09/1200Z 31.6N  61.2W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 96H  10/1200Z 38.6N  60.0W   85 KT 100 MPH - Category 2 (ESE Cape May,NJ)
120H  11/1200Z 49.0N  49.0W   70 KT  80 MPH - Post Tropical (ENE Gander,NF Canada)

NWS National Hurricane Center Miami FL 500 AM AST Mon Sep 06, 2021

Recent microwave data indicate that Larry has likely completed an eyewall replacement cycle (ERC). The 0530 UTC AMSR2 imagery reveals that the hurricane now has a large, single eyewall structure with an eye diameter greater than 50 n mi, in contrast with the concentric eyewall structure noted yesterday. Larry’s large eye appears somewhat ragged in conventional satellite imagery, as some convective debris clouds associated with the old eyewall continue to erode. Earlier scatterometer data confirmed that the 50- and 64-kt wind radii of Larry have broadened, likely as a result of the ERC. Based on a blend of the 102-kt Dvorak estimates from TAFB and SAB and a 107-kt ADT current intensity estimate, the initial intensity is set at 105 kt for this advisory. NOAA aircraft is scheduled to conduct a research mission into Larry later today, which should provide more information about Larry’s structure and intensity.

Larry is moving northwestward, or 305/10 kt. The track forecast for Larry remains of high confidence. The hurricane is expected to continue moving northwestward through midweek along the western periphery of a mid-level subtropical ridge over the central Atlantic. On Thursday, Larry is forecast to turn northward within the flow of an upper-level trough that is expected to move off the coast of the northeastern United States. By Friday, Larry should accelerate northeastward and recurve into the mid-latitudes, passing near or offshore Atlantic Canada. The latest track guidance is tightly clustered once again. Thus, the official NHC track forecast is virtually unchanged from the previous one and remains near the consensus aids HCCA and TVCA. Larry is forecast to pass east of Bermuda and make its closest approach to the island on Thursday. Given Larry’s large size, some impacts could be felt even if the center remains well east of the island as forecast.

The intensity forecast remains more complex. Now that the ERC is likely completed, some strengthening cannot be ruled out in the near-term if the large, consolidated eyewall is able to contract. However, the SHIPS guidance suggests some weak to moderate westerly shear is still present, and Larry’s broad wind field could result in some upwelling of cooler waters that may inhibit intensification. Ultimately, these mixed signals suggest that some intensity fluctuations could occur over the next 24-36 h, and so the NHC intensity forecast shows little net change during this time. Thereafter, only gradual weakening is shown as the large hurricane will remain in a reasonably favorable environment of weak to moderate shear and warm SSTs through the 72-96 h period. By day 5, the cyclone will likely be in the process of extratropical transition, still as a powerful cyclone. Overall, the NHC intensity forecast lies on the higher end of the guidance, between the stronger statistical-dynamical models DSHP/LGEM and the weaker multi-model consensus aids IVCN/HCCA.

Key Messages:

  • 1. Large swells generated by Larry are affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda today through Tuesday. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials this week.
  • 2. Larry is forecast to approach Bermuda during the next few days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should closely monitor the latest forecast updates during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 21.5N  52.4W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  06/1800Z 22.6N  53.6W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  07/0600Z 23.9N  54.9W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  07/1800Z 25.3N  56.2W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  08/0600Z 26.8N  57.5W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  08/1800Z 28.5N  59.0W  100 KT 115 MPH - Category 3 (ESE St. George's,Bermuda)
 72H  09/0600Z 30.6N  60.6W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 96H  10/0600Z 36.7N  61.0W   90 KT 105 MPH - Category 2 (ENE St. George's,Bermuda)
120H  11/0600Z 45.5N  52.0W   75 KT  85 MPH - Category 1 (ENE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Sun Sep 05, 2021

A series of afternoon and evening passive microwave imagery indicate that Larry has evolved from an earlier stable eyewall structure to one with concentric eyewalls. The most recent microwave pass, a 2201 UTC SSMIS overpass, showed that Larry is likely in the latter stages of this most recent eyewall replacement cycle (ERC), with a new outer eyewall radius of nearly 50 nautical miles. However, geostationary satellite imagery still shows quite a bit of inner eyewall convection and it may take a while longer before this ERC is complete. A recent ASCAT-A pass at 2339 UTC also indicated that Larry’s inner-core wind field had expanded further, likely related to this recent ERC. The latest Dvorak intensity estimates from TAFB/SAB remain unchanged from this afternoon, and the initial intensity remains 110 kt this advisory. A NOAA P-3 aircraft will be conducting a research mission into the Larry tomorrow and should provide some helpful in-situ measurements to verify the hurricane’s intensity.

Larry’s motion to the northwest continues to gradually slow down, with the latest estimated motion at 310/10 kt. The forecast track reasoning remains the same. Larry should maintain its northwestward heading for the next 2-3 days as it remains steered around the southern periphery of a mid-level ridge to the hurricane’s northeast. After 72 hours, Larry will be reaching the western extent of this ridge while an amplifying mid-latitude trough will be approaching from the northeastern United States. The combination of these features should help Larry recurve, first to the north, and then northeast with accelerating forward motion by the end of the forecast period. The track guidance continues to be in excellent agreement, and very few changes were made to the track forecast this cycle, staying close to the consensus aids HCCA and TVCA. The intensity forecast with Larry is somewhat tricky. Larry’s wind field continues to grow, following the multiple ERCs that have occurred over the past few days. At the same time, Larry’s forward motion has gradually been slowing down, with the latest estimate down to 10 kts. The combination of Larry’s widening wind field with its slower forward motion opens the storm up to possible upwelling of cooler ocean waters near its inner-core. In fact, a drifting buoy that Larry moved over in the past 24 hours showed a significant drop in sea-surface temperatures from 27.5 C to less than 26 C. These in-situ measurements are helpful, because they are lower than the SHIPS-derived sea-surface temperature values and more consistent with the upwelling recently forecast by the HWRF model. Adding to the forecast complexity is the ongoing ERC which could be ending over the next 6-12 hours.

The latest NHC intensity forecast is similar to the previous one for the first 24 hours, showing little change in intensity after ERC completion. Thereafter, while dynamical conditions near Larry are expected to become more favorable (lower vertical wind shear), the anticipated upwelling from Larry’s large wind field as the storm moves slowly northwestward is forecast to result in gradual decay. The latest NHC intensity forecast is a bit lower than the previous one after 48 hours, following the latest HCCA consensus aid closely. However, Larry’s wind field is also forecast to expand over this time period, making the cyclone a prolific swell and surf producer.

