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| #1158460 (Received by flhurricane at: 4:47 PM 22.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 18 NWS National Hurricane Center Miami FL AL202023 500 PM AST Sun Oct 22 2023 The core of Tammy continues to pull away from the northern Leeward Islands, but a trailing area of heavy rain continues to affect portions of the Windward and Leeward Islands. The NOAA Hurricane Hunters found maximum 750-mb flight-level winds of 83 kt and peak SFMR winds of around 70 kt. In addition, the minimum pressure has fallen to 988 mb. These data support nudging the initial intensity up to 75 kt. Tammy continues to have a small central dense overcast pattern in satellite images with very cold cloud tops evident near the center. An ASCAT-B pass from a few hours ago was helpful in adjusting the 34- and 50-kt wind radii, and it confirmed that Tammy remains a relatively compact tropical cyclone. 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 late tonight, followed by a northeastward motion beginning Monday night 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 will likely cause a sharp turn to the left. The models have come in slightly better agreement in the overall scenario, and only small changes were made to the previous NHC track forecast. Tammy will likely fluctuate in strength during the next few days while it remains over warm SSTs and in a moderate wind shear environment. After Tammy merges with the trough, dry air entrainment and stronger shear should cause weakening and likely lead to extratropical transition in 3 to 4 days. The NHC intensity forecast is similar to the previous one and roughly in 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 22/2100Z 19.9N 63.4W 75 KT 85 MPH 12H 23/0600Z 20.9N 63.8W 75 KT 85 MPH 24H 23/1800Z 22.0N 63.6W 80 KT 90 MPH 36H 24/0600Z 22.8N 62.9W 80 KT 90 MPH 48H 24/1800Z 23.6N 62.0W 80 KT 90 MPH 60H 25/0600Z 24.4N 61.0W 80 KT 90 MPH 72H 25/1800Z 25.8N 60.2W 75 KT 85 MPH 96H 26/1800Z 28.9N 60.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 27/1800Z 30.7N 64.3W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi |
