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| #1157966 (Received by flhurricane at: 5:05 AM 19.Oct.2023) TCDAT5 Tropical Storm Tammy Discussion Number 3 NWS National Hurricane Center Miami FL AL202023 500 AM AST Thu Oct 19 2023 Tammy has not changed much overnight. Satellite images show a persistent area of deep convection, but the pattern remains ragged with little evidence of banding features. The low-level center has occasionally been exposed near the western edge of the convection due to westerly vertical wind shear. The initial intensity is held at 35 kt, in agreement with the Dvorak classification from TAFB. The NOAA Hurricane Hunters will be investigating the storm later this morning, and the data they collect will provide a better assessment of Tammy`s intensity, center position, and overall structure. The storm is moving generally westward at about 15 kt. Tammy is expected to turn west-northwestward later today and likely northwestward on Friday as it moves along the southwestern periphery of a subtropical ridge over the central Atlantic. This should take Tammy near or over the Leeward Islands Friday and Friday night. After that time, a gradual turn to the north and then the northeast is predicted as Tammy moves in the flow between the ridge and an approaching mid- to upper-level trough over the western Atlantic. The NHC track forecast is similar to the previous one in the short term, but is slower at days 4 and 5 based on the new model guidance. The GFS and ECMWF models have come into better agreement this cycle, and both lie a little to the right of the NHC forecast during from 12 to 72 hours. Tammy will be moving over very warm 30 C SSTs as it nears the Leeward Islands, which should allow the storm to strengthen despite continued moderate wind shear. The storm will likely be near hurricane strength when it moves near the Leeward Islands. Additional strengthening is expected when the system recurves over the central Atlantic while it remains over warm water and also gains baroclinic support from the aforementioned trough. The NHC intensity forecast is largely an update of the previous one and is in line with the HCCA and IVCN consensus guidance. KEY MESSAGES: 1. Tropical storm conditions are possible across portions of the Lesser Antilles beginning on Friday, where tropical storm watches are currently in effect. Additional watches and warnings will likely be required later today. 2. Heavy rains from Tammy will begin to affect the northern Windward and Leeward Islands on Friday, spreading into the British and U.S. Virgin Islands and Puerto Rico over the weekend. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 13.5N 54.8W 35 KT 40 MPH 12H 19/1800Z 13.9N 56.4W 40 KT 45 MPH 24H 20/0600Z 14.5N 58.2W 50 KT 60 MPH 36H 20/1800Z 15.5N 60.0W 50 KT 60 MPH 48H 21/0600Z 16.8N 61.3W 55 KT 65 MPH 60H 21/1800Z 18.4N 62.4W 55 KT 65 MPH 72H 22/0600Z 19.9N 63.1W 60 KT 70 MPH 96H 23/0600Z 23.3N 63.0W 70 KT 80 MPH 120H 24/0600Z 27.2N 59.5W 70 KT 80 MPH $$ Forecaster Cangialosi |
