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| #1158783 (Received by flhurricane at: 10:47 PM 24.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 27 NWS National Hurricane Center Miami FL AL202023 1100 PM AST Tue Oct 24 2023 Satellite data indicate Tammy has strengthened tonight. Deep convection has increased near and over the center of the hurricane during the past several hours, resulting in a cold and expanding central dense overcast with intermittent glimpses of a ragged eye. Recent SSMIS and GMI passive microwave images show a tighter inner core compared to earlier today, with a mid-level eyewall that mostly wraps around the center. The subjective Dvorak estimates from SAB and TAFB have risen to T4.5/77 kt and T4.0/65 kt, respectively, with similar increases in the various UW-CIMSS objective estimates. Thus, the initial intensity is raised to 75 kt for this advisory. Despite strengthening upper-level winds over Tammy, increasing upper-level divergence associated with a deep-layer trough over the western Atlantic could support some additional intensification in the near term, as shown by the GFS and some of the regional models. Given recent trends, the updated NHC intensity forecast is raised at 12-24 h to account for this potential. Then, Tammy is expected to merge with a cold front currently analyzed to the northwest of the hurricane. This extratropical transition is forecast to be completed by 36 h, with an expansion of Tammy`s wind field as it becomes a hurricane-force extratropical cyclone. Thereafter, the global models show the frontal cyclone weakening through the rest of the period. There is some potential it could shed its frontal structure this weekend, but for now the model-simulated satellite imagery does not show much increase in convection during that time. Tammy is moving northeastward (50 degrees/8 kt) within the flow between a deep-layer trough over the western Atlantic and a subtropical ridge over the central Atlantic. Tammy is expected to turn northward during the next day or so as it becomes captured by the upper trough. The updated NHC forecast lies slightly right of the previous one in the first 24 h, mostly based on the more northeastward initial position. Then, the cyclone is forecast to move more slowly northwestward in 2-3 days within weaker steering currents. The long-range track forecast is highly uncertain, with diverging global and ensemble model solutions that move the shallower cyclone in opposite directions. Given the above-average uncertainty, it seems prudent to make little change to this portion of the track forecast at this time. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 24.9N 60.7W 75 KT 85 MPH 12H 25/1200Z 26.1N 59.9W 85 KT 100 MPH 24H 26/0000Z 28.1N 59.1W 80 KT 90 MPH 36H 26/1200Z 29.6N 59.7W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 27/0000Z 30.5N 60.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 60H 27/1200Z 30.9N 61.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 28/0000Z 31.3N 62.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 29/0000Z 31.4N 63.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 30/0000Z 31.0N 64.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Reinhart |