Key Messages:

  • 1. Large swells generated by Larry are already affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda on Monday and Tuesday. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials this week.
  • 2. Larry is forecast to approach Bermuda during the next several days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should closely monitor the latest forecast updates during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 21.0N  51.4W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  06/1200Z 22.0N  52.6W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  07/0000Z 23.2N  54.1W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  07/1200Z 24.6N  55.4W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  08/0000Z 26.0N  56.7W  100 KT 115 MPH - Category 3 (ESE St. George's,Bermuda)
 60H  08/1200Z 27.6N  58.2W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)
 72H  09/0000Z 29.4N  59.9W   90 KT 105 MPH - Category 2 (ESE St. George's,Bermuda)
 96H  10/0000Z 34.4N  61.6W   85 KT 100 MPH - Category 2 (ENE St. George's,Bermuda)
120H  11/0000Z 42.9N  55.8W   80 KT  90 MPH - Category 1 (ESE Newellton,NS Canada)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Sep 05, 2021 

Larry continues as a large and intense hurricane this morning, with a 40 n mi diameter eye surround by cloud tops to near -80 deg C. There are, however, some breaks in the cold tops over the northern portion of the circulation. The current intensity is adjusted slightly to 110 kt, based on a blend of subjective Dvorak estimates from TAFB and SAB along with objective ADT estimates from UW-CIMSS. Upper-level outflow remains somewhat restricted over the southwestern quadrant of the system, indicative of at least slight vertical shear. This shear is probably being caused by the flow to the east of an upper-level low to the north of Puerto Rico. The low is forecast to move northwestward over the next few days, possibly lessening the shear over Larry.

The hurricane is moving northwestward at a slightly slower speed, or 310/11 kt. Larry is likely to continue its northwestward trek along the southwestern periphery of a mid-tropospheric anticyclone during the next 2-3 days, with only a slight reduction in forward speed. Around 96 hours, the hurricane is forecast to turn toward the north-northwest and north while rounding the western side of the ridge. By the end of the forecast period, Larry is expected to begin its recurvature into the mid-latitude westerlies. The new official forecast track essentially follows the previous one, and is also very close to the latest NOAA corrected consensus and Florida State University Superensemble guidance.

Larry’s large eye suggests that no rapid changes in strength are likely during the short term. Since vertical shear is not expected to increase and the system will be traversing warm waters, the hurricane should be able to more or less maintain its intensity during the next few days. One inhibiting factor is the presence of relatively dry mid-level air in the environment. The official intensity forecast is on the high side of the model guidance and keeps Larry as a major hurricane through 72 hours.

Key Messages:

  • 1. Large swells generated by Larry are expected to reach the Lesser Antilles today and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda on Monday and Tuesday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by midweek. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials this week.
  • 2. Larry is forecast to approach Bermuda during the next several days, likely as a major hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should closely monitor the latest forecast updates during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 19.5N  49.7W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  06/0000Z 20.5N  51.1W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  06/1200Z 21.9N  52.7W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  07/0000Z 23.0N  54.0W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  07/1200Z 24.3N  55.4W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  08/0000Z 25.7N  56.7W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)
 72H  08/1200Z 27.3N  58.1W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)
 96H  09/1200Z 31.1N  61.1W   95 KT 110 MPH - Category 2 (ENE St. George's,Bermuda)
120H  10/1200Z 37.4N  60.6W   85 KT 100 MPH - Category 2 (ENE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Sat Sep 04, 2021 

Larry has developed a large eye this evening that is 40-45 n mi in diameter, and the surrounding cloud tops have warmed somewhat. There have been no microwave passes over the hurricane for quite some time to assess its structure, but conventional satellite images suggest that Larry has taken on some annular characteristics (and the objective screening algorithm tagged it as marginally annular). Dvorak CI numbers and objective estimates are all between 100-102 kt, so Larry’s initial intensity is lowered slightly to 105 kt. Larry’s motion remains west-northwestward (300 degrees) at 12 kt.

The hurricane is expected to turn northwestward tonight or early Sunday around the southwestern periphery of a mid-level high centered over the central Atlantic, and then maintain that heading with some decrease in forward speed through day 4. By day 5, Larry should turn northward and accelerate between the high and an approaching deep-layer trough over the eastern United States. The updated NHC track forecast is largely unchanged from the previous advisory and is of high confidence since there is lower-than-normal spread among the track models. Larry is forecast to make its closest approach to Bermuda in 4 to 5 days while it recurves around the ridge, but despite the high-confidence forecast, there is still uncertainty on how close that approach will be since several GEFS and ECMWF ensemble members bring Larry’s center very close to or over the island. Even with a track east of the island, Larry will be large enough to possibly cause some impacts on Bermuda. Water vapor imagery shows some restriction to the outflow in the southwestern quadrant, which could be indicative of some shear.

There continues to be some discrepancy among the models on how much shear the hurricane will contend with as it approaches a mid-/upper-level trough located north of the Leeward Islands. The GFS keeps the shear over Larry fairly low since it’s farther from the trough, while the ECMWF increases the shear to moderate or strong levels during the next 48 hours. If Larry reaches the area of stronger shear, its intensity would obviously be adversely affected. In terms of structure, significant re-intensification is now less likely since Larry has such a large eye and an expanding wind field. On the positive side, the hurricane will be moving over gradually warmer waters for the next 3 days or so. Given these conflicting factors, the updated NHC intensity forecast allows for some slight restrengthening in the short term but then keeps Larry’s intensity steady for the next 3 days. Many of the intensity models are even lower than what’s shown in this forecast, so additional adjustments may be required in future advisories.

Key Messages:

  • 1. Large swells generated by Larry are expected to first reach the Lesser Antilles on Sunday and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda Monday and Tuesday. Significant swells will likely reach the east coast of the United States and Atlantic Canada around midweek. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming week.
  • 2. Larry is forecast to approach Bermuda during the next several days, possibly as a major hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of next week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should monitor changes to the forecast during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  05/0300Z 18.0N  48.0W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  05/1200Z 19.1N  49.5W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  06/0000Z 20.5N  51.3W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  06/1200Z 21.7N  53.0W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  07/0000Z 23.0N  54.5W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  07/1200Z 24.2N  56.0W  110 KT 125 MPH - Category 3 (ESE St. George's,Bermuda)
 72H  08/0000Z 25.8N  57.5W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)
 96H  09/0000Z 29.4N  60.5W  100 KT 115 MPH - Category 3 (ENE St. George's,Bermuda)
120H  10/0000Z 35.1N  61.4W   90 KT 105 MPH - Category 2 (ENE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Sat Sep 04, 2021 

Larry remains a formidable hurricane this afternoon. Both visible and infrared satellite bands show the hurricane has a well-defined and warm eye (greater than 10 C) surrounded by a cold ring of eyewall convection (-60 to -70 C). An AMSR2 microwave pass received at 1630 UTC showed the well-defined eye of Larry, though the 89 GHz channel hinted that the eyewall was weaker on its eastern side. Taking a look at the high-density atmospheric motion vectors (AMVs), available thanks to a GOES-16 1-minute updating domain over Larry, there is some restriction of Larry’s outflow to the southwest.

Flight-level wind data from the NASA-DC8 aircraft conducting a research mission around Larry also showed some light southwesterly flow between 10-20 kt just a few degrees to the south and west of the storm center. These data suggest that the upper-level wind environment is not as pristine as earlier suggested by SHIPS guidance, with the southwesterly flow likely restricting Larry’s outflow in that quadrant. The SAB/TAFB subjective Dvorak intensity estimates are unchanged from this morning, and the latest UW-CIMSS ADT and SATCON estimates have also plateaued in the 105-110 kt range. Therefore, Larry was maintained as a 110 kt hurricane this advisory. Larry remains on a west-northwest track this afternoon, but a bit slower at 300/12 kt. There has been little change to the track philosophy over the next several days, as the guidance is in good agreement that Larry will maintain a continued west-northwest heading while gradually slowing down as it rounds the southern periphery of a large mid-level ridge.

However, there has been a notable eastward shift in the track guidance in the short-term. The latest ECMWF run, which had previously been on the southwest side of the track guidance envelope, is now very similar or even a tad east of the latest GFS run. This shift has also resulted in an eastward adjustment in the consensus aids this afternoon. The latest NHC track forecast was adjusted a bit to the right early on, but not as far right as the HCCA and TVCA aids. After 72 hours, the track guidance actually converges very close to the previous track forecast, and few changes were needed after this time period. Based on this forecast, Larry will continue moving across the central Atlantic in the coming days, and be approaching Bermuda from the southeast in the day 4 to 5 forecast period.

The existence of some light upper-level southwesterly flow ahead of Larry today was bit of a surprise, since the SHIPS guidance from the last few days suggested the shear-vector would be out of the east and weak. Indeed, the latest ECMWF-SHIPS guidance now shows moderate southwesterly vertical wind shear beginning earlier, and peaking between 20-25 knots in 36 to 48 hours. While the GFS-SHIPS shear remains much lower, given what I’m seeing from the latest upper-level flow in front of Larry, the ECMWF seems closer to correct. For this reason, the latest NHC intensity guidance now shows a bit of weakening after 24 hours, when the shear magnitude is expected to peak as the hurricane interacts with a large tropical upper-tropospheric trough (TUTT) located to its northwest.

However, Larry has a large and vertically-deep circulation, and ultimately it will win the battle against the more vertically shallow TUTT, which is forecast to cut off and move away from the hurricane’s expansive upper-level outflow. By 60 hours, this change in the synoptic pattern should once again reduce the vertical wind shear over Larry, and it will have a chance to achieve a secondary peak between the 60-84 hour time-frame. However, eyewall replacement cycles could also occur at any time over the next 2-5 days, providing additional intensity fluctuations that make this a challenging intensity forecast. The latest NHC intensity forecast is lower than the previous one, but still remains higher than the latest HCCA consensus aid. Regardless of the details, Larry is expected to remain a large major hurricane over the next 3-4 days.

Key Messages:

  • 1. Large swells generated by Larry are expected to first reach the Lesser Antilles on Sunday and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda Monday and Tuesday. Significant swells will likely reach the east coast of the United States and Atlantic Canada around midweek. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming week.
  • 2. Larry is forecast to approach Bermuda during the next several days, possibly as a major hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of next week. While it is too soon to determine the magnitude of these hazards and potential impacts on Bermuda, interests there should monitor changes to the forecast during the next several days.
FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 17.4N  47.1W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  05/0600Z 18.4N  48.6W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 24H  05/1800Z 19.8N  50.6W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 36H  06/0600Z 21.0N  52.3W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 48H  06/1800Z 22.2N  54.0W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  07/0600Z 23.4N  55.6W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 72H  07/1800Z 24.7N  57.0W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  08/1800Z 28.3N  59.9W  110 KT 125 MPH - Category 3 (ESE St. George's,Bermuda)
120H  09/1800Z 33.4N  61.9W   95 KT 110 MPH - Category 2 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 04, 2021

Overnight and this morning, Larry appears to have gone through a rather quick eyewall replacement cycle (ERC). The most recent 1000 UTC GMI microwave pass suggests that Larry now has a much larger eye and surrounding eyewall, with less evidence of concentric bands as noted yesterday. On geostationary satellite the larger eye is also becoming apparent on visible and infrared channels, though some left over inner eyewall debris remains. Consistent with the larger eye, an ASCAT-B pass received at 1226 UTC indicated that the 34-, 50-, and 64-kt wind radii have expanded with Larry this morning. While the most recent SAB and TAFB subjective Dvorak intensity estimates have remain at 90 kt and 100 kt respectively, the objective estimates are higher, with an earlier UW-CIMSS SATCON estimate up to 112 kt, though it has recently been adjusted lower. With the eye beginning to clear out on the most recent satellite images, I am favoring the higher objective estimates, bringing Larry up to 110 kt for this advisory. Larry’s track has remained fairly steady toward the west-northwest, but just a touch slower and more poleward with the latest estimated motion at 300/13 kt.

This west-northwest motion is expected to continue for the next several days with only a very gradual poleward bend as Larry remains positioned to the south of an expansive mid-level ridge extending westward ahead of Larry’s expected path. As has been the case the last several days, the track guidance is in excellent agreement over the next 36-48 hours with more spread becoming apparent thereafter. As discussed yesterday, the increase in spread in the latter portion of the forecast appears to be related to how much mid-level ridging stays north of Larry. The ECMWF and its ensembles maintain more ridging that results in a slower and more westward track, while the GFS and its ensembles place more ridging east of Larry that results in a faster more eastward track. The UKMET favors a solution closer to the ECMWF while the Canadian favors a solution closer to the GFS. For now, the latest NHC track has elected to remain close to the HFIP corrected consensus approach (HCCA) which slightly favors the ECMWF solution over the GFS.

This latest track forecast is quite similar to the previous one, but just a touch slower. Based on this forecast, Larry will continue moving across the central Atlantic in the coming days, and be approaching the latitude of Bermuda by the end of the forecast period. Conditions continue to remain favorable for additional intensification over the next few days, with vertical wind shear remaining under 10 kts, sea-surface temperatures gradually increasing, and mid-level relatively humidity staying fairly moist.

However, by 48 hours, Larry will be impinging on the eastern edge of a large upper-level mid-oceanic trough, which could result in an increase in westerly vertical wind shear over the hurricane. However, the models handle Larry’s interaction with this synoptic feature differently. The GFS suggests this upper-level trough will fracture to the west fairly quickly, keeping a more favorable upper-level pattern over Larry, while the ECMWF has a stronger trough that takes longer to give way to Larry’s upper-level outflow, providing more westerly shear over the hurricane. Additional eyewall replacement cycles are also possible in the coming days, which could result in additional intensity fluctuations that are challenging to predict ahead of time. For now, the latest NHC intensity forecast keeps Larry intensifying over the next 24-36 hours, with only a very gradual decay thereafter due to the somewhat less favorable dynamical environment. The latest intensity forecast remains on the high end of the guidance, noting that there still remain higher outliers making Larry stronger than the 125 kt peak intensity (HAFS-B, COAMPS-TC).

