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| #1158420 (Received by flhurricane at: 10:38 AM 22.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 17 NWS National Hurricane Center Miami FL AL202023 1100 AM AST Sun Oct 22 2023 Tammy is slowly pulling away from the northern Leeward Islands and all of the hurricane warnings were dropped at the 1200 UTC intermediate advisory. However, there is still a trailing area of showers and thunderstorms that will likely cause heavy rain across portions of the Windward and Leeward Islands throughout the day. The hurricane is exhibiting a central dense overcast pattern in satellite images with very cold cloud tops persisting near the center. Both the NOAA and Air Force Hurricane Hunters are investigating Tammy, and based on the data they have collected, the initial intensity is nudged downward slightly to 70 kt. Tammy remains a fairly compact and asymmetric tropical cyclone with hurricane-force and tropical-storm-force winds only extending up to 20 n mi and 120 n mi from the center, respectively. The wind radii are particularly small on the southwest side of the system. The hurricane is moving northwestward at 8 kt on the southwestern periphery of a subtropical ridge centered over the central Atlantic. A turn to the north is forecast to occur tonight, followed by a northeastward motion on Tuesday and Wednesday when a large-scale trough over the northeast U.S. shifts eastward, eroding the ridge. After that time, the models show the trough cutting off and merging with Tammy, which could cause a turn to the left. Although the models are in better agreement than they were yesterday, there is still a considerable amount of spread at long range due to differences in the synoptic pattern and model predicted intensity of Tammy. Only small changes were made to the previous NHC track forecast, and it continues to lie close to the HCCA guidance. The environmental factors for Tammy appear to be mixed. The system is expected to remain over warm SSTs during at least the next few days, but it will also be in an environment of moderate vertical wind shear. Therefore, fluctuations in strength seem likely over the next few days. After Tammy merges with the trough, dry air entrainment and stronger shear should cause some weakening and likely lead to extratropical transition in 4 to 5 days. The NHC intensity forecast is a little lower than the previous one, and near the middle of the guidance envelope. KEY MESSAGES: 1. The heaviest rains from Tammy will continue over the Leeward Islands through tonight. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 19.1N 63.0W 70 KT 80 MPH 12H 23/0000Z 20.1N 63.6W 70 KT 80 MPH 24H 23/1200Z 21.4N 63.9W 75 KT 85 MPH 36H 24/0000Z 22.3N 63.5W 75 KT 85 MPH 48H 24/1200Z 23.0N 62.9W 75 KT 85 MPH 60H 25/0000Z 23.6N 62.0W 75 KT 85 MPH 72H 25/1200Z 24.5N 61.0W 75 KT 85 MPH 96H 26/1200Z 27.5N 60.5W 65 KT 75 MPH 120H 27/1200Z 30.0N 63.9W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi |
