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Tropical Storm Gamma Forecast Discussion Number 9
2020-10-04 16:43:47| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sun Oct 04 2020 000 WTNT45 KNHC 041443 TCDAT5 Tropical Storm Gamma Discussion Number 9 NWS National Hurricane Center Miami FL AL252020 1000 AM CDT Sun Oct 04 2020 An Air Force Reserve reconnaissance aircraft has found the center of Gamma over the far southern Gulf of Mexico, just north of the Yucatan Peninsula. Early morning visible satellite imagery has revealed decent banding structure over the northern and western portions of the circulation. The aircraft has measured a peak 850 mb flight-level wind of 66 kt and SFMR winds of 47 kt. A blend of these data support an initial intensity of 50 kt, which is also in line with the latest Dvorak classifications of T3.0 and T3.5 from SAB and TAFB, respectively. Gamma appears to be slowing down as anticipated, with an initial motion estimate of 360/3 kt. Gamma is expected to meander over the southern Gulf of Mexico, just north of the northern coast of the Yucatan peninsula during the next 12-24 hours. By late Monday, the western portion of a subtropical ridge is expected to build westward over the northern Gulf of Mexico. This should cause Gamma to turn westward to west-southwestward through the remainder of the forecast period. The dynamical model guidance is in general agreement on this scenario, but there are some differences in how close Gamma tracks to the northwestern portion of the Yucatan peninsula. The NHC track splits these differences and is a blend TCVA multi-model consensus and the HFIP corrected consensus. The new track forecast is very close to the previous official forecast. Although Gamma has re-strengthened this morning, increasing southerly wind shear is expected over the cyclone by tonight. This unfavorable upper-level environment is likely to cause some gradual weakening by late tonight and Monday. Since the vertical shear expected to remain moderate to strong through the latter portion of the forecast period, little overall change in strength is shown after 48 hours. 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 offshore, tropical storm conditions will continue across portions of the northern coast of the Yucatan Peninsula today. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 22.2N 88.2W 50 KT 60 MPH 12H 05/0000Z 22.6N 88.2W 50 KT 60 MPH 24H 05/1200Z 22.6N 88.5W 45 KT 50 MPH 36H 06/0000Z 22.3N 89.3W 40 KT 45 MPH 48H 06/1200Z 22.0N 90.2W 40 KT 45 MPH 60H 07/0000Z 21.5N 91.0W 40 KT 45 MPH 72H 07/1200Z 21.0N 91.6W 40 KT 45 MPH 96H 08/1200Z 20.4N 92.5W 40 KT 45 MPH 120H 09/1200Z 20.4N 93.0W 40 KT 45 MPH $$ Forecaster Brown
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