Regardless of the details, Larry is expected to remain a large major hurricane through the forecast period. Significant ocean swells generated by Larry’s growing wind field are expected to reach the Lesser Antilles tomorrow, and then spread westward to portions of the Greater Antilles, the Bahamas, and Bermuda on Monday and Tuesday. These swells could cause life-threatening rip currents and high surf conditions. Large swells are also likely to spread to the east coast of the United States by midweek.

ORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 16.8N  45.8W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  05/0000Z 17.7N  47.5W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 24H  05/1200Z 19.1N  49.6W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 36H  06/0000Z 20.3N  51.5W  125 KT 145 MPH - Category 4 (ENE Codrington,Barbuda)
 48H  06/1200Z 21.5N  53.2W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  07/0000Z 22.6N  54.8W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  07/1200Z 23.8N  56.4W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  08/1200Z 27.0N  59.4W  110 KT 125 MPH - Category 3 (ESE St. George's,Bermuda)
120H  09/1200Z 31.6N  62.0W  100 KT 115 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Fri Sep 03, 2021 

Larry has had a distinct but slightly ragged 15 n mi wide eye during the past few hours, while convective cloud tops within the eyewall have been gradually cooling. Intensity estimates have responded, somewhat significantly, to the improved structure, and TAFB and SAB Dvorak fixes at 0000 UTC were T5.5/102 kt and T5.0/90 kt, respectively. In addition, objective UW-CIMSS ADT and SATCON estimates are near 105 kt. Larry has become a major hurricane, the third of the Atlantic season, with estimated 100-kt sustained winds.

The hurricane is located due south of a mid-tropospheric high centered over the central Atlantic, and continues to move toward the west-northwest (285/14 kt). Larry is generally expected to move around the southwestern periphery of the high, turning northwestward at a slower speed by Sunday and then north-northwestward by Wednesday as a deep-layer trough moves eastward across the eastern United States. There is fairly high confidence in the track forecast, with model guidance showing a below- to near-normal amount of spread through day 5. The new NHC track forecast is right along the forecast from the previous advisory through day 3, and then nudged slightly westward on days 4 and 5. It should be noted that a few of the consensus aids, including HCCA, are still a little bit west of the official forecast at day 5, which might portend additional westward nudges in future advisories.

By strict definition, Larry hasn’t quite rapidly intensified since this time yesterday, but it has still strengthened quickly over waters that are considered only marginally warm (26-27 degrees Celsius). For the next couple of days, low shear, higher oceanic heat content, and a more unstable environment should favor additional intensification. However, there are still indications that Larry could run into an environment of higher shear and less upper-level divergence in 2-3 days as it approaches a mid-/upper-level trough currently located north and northeast of the Leeward Islands. In addition, internal processes within the hurricane’s core itself, such as eyewall replacement cycles, could affect the intensity. In light of all these factors, the NHC intensity forecast relies on persistence to show additional strengthening during the next 36 hours, and then holds Larry steady through 60 hours at an intensity that is near the upper end of the guidance. Very gradual weakening is anticipated on days 3 through 5 while Larry heads in the direction of higher latitudes, yet the hurricane is forecast to remain at major hurricane intensity for the entire 5-day forecast period.

Significant ocean swells generated by Larry’s growing wind field are expected to reach the Lesser Antilles on Sunday, and then spread westward to portions of the Greater Antilles, the Bahamas, and Bermuda on Monday and Tuesday. These swells could cause life-threatening rip currents and high surf conditions. Large swells are also likely to spread to the east coast of the United States by midweek.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 15.5N  43.3W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 12H  04/1200Z 16.2N  45.3W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 24H  05/0000Z 17.4N  47.6W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 36H  05/1200Z 18.7N  49.7W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 48H  06/0000Z 20.0N  51.7W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  06/1200Z 21.2N  53.6W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  07/0000Z 22.4N  55.3W  115 KT 130 MPH - Category 3 (ESE St. George's,Bermuda)
 96H  08/0000Z 25.4N  58.5W  115 KT 130 MPH - Category 3 (ESE St. George's,Bermuda)
120H  09/0000Z 29.5N  61.5W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Fri Sep 03, 2021 

Over the course of the day, Larry’s appearance has become more impressive. The eye has been gradually becoming better defined on visible satellite imagery as the center cloud top temperature has been warming on the infrared channel. Several microwave passes have been received since the last advisory. The most recent pass at 1900 UTC suggested the eye and surrounding eyewall convection is becoming better defined, though still weaker on the east side. 1800 UTC subjective Dvorak classifications were still both CI 4.5/77 kt from TAFB and SAB. However, the objective satellite estimates have been rising quickly, with the most recent UW-CIMSS SATCON estimate up to 84 kt. Thus, the NHC advisory intensity has been raised to 85 kt for this advisory, making Larry a category 2 hurricane.

Larry’s motion has remained fairly steady to the west-northwest throughout the day, at 285/14 kt. The latest track reasoning remains unchanged, with Larry being steered to the west-northwest around the southern periphery of an expansive mid-level ridge centered north of the hurricane. This ridge axis will gradually become oriented to the northeast of Larry with time, allowing the tropical cyclone to gradually gain more latitude. Because the ridge is quite large, even as its axis shifts eastward, a portion of the ridge will still remain to the north of the storm. The end result is that Larry should only slowly gain a more poleward component of motion as the system also gradually slows down. While the track guidance spread remains small for the first 48-60 hours of the forecast, a bit more longitudinal spread becomes apparent thereafter, which appears related to how much mid-level ridging remains poleward of the cyclone. The latest 12z ECMWF run has a distinctly stronger ridge, oriented more poleward in comparison to the 12z GFS run. Thus, it is not surprising to see that the ECMWF track is a bit further west and slower than the GFS. The latest NHC track forecast this cycle was also adjusted a bit slower, following the TVCN and HCCA consensus aids. However, it is interesting to note the latest 12z ECMWF ensembles are even slower than this track forecast, and future slower adjustments may be needed if these track solutions verify.

It remains too soon to determine what impacts Larry may pose to the Island of Bermuda, but interests there should monitor updates in the forecast in the subsequent days. With the recent improvement in Larry’s structure on satellite imagery, the hurricane may be starting another rapid intensification (RI) cycle, as suggested by the high RI probabilities given in the DTOPS guidance. However, the earlier microwave data also suggested that there were a lot of concentric bands outside of the primary eyewall, and it is not out of the question that another eyewall replacement cycle could begin in the next 24-36 hours. Instead of attempting to forecast these often stochastic processes, the latest NHC intensity forecast will instead show a healthy rate of deepening over the next several days, now taking Larry to 120 kt in 48 hours.

Afterwards, there still remain questions as to how much the vertical wind shear will increase over Larry, with the ECMWF-SHIPS indicating higher shear that could affect Larry’s inner-core structure, while the GFS-SHIPS showing much lower shear. Warmer sea-surface temperatures also await the hurricane in the 60-96 hour period. Due to these competing factors, the intensity forecast during this period will only show very gradual weakening. The latest NHC intensity forecast remains on the high end of the guidance, but still remains lower than the higher HAFS-B and COAMPS-TC models. It should be noted that the majority of the guidance also shows Larry becoming a very large hurricane, with a significant expansion of the 34-, 50-, and 64-kt wind radii also forecast.

Significant ocean swells generated by the increasingly large wind field of Larry are expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and high surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well.

FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 15.0N  42.0W   85 KT 100 MPH - Category 2 (ESE Praia,Cape Verde)
 12H  04/0600Z 15.8N  44.1W   95 KT 110 MPH - Category 2 (ESE Praia,Cape Verde)
 24H  04/1800Z 16.9N  46.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  05/0600Z 18.1N  48.7W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  05/1800Z 19.4N  50.8W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  06/0600Z 20.7N  52.8W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  06/1800Z 21.9N  54.5W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  07/1800Z 24.7N  57.6W  115 KT 130 MPH - Category 3 (ESE St. George's,Bermuda)
120H  08/1800Z 28.7N  60.5W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Fri Sep 03, 2021 

Larry continues to have the presentation of a hurricane that is gradually becoming better organized. Its structure this morning consists of well defined spiral banding around a somewhat asymmetric central dense overcast. More recently, a warm spot appears to be forming on both infrared and visible satellite channels which could foreshadow the development of a better-defined eye, as hinted at on an earlier 0934 UTC SSMIS microwave pass. The most recent subjective Dvorak classifications at 1200 UTC were still CI 4.5/77 kt from TAFB and SAB. Interestingly, the objective satellite estimates from ADT and SATCON remain on the lower side, though these seem conservative given the structural improvements seen on recent satellite images. Favoring the subjective estimates, the initial intensity is being maintained at 80 kt for this advisory. Larry continues to move to the west-northwest at 285/14 kt. A prominent mid-level ridge located to the north of the hurricane is expected to continue this heading over the next 24 to 36 hours, though with a gradual decrease in forward speed.

As Larry continues to move west-northwest, the ridge axis will gradually re-position to the northeast of the tropical cyclone, providing an avenue for the hurricane to begin gaining more latitude. Starting around 72 hours, a bit more cross-track spread begins to emerge in the track guidance, related to both how much ridging remains directly poleward of Larry, and also the outer-core size of the tropical cyclone itself. For example, the most recent GFS run shifts most of the ridging to the east of Larry and also expands the outer radius of cyclone dramatically, helping to widen the poleward weakness allowing a more northward track by 120 hours. By contrast, the ECMWF maintains a more compact hurricane in the mid-levels, and maintains more mid-level ridging to the north of the cyclone. These differences in the ECMWF allow a bit more of a westward track closer to the Island of Bermuda. For now, the latest NHC track forecast is in between these solutions, though with a slight preference towards the ECMWF, which is also close to the latest HCCA consensus aid forecast. This track forecast is quite similar to the previous forecast. Given the track uncertainty by day 5, it is too soon to determine what impacts Larry may pose to the Island of Bermuda, but interests there should monitor updates in the forecast in the subsequent days.

Larry remains embedded in a favorable environment for intensification, with low vertical wind shear under 10 kt and a sufficently moist mid-level environment. However, the hurricane has had difficulty closing off its inner-core structure, which might be preventing more rapid development from taking place. Assuming its inner core becomes better established, Larry is expected to intensity at a decent clip over the next 36-48 hours, and is forecast to become a major hurricane this weekend with a peak intensity of 120 kt by Monday. Afterwards, both the ECMWF-SHIPS guidance and latest HWRF run suggest that westerly vertical wind shear, from an upper-level mid-oceanic trough positioned northwest of Larry, could begin to undercut the favorable upper-level environment of the large tropical cyclone. Thus, some gradual weakening is shown from days 3-5 in the NHC intensity forecast. This latest forecast is quite similar to the previous one and is on the upper-end of the guidance envelope, though still not as high as the most recent COAMPS-TC and experimental HAFS-B runs. This intensity forecast also does not account for possible eyewall replacement cycles, which could cause additional intensity fluctuations that are difficult to predict several days in advance.

Significant ocean swells generated by the large wind field of Larry are expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and high surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well.

FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 14.8N  40.7W   80 KT  90 MPH - Category 1 (ESE Praia,Cape Verde)
 12H  04/0000Z 15.4N  42.8W   90 KT 105 MPH - Category 2 (ESE Praia,Cape Verde)
 24H  04/1200Z 16.5N  45.3W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  05/0000Z 17.6N  47.6W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  05/1200Z 19.0N  49.8W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  06/0000Z 20.2N  51.8W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  06/1200Z 21.4N  53.6W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  07/1200Z 24.2N  56.9W  115 KT 130 MPH - Category 3 (ESE St. George's,Bermuda)
120H  08/1200Z 27.8N  60.0W  105 KT 120 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Fri Sep 03, 2021 

Larry continues to gradually become better organized. Satellite images show a fairly compact central dense overcast feature with an eye occasionally evident. Beyond the inner core, banding features are gradually becoming more distinct, especially to the south of the center. The latest Dvorak classifications at 0600 UTC was 4.5/77 kt from TAFB and SAB, and based on those estimates and the improving trend, the initial intensity is nudged upward to 80 kt.

Larry is moving west-northwestward at 17 kt. There has been no change to the track forecast reasoning. A continued westward to west-northwestward motion is expected on Friday and through the weekend as the hurricane remains on the south side of a mid-level ridge. By early next week, Larry is expected to slow down and turn northwestward when it reaches the southwestern periphery of the ridge. The models are in fairly good agreement, and the NHC track forecast lies near the middle of the guidance envelope. This forecast is largely an update of the previous one.

The environmental factors appear favorable for steady strengthening during the next few days with wind shear remaining low and mid-level moisture fairly high. The only slightly negative factor is marginally warm 26-27 deg C waters that Larry will be moving over during the next couple of days, which should prevent rapid intensification. All of the models are in general agreement that Larry will become a major hurricane in a day or so with continued strengthening through day 3, and the NHC intensity forecast follows suit. Some weakening is shown by the end of the forecast period when the wind shear could increase a little. This forecast is very similar to the previous one and lies near the high end of the guidance envelope. It should be noted that eyewall replacement cycles are possible, which could cause intensity fluctuations that are challenging to predict.

