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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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