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Tropical Storm Grace Forecast Discussion Number 25
2021-08-19 16:44:18| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Thu Aug 19 2021 000 WTNT42 KNHC 191444 TCDAT2 Tropical Storm Grace Discussion Number 25 NWS National Hurricane Center Miami FL AL072021 1000 AM CDT Thu Aug 19 2021 Grace made landfall as a hurricane near Tulum, Mexico around 0945 UTC (445am CDT). A storm chaser in Tulum reported a minimum pressure of 983 mb at the time of landfall. Since then, the cyclone has moved further inland where observations are far more sparse, and we have no recent in situ observations to assist the intensity analysis. The intensity is therefore set at 55 kt, based in part on the inland decay wind model built into the SHIPS model. The central pressure estimate of 995 mb is likewise uncertain. Some additional weakening is likely this afternoon while Grace continues to cross the Yucatan peninsula. The tropical storm should emerge over the southern Gulf of Mexico this evening, and re-strengthening is anticipated shortly thereafter. Environmental conditions are expected to be quite conducive for strengthening, but it will likely take Grace at least a little time to redevelop its inner-core after disruption by land. That could act to limit the rate at which the cyclone will intensify at first. The HWRF and HMON both suggest that the most significant reintensification could occur in the last 12 hours before final landfall occurs in mainland Mexico, and that scenario seems likely. It would not be surprising if Grace strengthened slightly more between the 36 h forecast point over water and the 48 h point inland, particularly if the hurricane moves slightly slower, giving it more time over the warm waters of the southern Gulf of Mexico. After landfall, Grace should quickly weaken and dissipate over the mountainous terrain of Mexico. Overall, the NHC intensify forecast is very similar to the previous advisory. Grace continues to move to the west near 16 kt. A westward or west-northwestward motion is likely for the next 12 hours or so, after which a strong-deep layer ridge extending well over the northern Gulf of Mexico and southern U.S. will steer Grace westward until landfall. Only minor adjustments were made to the official track forecast, which remains near the multi-model consensus. Although the tropical cyclone will quickly dissipate after it moves inland, the ridge will likely steer its remnants further westward toward the eastern North Pacific, where it could contribute to the formation of a new tropical cyclone there. Key Messages: 1. Tropical storm conditions will continue today across the northern Yucatan Peninsula. 2. Hurricane conditions and dangerous storm surge is likely along portions of eastern mainland Mexico beginning late Friday. A Hurricane Warning is in effect from Puerto Veracruz northward to Cabo Rojo. 3. Through the weekend, heavy rainfall across central and northern portions of the Yucatan Peninsula and Veracruz State should lead to flash and urban flooding. In addition, the heavy rainfall from Grace will be capable of producing mudslides in Veracruz. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 20.2N 88.8W 55 KT 65 MPH 12H 20/0000Z 20.6N 91.2W 55 KT 65 MPH...OVER WATER 24H 20/1200Z 20.6N 94.0W 65 KT 75 MPH 36H 21/0000Z 20.4N 96.3W 75 KT 85 MPH 48H 21/1200Z 20.0N 98.7W 40 KT 45 MPH...INLAND 60H 22/0000Z 19.6N 101.7W 25 KT 30 MPH...POST-TROP/INLAND 72H 22/1200Z...DISSIPATED $$ Forecaster Zelinsky
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