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| #1019999 (Received by flhurricane at: 11:00 AM 05.Oct.2020) TCDAT5 Tropical Storm Gamma Discussion Number 13 NWS National Hurricane Center Miami FL AL252020 1000 AM CDT Mon Oct 05 2020 Air Force Reserve reconnaissance aircraft investigating Gamma found maximum 850 mb flight-level winds of 37 kt and surface SFMR peak winds of 40 kt, and the central pressure has increased to 1003 mb. Therefore, the initial intensity is lowered to 40 kt for this advisory. Stiff, persistent southerly shear, and an inhibiting thermodynamic surrounding environment should prevent Gamma from restrengthening, although, the Decay SHIPS intensity model does indicate a very brief period of decreasing shear magnitude just prior to landfall around the 24 hour period. Afterward, the shear, once again, increases. Gamma is expected to make landfall over the northwestern Yucatan peninsula on Tuesday and further weakening to a remnant low is forecast Wednesday as the cyclone remains inland over the northern Mexican State of Yucatan. Dissipation is likely to occur Friday over the region, if not sooner. The initial motion is estimated to be a south-southwestward drift, or 205/2 kt. A turn southwestward or west-southwestward is expected by tonight and this general motion should continue through Wednesday morning while moving inland over the northern Mexican State of Yucatan. The large-scale models still insist on some binary interaction occurring with Tropical Storm Delta commencing Tuesday night/Wednesday morning. This should cause Gamma to gradually turn cyclonically through Thursday while remaining over the Northern Yucatan peninsula. If there is a delay in Gamma`s landfall, or the cyclone does remain just offshore, similar to the outlier UKMET, then Tropical Storm Delta could end up absorbing the smaller Gamma tropical cyclone toward the end of the week. For now, the NHC forecast will side with a landfall scenario which agrees with the HCCA consensus and the GFS/ECMWF solutions. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall through midweek over portions of southeast Mexico, including the Mexican states of Yucatan, Campeche, and Tabasco. This rainfall could result in significant flash flooding. 2. Even though Gamma is just offshore, tropical storm conditions are likely along portions of the northern coast of the Yucatan Peninsula later today. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 22.3N 87.6W 40 KT 45 MPH 12H 06/0000Z 22.1N 88.4W 40 KT 45 MPH 24H 06/1200Z 21.6N 89.2W 35 KT 40 MPH 36H 07/0000Z 20.9N 89.9W 30 KT 35 MPH...INLAND 48H 07/1200Z 20.2N 90.2W 25 KT 30 MPH...POST-TROP/INLAND 60H 08/0000Z 20.3N 89.8W 25 KT 30 MPH...POST-TROP/INLAND 72H 08/1200Z 21.0N 89.5W 20 KT 25 MPH...POST-TROP/INLAND 96H 09/1200Z...DISSIPATED $$ Forecaster Roberts |