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Hurricane Larry Forecast Discussion Number 25
2021-09-06 22:45:42| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Sep 06 2021 000 WTNT42 KNHC 062045 TCDAT2 Hurricane Larry Discussion Number 25 NWS National Hurricane Center Miami FL AL122021 500 PM AST Mon Sep 06 2021 NOAA aircraft have been investigating Larry for much of this afternoon, providing valuable information regarding the structure and intensity of the hurricane. Peak 700-mb flight-level winds of 110 kt with SFMR winds of 101 kt were measured in the northwestern eyewall a couple of hours ago, supporting an intensity of about 100 kt in that portion of the cyclone. During that pass through the hurricane, the aircraft tail Doppler radar measured winds of 121 kt at a height of 3 km in the northeastern eyewall, which equate to about 109 kt at the surface. Therefore, the initial intensity has been adjusted up to 110 kt for this advisory. A pair of dropsondes into the eye of Larry measured a minimum central pressure of 956 mb. Both the aircraft and earlier ASCAT data indicated that hurricane-force winds extend up to 60 n mi from the center, while tropical-storm-force winds extend up to 160 n mi from the center. Larry is maintaining its stable, annular structure with a very large, mostly clear eye. The environment surrounding Larry is not forecast to change much over the next couple of days, so only some minor fluctuations in intensity are anticipated during that time. By 72 hours, decreasing sea-surface temperatures and an increase in vertical wind shear should cause the hurricane to begin weakening. The only change to the NHC intensity forecast was a 5-kt increase through the first few days to accommodate the adjustment required to the initial intensity. By the end of the forecast period, Larry is expected to transition to a powerful extratropical cyclone. The latest NHC forecast remains on the high end of the guidance, closest to the Decay-SHIPS model. The hurricane continues to move northwest at 9 kt to the southwest of a subtropical ridge. The forecast track confidence has remained high over the past few days. Larry should continue its northwestward motion through Wednesday, and then reach the western periphery of the ridge in a few days, causing the cyclone to begin a turn to the north, then northeast late this week. This track would bring Larry on its closest approach to Bermuda on Thursday. After turning northeast, the cyclone should accelerate into the mid-latitude westerlies. The latest NHC forecast is little changed from the previous one, and remains near the middle of tightly clustered track guidance. 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 06/2100Z 22.5N 53.9W 110 KT 125 MPH 12H 07/0600Z 23.4N 55.0W 110 KT 125 MPH 24H 07/1800Z 24.9N 56.3W 105 KT 120 MPH 36H 08/0600Z 26.5N 57.6W 105 KT 120 MPH 48H 08/1800Z 28.3N 59.1W 105 KT 120 MPH 60H 09/0600Z 30.4N 60.7W 105 KT 120 MPH 72H 09/1800Z 33.1N 61.7W 100 KT 115 MPH 96H 10/1800Z 41.2N 57.9W 90 KT 105 MPH 120H 11/1800Z 51.7N 46.4W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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Hurricane Larry Forecast Discussion Number 24
2021-09-06 16:56:02| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Sep 06 2021 000 WTNT42 KNHC 061455 TCDAT2 Hurricane Larry Discussion Number 24 NWS National Hurricane Center Miami FL AL122021 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 12H 07/0000Z 23.1N 54.0W 110 KT 125 MPH 24H 07/1200Z 24.5N 55.3W 110 KT 125 MPH 36H 08/0000Z 25.9N 56.6W 105 KT 120 MPH 48H 08/1200Z 27.5N 58.0W 100 KT 115 MPH 60H 09/0000Z 29.3N 59.6W 100 KT 115 MPH 72H 09/1200Z 31.6N 61.2W 95 KT 110 MPH 96H 10/1200Z 38.6N 60.0W 85 KT 100 MPH 120H 11/1200Z 49.0N 49.0W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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Hurricane Larry Forecast Discussion Number 23