The leading swell front from Larry is expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and high surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 14.6N  38.9W   80 KT  90 MPH - Category 1 (ESE Praia,Cape Verde)
 12H  03/1800Z 15.2N  41.1W   90 KT 105 MPH - Category 2 (ESE Praia,Cape Verde)
 24H  04/0600Z 16.2N  43.8W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 36H  04/1800Z 17.3N  46.2W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  05/0600Z 18.6N  48.5W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  05/1800Z 19.8N  50.5W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  06/0600Z 21.1N  52.5W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  07/0600Z 23.8N  55.8W  115 KT 130 MPH - Category 3 (ESE St. George's,Bermuda)
120H  08/0600Z 27.1N  58.9W  110 KT 125 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Thu Sep 02, 2021

A series of SSMIS microwave passes earlier this afternoon indicated that Larry may have been starting an eyewall replacement. However, the last pass at 2058 UTC suggested that the eyewall replacement failed, with the western part of the outer eyewall being eroded, possibly by some modest mid-level shear and some dry air, and the tighter inner eyewall trying to re-establish itself. As a result, the convective pattern has reverted back to a small Central Dense Overcast. Subjective Dvorak intensity estimates are now T4.5/77 kt from TAFB and T4.0/65 kt from SAB, and the latest objective estimates range from 72 to 78 kt. Overall these numbers have risen a bit, and Larry’s maximum winds are now estimated to be 75 kt.

Larry continues moving toward the west but perhaps slightly faster (280/17 kt). There is no change to the track forecast reasoning. A fairly stagnant pattern consisting of a strong mid-level high over the central Atlantic and broad-scale troughing over the eastern United States and western Atlantic should persist through the 5-day forecast period. Larry is therefore forecast to turn toward the west-northwest on Friday and then take on a northwest heading Sunday through Tuesday while it moves around the southwestern periphery of the high. The updated NHC track forecast lies right along the previous forecast and is very close to the various consensus aids.

Low shear, gradually increasing sea surface temperatures, and the potential for an upper-level outflow jet to form north of the hurricane during the next 24-48 hours should support continued strengthening. During the first 48 hours, the NHC forecast shows a steady increase of 10 kt every 24 hours, close to the HCCA consensus aids and near the top of the guidance envelope. By days 3 and 4, there continue to be indications that increasing westerly or northwesterly shear could become a factor, and the NHC forecast therefore shows a leveling off of the intensity, with some slight weakening by the end of the forecast period. If Larry becomes a strong hurricane, eyewall replacements would also be a possibility, which would likely lead to difficult-to-forecast fluctuations in intensity.

The leading swell front from Larry is expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 14.1N  37.5W   75 KT  85 MPH - Category 1 (ESE Praia,Cape Verde)
 12H  03/1200Z 14.5N  39.9W   85 KT 100 MPH - Category 2 (ESE Praia,Cape Verde)
 24H  04/0000Z 15.3N  42.6W   95 KT 110 MPH - Category 2 (ESE Praia,Cape Verde)
 36H  04/1200Z 16.4N  45.2W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 48H  05/0000Z 17.6N  47.5W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 60H  05/1200Z 19.0N  49.7W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  06/0000Z 20.4N  51.8W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  07/0000Z 22.9N  55.0W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
120H  08/0000Z 25.9N  58.0W  110 KT 125 MPH - Category 3 (ESE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Thu Sep 02, 2021 

Larry continues to gradually become better organized this morning, with a small but cold CDO near the estimated center, and well defined curved bands rotating completely around. Unfortunately, there have not been any recent microwave passes over the center in the last 6-9 hours. However, I did receive a helpful ASCAT-B pass at 1128 UTC which indicated that while the inner core remains quite small, the 34-kt wind radii have expanded dramatically in all quadrants. The most recent Dvorak subjective intensity estimates were both CI 4.0/65 kt from SAB and TAFB. However, the objective intensity estimates from SATCON and ADT are higher, at 70 kt and 77 kt respectively. Thus, the current intensity of Larry was nudged upward to 70 kt for this advisory. The hurricane’s heading has changed little this morning, estimated at 280/15 kt. There also remains little change to the forecast track reasoning. A dominant mid-level ridge is located north of Larry and should maintain the hurricane on a west to west-northwest heading over the next 72 hours.

The track guidance is in excellent agreement over this time period. After 72 hours, a bit more track guidance spread begins to take shape, which appears related to the evolution of the the steering ridge orientation. For example, the most recent GFS run begins a more pronounced rightward bend, as the ridge becomes positioned northeast of the tropical cyclone. In contrast, the ECMWF and a number of its left-leaning ensemble members maintain more ridging directly north of Larry, keeping the hurricane on a more leftward track with only a gradual bend to the west-northwest and northwest. These differences notwithstanding, the consensus aids has changed little from the previous forecast cycle, and the NHC forecast track is nearly identical to the previous track. This track lies very close to the HCCA consensus aid, which favors a track solution a bit closer to the ECMWF versus the GFS.

Larry’s environmental conditions appear very favorable for additional intensification over the next 60-72 hours. In fact, the primarily forecast challenge relates to how Larry’s core structure evolves over the next several days. Right now, the inner-core and hurricane-force wind radii are very small relative to the expanding tropical-storm-force wind field around the storm. Thus, it appears likely that Larry will undergo some form of an eyewall replacement cycle (ERC) in the next 12 to 24 hours, which may slow down the short term intensification rate. However, once this cycle is complete, very light easterly vertical wind shear between 2-8 kt, abundant mid-level moisture, and sufficently warm sea-surface temperatures between 27-28 C should favor steady to rapid intensification.

The latest NHC intensity forecast now calls for a peak intensity of 120 kt in roughly 72 hours, which is a faster and slightly higher peak than the prior forecast. Afterwards, the guidance is a bit conflicted. The GFS-based SHIPS continues to suggests low vertical wind shear through the end of the forecast period. However, the ECMWF-based SHIPS shows much higher southwesterly vertical wind shear beginning in 84 hours as Larry also moves into a drier environment. It is also possible additional ERCs may occur in the latter portion of this forecast, resulting in additional intensity fluctuations. For these reasons, the intensity forecast at the end of the period shows some modest weakening. This intensity forecast is a bit higher than the HCCA corrected consensus aid, but remains lower than some of the more aggressive guidance (COAMPS-TC, the experimental HAFS-B).

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 13.5N  34.2W   70 KT  80 MPH - Category 1 (ESE Praia,Cape Verde)
 12H  03/0000Z 13.8N  36.7W   75 KT  85 MPH - Category 1 (ESE Praia,Cape Verde)
 24H  03/1200Z 14.4N  39.7W   85 KT 100 MPH - Category 2 (ESE Praia,Cape Verde)
 36H  04/0000Z 15.3N  42.6W   95 KT 110 MPH - Category 2 (ESE Praia,Cape Verde)
 48H  04/1200Z 16.5N  45.2W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  05/0000Z 17.9N  47.6W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
 72H  05/1200Z 19.2N  49.7W  120 KT 140 MPH - Category 4 (ENE Codrington,Barbuda)
 96H  06/1200Z 21.8N  53.1W  115 KT 130 MPH - Category 4 (ENE Codrington,Barbuda)
120H  07/1200Z 24.6N  56.0W  110 KT 125 MPH - Category 3 (ENE Codrington,Barbuda)

NWS National Hurricane Center Miami FL 800 PM CVT Wed Sep 01, 2021 

Afternoon satellite imagery indicates that Larry continues to become better organized, with visible imagery hinting at eye formation and a partial SSM/IS overpass suggesting that a 37 GHz convective ring is present around the center. Satellite intensity estimates are now 65 kt from SAB and 55 kt from TAFB, and the initial intensity is increased to 60 kt, which is a 30 kt increase since this time yesterday satisfying the 24-h definition of rapid intensification.

