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| #1158557 (Received by flhurricane at: 11:01 AM 23.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 21 NWS National Hurricane Center Miami FL AL202023 1100 AM AST Mon Oct 23 2023 Tammy appears to be holding steady in spite of the moderate southwesterly vertical wind shear. There have been regular bursts of deep convection over the center and a fragmented band around the eastern portion of the circulation. The latest intensity is held at 70 kt to represent a blend of the subjective satellite intensity estimates from TAFB and SAB, which were 77 kt and 65 kt, respectively. The hurricane is moving northward at 005/6 kt. Tammy should continue to turn north-northeastward to northeastward in the flow between a mid-latitude trough over the western Atlantic and a mid-level ridge over the central subtropical Atlantic. Beyond 60 h, there is still a significant spread in the model guidance. Most of the regional models and the GFS model forecast Tammy to continue northward around the western side of the ridge. A different cluster of model solutions, including the ECMWF, merge Tammy with a cutoff low that forms from the trough and turns the cyclone northwestward to westward. The latest NHC track forecast favors the latter scenario and has been nudged slightly north of the previous prediction. Southwesterly shear appears to be influencing Tammy`s structure. The vertical wind shear is expected to persist and likely increase in about 36 h, forcing some dry mid-level air into the cyclone`s circulation. These environmental conditions should lead to gradual weakening. Model guidance predicts that Tammy should undergo structural changes over the next couple of days as it interacts with the aforementioned cutoff low. The latest official intensity forecast now shows Tammy becoming extratropical in 72 hours. KEY MESSAGES: 1. Heavy rain from Tammy will remain possible over the British Virgin Islands and Leeward Islands through today. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 21.9N 63.9W 70 KT 80 MPH 12H 24/0000Z 22.7N 63.4W 70 KT 80 MPH 24H 24/1200Z 23.6N 62.4W 75 KT 85 MPH 36H 25/0000Z 24.5N 61.2W 80 KT 90 MPH 48H 25/1200Z 25.8N 59.9W 75 KT 85 MPH 60H 26/0000Z 27.3N 58.9W 70 KT 80 MPH 72H 26/1200Z 29.1N 58.6W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 27/1200Z 31.2N 60.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 28/1200Z 32.4N 63.6W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Bucci |