2021-09-06 10:52:55| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Sep 06 2021 000 WTNT42 KNHC 060852 TCDAT2 Hurricane Larry Discussion Number 23 NWS National Hurricane Center Miami FL AL122021 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 12H 06/1800Z 22.6N 53.6W 110 KT 125 MPH 24H 07/0600Z 23.9N 54.9W 110 KT 125 MPH 36H 07/1800Z 25.3N 56.2W 105 KT 120 MPH 48H 08/0600Z 26.8N 57.5W 100 KT 115 MPH 60H 08/1800Z 28.5N 59.0W 100 KT 115 MPH 72H 09/0600Z 30.6N 60.6W 95 KT 110 MPH 96H 10/0600Z 36.7N 61.0W 90 KT 105 MPH 120H 11/0600Z 45.5N 52.0W 75 KT 85 MPH $$ Forecaster Reinhart
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Hurricane Larry Forecast Discussion Number 22
2021-09-06 04:52:52| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 05 2021 000 WTNT42 KNHC 060252 TCDAT2 Hurricane Larry Discussion Number 22 NWS National Hurricane Center Miami FL AL122021 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 12H 06/1200Z 22.0N 52.6W 110 KT 125 MPH 24H 07/0000Z 23.2N 54.1W 110 KT 125 MPH 36H 07/1200Z 24.6N 55.4W 105 KT 120 MPH 48H 08/0000Z 26.0N 56.7W 100 KT 115 MPH 60H 08/1200Z 27.6N 58.2W 95 KT 110 MPH 72H 09/0000Z 29.4N 59.9W 90 KT 105 MPH 96H 10/0000Z 34.4N 61.6W 85 KT 100 MPH 120H 11/0000Z 42.9N 55.8W 80 KT 90 MPH $$ Forecaster Papin
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Hurricane Larry Forecast Discussion Number 21
2021-09-05 22:54:05| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 05 2021 000 WTNT42 KNHC 052054 TCDAT2 Hurricane Larry Discussion Number 21 NWS National Hurricane Center Miami FL AL122021 500 PM AST Sun Sep 05 2021 The overall structure of Larry has changed little today. A large eye remains surrounded by a cold ring of convection with cloud tops of -75 to -80 C. The only notable difference between now and several hours ago has been that some cloud cover has become evident within the eye. A blend of the latest T- and CI-numbers from TAFB and SAB suggest that the initial intensity remains 110 kt. Larry is moving northwestward, or 315/11 kt, around the southwestern periphery of a subtropical ridge. There has been no change to the forecast track reasoning, nor has there been any notable change to the NHC forecast track from the previous advisory, due to the forecast models remaining in excellent agreement. A northwestward motion is expected to continue for the next few days to the southwest of the ridge. In a few days, the hurricane is forecast to reach the western periphery of this ridge, resulting in the cyclone beginning gradual recurvature to the north then northeast into the mid-latitude westerlies. Other than some minor fluctuations in intensity due to internal influences, the stable, annular-like structure of Larry should allow for it to remain a major hurricane for the next couple of days, despite being surrounded by some mid-level dry air. By day 4, the cyclone is forecast to move over waters of progressively decreasing oceanic heat content, which should induce gradual weakening. The latest NHC intensity forecast is little changed from the previous one, and is near the corrected consensus HCCA and DSHP, which have been two of the best performing models for Larry's intensity thus far. 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 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, 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 05/2100Z 20.5N 50.6W 110 KT 125 MPH 12H 06/0600Z 21.6N 51.9W 110 KT 125 MPH 24H 06/1800Z 22.7N 53.4W 110 KT 125 MPH 36H 07/0600Z 23.9N 54.8W 105 KT 120 MPH 48H 07/1800Z 25.3N 56.2W 100 KT 115 MPH 60H 08/0600Z 26.8N 57.5W 100 KT 115 MPH 72H 08/1800Z 28.5N 59.1W 100 KT 115 MPH 96H 09/1800Z 32.8N 61.3W 95 KT 110 MPH 120H 10/1800Z 39.8N 58.7W 85 KT 100 MPH $$ Forecaster Latto
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