The initial motion is now 275/19 kt. Larry is expected to move around the south and southwest sides of a subtropical ridge during the next five days, with a general westward motion for 24-36 h, followed by a turn toward the west-northwest and, by 96-120 h, a turn toward the northwest. The spread in the track guidance after 36 h has decreased a little in the latest model runs. However, the guidance envelope has again shifted a little to the west. The new forecast track will also be shifted a little westward, and it lies on the southern edge of the various consensus models.

Conditions appear favorable for additional rapid intensification during at the next 36-48 h, and the intensity forecast now calls for Larry to become a hurricane in less than 12 h and become a major hurricane in about 48 h. Given current trends, this part of the intensity forecast could be conservative. There is lower confidence in the intensity forecast after 48 h. Larry is expected to encounter somewhat increased shear, and around the 72 h point it is expected to encounter some dry air. After 96 h, moderate shear is forecast to continue, but the cyclone is expected to move into a more moist air mass and over increasing sea surface temperatures. On top of these factors, there is the good chance that Larry will have fluctuations in intensity after it becomes a major hurricane due to eyewall replacement cycles. The intensity guidance basically keeps a steady intensity from 60-120 h, and the official forecast follows that trend. However, this part of the intensity forecast is in the middle of the guidance, and it is possible Larry could be stronger than forecast during this time.

FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 12.5N  29.4W   60 KT  70 MPH - Tropical Storm (ESE Praia,Cape Verde)
 12H  02/0600Z 12.6N  31.8W   70 KT  80 MPH - Category 1 (ESE Praia,Cape Verde)
 24H  02/1800Z 13.0N  34.9W   85 KT 100 MPH - Category 2 (ESE Praia,Cape Verde)
 36H  03/0600Z 13.7N  38.0W   95 KT 110 MPH - Category 2 (ESE Praia,Cape Verde)
 48H  03/1800Z 14.6N  40.9W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 60H  04/0600Z 15.6N  43.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 72H  04/1800Z 16.9N  46.2W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 96H  05/1800Z 19.5N  50.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
120H  06/1800Z 22.5N  54.0W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)

NWS National Hurricane Center Miami FL 200 PM CVT Wed Sep 01, 2021

Satellite imagery this morning shows that Larry is becoming better organized, with curved convective bands increasing around the center. Various subjective and objective satellite intensity estimates were in the 35-55 kt range around 12Z, and ASCAT data near the time showed 40 kt winds. Based on increasing organization since that time, the initial intensity is increased to 45 kt.

Larry is moving quickly westward, although there is some uncertainty in the forward speed due to the possibility the center re-formed during the night. The best estimate of the motion is 270/19 kt. As noted in the previous advisory, the cyclone is expected to move around the southern and southwestern periphery of the sprawling Bermuda-Azores ridge for the next 5 days, resulting in a general west motion for 24-36 h, followed by a turn toward the west-northwest and, by 96-120 h, a turn toward the northwest. After 36 h, there is some spread in the track guidance, with the GFS generally on the right side of the guidance envelope and the UKMET on the left side, a spread often seen for westward-moving cyclones south of the Bermuda-Azores high. Due to a more westerly initial position, the guidance has shifted a little more to the west, and the new forecast track is again shifted to the west of the previous track. The new forecast lies a little to the south of the various consensus models.

Conditions appear favorable for steady to rapid strengthening during the next 48-60 h due to light shear, a moist environment, and sea surface temperatures of 27-28C along the forecast track. The new intensity forecast calls for Larry to become a hurricane in about 24 h and a major hurricane near 60 h. After that time, the global models suggest the possibility of dry air entrainment, and by 120 h there is likely to be moderate westerly shear over the cyclone. Based on this forecast environment and the guidance trends, the intensity forecast calls for little change in strength from 72-120 h. The new intensity forecast lies near the upper edge of the intensity guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 12.3N  27.6W   45 KT  50 MPH - Tropical Storm (ESE Praia,Cape Verde)
 12H  02/0000Z 12.4N  30.4W   55 KT  65 MPH - Tropical Storm (ESE Praia,Cape Verde)
 24H  02/1200Z 12.7N  33.4W   65 KT  75 MPH - Category 1 (ESE Praia,Cape Verde)
 36H  03/0000Z 13.2N  36.5W   75 KT  85 MPH - Category 1 (ESE Praia,Cape Verde)
 48H  03/1200Z 13.9N  39.2W   90 KT 105 MPH - Category 2 (ESE Praia,Cape Verde)
 60H  04/0000Z 15.0N  41.9W  100 KT 115 MPH - Category 3 (ENE Codrington,Barbuda)
 72H  04/1200Z 16.2N  44.6W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
 96H  05/1200Z 19.0N  49.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)
120H  06/1200Z 22.0N  52.5W  105 KT 120 MPH - Category 3 (ENE Codrington,Barbuda)

NWS National Hurricane Center Miami FL 200 AM CVT Wed Sep 01, 2021  

Satellite images indicate that the depression is gradually becoming better organized. An area of deep convection has been persisting near the center, and banding features are beginning to take shape. The latest Dvorak estimates from TAFB and SAB have increased to 2.5/35 kt, which would support upgrading the system to a tropical storm. However, a recent ASCAT-B overpass around 2300 UTC showed maximum winds in the 25-30 kt range in the northeastern quadrant, and based on that data the initial intensity is held at 30 kt.

The tropical depression is moving fairly quickly to the west-northwest at 17 kt. The track forecast reasoning appears fairly straightforward. The cyclone is expected to move at a relatively fast pace to the west or west-northwest during the next couple of days as it remains on the south side of a strong mid-level ridge. After that time, a decrease in forward speed and a gradual turn to the northwest are expected as the system nears the southwestern side of the ridge. Although most of the models agree on the synoptic steering pattern, there is a fair amount of spread from days 3 to 5 in how soon the northwestward turn will occur. The NHC track forecast lies near the middle of the guidance envelope and is a little to the north of the previous one based on the more poleward initial position.

