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| #1019805 (Received by flhurricane at: 12:33 AM 04.Oct.2020) TCDAT5 Tropical Storm Gamma Discussion Number 7 NWS National Hurricane Center Miami FL AL252020 1000 PM CDT Sat Oct 03 2020 Tropical Storm Gamma remains over the northern portion of the Yucatan Peninsula, and the cyclone has been inland for about 10 hours now. Although the storm has weakened some, satellite images show that Gamma still has an intact central dense overcast feature and spiral bands on the north side of the circulation. The initial intensity is estimated to be 50 kt, but there is quite of bit of uncertainty in this value. The tropical storm is drenching the northern portion of the Yucatan Peninsula, and heavy rainfall is likely to continue there into Sunday. The tropical storm is moving northwestward at 6 kt on the southwestern periphery of an Atlantic subtropical ridge. Gamma is expected to move very slowly to the northwest or north-northwest toward a weakness in the ridge during the next 12 to 24 hours, and that should take the core of the tropical storm over the extreme southern Gulf of Mexico by early Sunday. By Sunday night and Monday, a combination of a building low- to mid-level ridge over the Gulf of Mexico and a developing low pressure area over the northwestern Caribbean Sea should cause Gamma to turn fairly sharply to the west or southwest early next week. A slow southwest or west motion is likely to continue into the middle of next week, and some of the models suggest that Gamma could become nearly stationary by the end of the forecast period. The NHC track forecast is largely an update of the previous one and lies near the TVCA and HCCA consensus models. The intensity forecast seems tricky. The tropical storm still appears well organized despite its time over land and since it will be moving back over water soon, it could re-strengthen. However, none of the intensity models show much strengthening, in fact, most of them show Gamma gradually weakening throughout the forecast period. On one hand, the storm is going to be over the warm Gulf of Mexico waters for several days, which favors strengthening. On the other hand, there is a fair amount of dry air over the western Gulf of Mexico and this could entrain into the circulation. Another complicated factor is how Gamma interacts with a developing low over the northwestern Caribbean Sea and a disturbance to its south. Based on these complexities, the NHC intensity forecast shows no change in strength through the forecast period, and lies near the high end of the guidance near the SHIPS model. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America. 2. Even though Gamma is inland, tropical storm conditions will continue across portions of the Yucatan Peninsula tonight and Sunday. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 21.3N 88.0W 50 KT 60 MPH 12H 04/1200Z 21.8N 88.2W 50 KT 60 MPH 24H 05/0000Z 22.2N 88.5W 50 KT 60 MPH 36H 05/1200Z 22.1N 88.9W 50 KT 60 MPH 48H 06/0000Z 21.8N 89.9W 50 KT 60 MPH 60H 06/1200Z 21.3N 90.9W 50 KT 60 MPH 72H 07/0000Z 20.7N 91.7W 50 KT 60 MPH 96H 08/0000Z 20.0N 92.5W 50 KT 60 MPH 120H 09/0000Z 19.9N 93.3W 50 KT 60 MPH $$ Forecaster Cangialosi |