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Tropical Depression Grace Forecast Discussion Number 13
2021-08-16 16:55:41| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Aug 16 2021 000 WTNT42 KNHC 161455 TCDAT2 Tropical Depression Grace Discussion Number 13 NWS National Hurricane Center Miami FL AL072021 1100 AM EDT Mon Aug 16 2021 Air Force Reserve and NOAA Hurricane Hunters were both able to locate a center for Grace--probably the most well-defined center observed over the past few days. That center now appears to be moving onshore along the Barahona Peninsula of the Dominican Republic as we speak. The planes measured several possible areas of tropical-storm-force winds from the SFMR, however these observations have not been supported by the more reliable 925-mb flight-level winds for weaker systems, which were only as high as 38 kt, and warrant maintaining the 30-kt initial intensity. Dropsonde data indicate that the central pressure has fallen to 1007 mb. The aircraft fixes confirm that Grace is moving westward, or 280/13 kt. High pressure over the western Atlantic is forecast to slide westward over the southeastern United States during the next several days, which should keep Grace on a westward to west- northwestward trajectory for the entire 5-day forecast period. This scenario is agreed upon by all of the available track models, and the new NHC track forecast has only been nudged slightly southward from the previous forecast based on the latest consensus aids. Grace's intensity forecast remains complicated by interaction with land and the possibility of some westerly shear during the forecast period. However, the southern shift in the forecast track takes the center of Grace more definitively over very warm 30 degrees Celsius waters in the northwestern Caribbean Sea. Therefore, gradual strengthening is anticipated while Grace approaches the Yucatan coast of Mexico. Once the system reaches the Gulf of Mexico, the shear appears to decrease, and conditions there will likely be conducive for additional strengthening. In fact, many of the models, including the consensus aids, bring Grace to hurricane intensity, and the NHC intensity forecast has therefore been bumped upward, bringing Grace very near hurricane strength by the end of the forecast period. Key Messages: 1. Heavy rainfall across the Dominican Republic, Haiti, Cuba, Jamaica, and the Cayman Islands may lead to flash, urban, and small stream flooding, with the potential for mudslides highest in Haiti and the Dominican Republic. 2. Tropical storm conditions are possible over portions of Hispaniola today and tonight, and over Jamaica on Tuesday. Tropical storm conditions are expected over portions of the southern coast of Cuba on Tuesday, spreading westward to the Cayman Islands and other portions of the southern coast of Cuba Tuesday evening through Wednesday morning. 3. There is a increasing risk of wind and rainfall impacts over the Yucatan Peninsula of Mexico Wednesday night and Thursday. Interests there areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 17.7N 71.4W 30 KT 35 MPH 12H 17/0000Z 18.2N 73.4W 30 KT 35 MPH...S COAST OF HAITI 24H 17/1200Z 18.8N 76.2W 35 KT 40 MPH 36H 18/0000Z 19.4N 79.0W 40 KT 45 MPH 48H 18/1200Z 20.1N 82.1W 45 KT 50 MPH 60H 19/0000Z 20.9N 85.2W 50 KT 60 MPH 72H 19/1200Z 21.6N 88.4W 50 KT 60 MPH...N COAST OF YUCATAN 96H 20/1200Z 22.5N 94.0W 60 KT 70 MPH 120H 21/1200Z 23.0N 98.0W 60 KT 70 MPH...INLAND $$ Forecaster Berg
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