Since the system is expected to be over relatively warm water and in an air mass of low wind shear and abundant moisture, steady strengthening is expected during the next couple of days. The depression is likely to become a tropical storm within the next 12 hours and a hurricane in 36 to 48 hours. Beyond a few days, an increase in shear and drier air should slow the rate of intensification. The NHC intensity forecast follows the trend of the HCCA, IVCN, and IVDR models. In addition, the global models all show the cyclone becoming fairly large toward the end of the forecast period. The NHC forecast wind radii is larger than the previous one, trending toward the radii consensus aid.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 12.1N  23.2W   30 KT  35 MPH - Depression (ESE Praia,Cape Verde)
 12H  01/1200Z 12.6N  25.9W   40 KT  45 MPH - Tropical Storm (ESE Praia,Cape Verde)
 24H  02/0000Z 12.8N  29.2W   50 KT  60 MPH - Tropical Storm (ESE Praia,Cape Verde)
 36H  02/1200Z 13.2N  32.1W   60 KT  70 MPH - Tropical Storm (ESE Praia,Cape Verde)
 48H  03/0000Z 13.8N  35.1W   70 KT  80 MPH - Category 1 (ESE Praia,Cape Verde)
 60H  03/1200Z 14.5N  37.5W   80 KT  90 MPH - Category 1 (ENE Codrington,Barbuda)
 72H  04/0000Z 15.4N  40.1W   85 KT 100 MPH - Category 2 (ENE Codrington,Barbuda)
 96H  05/0000Z 18.0N  44.5W   90 KT 105 MPH - Category 2 (ENE Codrington,Barbuda)
120H  06/0000Z 20.7N  47.9W   95 KT 110 MPH - Category 2 (ENE Codrington,Barbuda)

NWS National Hurricane Center Miami FL 800 AM EDT Tue Aug 31, 2021

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

The National Hurricane Center is issuing advisories on Tropical Storm Kate, located over the central tropical Atlantic. The Weather Prediction Center is issuing Public Advisories on Tropical Depression Ida, located over northeastern Mississippi.

  • 1. A well-defined low pressure system is located over the far eastern tropical Atlantic, a couple of hundred miles west-southwest of the coast of Guinea. Associated showers and thunderstorms continue to show signs of organization, and environmental conditions are conducive for additional development of this system. A tropical depression is likely to form during the next day or so while the low moves westward to west-northwestward at 10 to 15 mph. * Formation chance through 48 hours…high..90 percent. * Formation chance through 5 days…high...90 percent.
  • 2. A broad area of low pressure is forecast to develop over the southwestern Caribbean Sea during the next couple of days. Some slow development of this system is possible by the end of the week, if the system remains over water. This system is expected to move gradually west-northwestward or northwestward at 5 to 10 mph toward Central America. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Mon Aug 30 2021

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

The National Hurricane Center is issuing advisories on Tropical Storm Ida, located inland over western Mississippi, and on recently upgraded Tropical Storm Kate, located over the central tropical Atlantic.

  • 1. Satellite-derived wind data and satellite imagery indicate that an area of low pressure has formed over the far eastern Tropical Atlantic in association with a tropical wave that recently moved off the west coast of Africa. Environmental conditions are conducive for development, and a tropical depression is likely to form within the next couple of days while the system moves west-northwestward at 10 to 15 mph over the eastern tropical Atlantic. * Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high…90 percent.
  • 2. A broad area of low pressure is expected to form in the southern Caribbean Sea by midweek. Environmental conditions appear to be favorable for some slow development by the end of the week, as long as the system remains over water. This system is expected to move gradually west-northwestward or northwestward at 5 to 10 mph over the western Caribbean Sea near the east coast of Central America. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...20 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Mon Aug 30 2021

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

The National Hurricane Center is issuing advisories on Tropical Storm Ida, located inland over southwestern Mississippi, and on Tropical Depression Ten, located over the central tropical Atlantic.

  • 1. A tropical wave near the west coast of Africa is expected to move over the eastern Tropical Atlantic later today. Environmental conditions appear conducive for the development of a low pressure area once the wave moves offshore, and a tropical depression is likely to form by the middle or latter part of the week while the system moves west-northwestward at 10 to 15 mph over the eastern tropical Atlantic. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…high…80 percent.
  • 2. A broad area of low pressure is expected to form in the southern Caribbean Sea over the next several days. Environmental conditions appear to be favorable for some slow development by the end of the week, as long as the system remains over water. This system is expected to move gradually west-northwestward or northwestward at 5 to 10 mph over the western Caribbean Sea close to the east coast of Central America. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...20 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Sun Aug 29, 2021

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

The National Hurricane Center is issuing advisories on Hurricane Ida, located inland over southeastern Louisiana, on Tropical Depression Ten, located over the central tropical Atlantic, and on Tropical Storm Julian, located over the central subtropical Atlantic.

  • 1. A broad area of low pressure located just east of the Delmarva Peninsula is producing a few disorganized showers and thunderstorms. Upper-level winds are expected to increase over the low on Monday and Tuesday, and any development of this system is expected to be slow to occur while it moves slowly southeastward and then eastward, away from the east coast of the United States. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…10 percent.
  • 2. A tropical wave is expected to emerge off the west coast of Africa by Monday night. Environmental conditions appear conducive for the development of a low pressure area once the wave moves offshore, and a tropical depression is likely to form by the middle or latter part of the week while the system moves west-northwestward at 10 to 15 mph over the eastern tropical Atlantic. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...80 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Sun Aug 29, 2021

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

The National Hurricane Center is issuing advisories on Hurricane Ida, which has made landfall on the coast of southeastern Louisiana, on Tropical Depression Ten, located over the central tropical Atlantic, and on recently upgraded Tropical Storm Julian, located over the central subtropical Atlantic.

  • 1. A broad area of low pressure located just east of the Delmarva Peninsula is producing a few disorganized showers and thunderstorms. Upper-level winds are expected to increase over the low on Monday and Tuesday, and any development of this system is expected to be slow to occur while it moves slowly southeastward and then eastward, away from the east coast of the United States. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low...10 percent.
  • 2. A tropical wave is expected to emerge off the west coast of Africa by Monday night. Environmental conditions appear conducive for the development of a low pressure area once the wave moves offshore, and a tropical depression is likely to form by the middle or latter part of the week while the system moves west-northwestward at 10 to 15 mph over the eastern tropical Atlantic. * Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Sat Aug 28, 2021

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

The National Hurricane Center is issuing advisories on Hurricane Ida, located over the east-central Gulf of Mexico, and on Tropical Depression Ten, located over the central tropical Atlantic.

  • 1. Showers and thunderstorms continue to show signs of organization in association with an area of low pressure located over the central Atlantic. Although environmental conditions remain only marginally conducive for further development, only a slight increase in organization would result in the formation of a tropical depression later tonight or on Sunday. In a couple of days, the system is forecast to be absorbed by a frontal system. The disturbance is expected to drift eastward through tonight, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent.
  • 2. A tropical wave is expected to emerge off the coast of west Africa by the middle of next week. Thereafter, environmental conditions appear conducive for gradual development, and a tropical depression is likely to form toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…high…70 percent.

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