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Tropical Depression Grace Forecast Discussion Number 14
2021-08-16 22:48:48| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Aug 16 2021 000 WTNT42 KNHC 162048 TCDAT2 Tropical Depression Grace Discussion Number 14 NWS National Hurricane Center Miami FL AL072021 500 PM EDT Mon Aug 16 2021 Grace may have regained tropical storm status just before the center moved across the Barahona Peninsula of the Dominican Republic around midday. The Air Force Reserve Hurricane Hunters measured peak 925-mb winds of 45 kt very near the coast, which would equate to an intensity right at the threshold of tropical storm. Since then, however, land interaction has likely weakened these winds, and Grace is still estimated to be a 30-kt depression. The center appears to have moved back over water just to the south of the Haitian coast. Grace has been moving a little slower today, possibly due to interaction with the terrain of Hispaniola, and the initial motion is estimated to be 285/11 kt. A mid-level high centered over the western Atlantic is forecast to build westward over the southeastern United States and northern Gulf of Mexico in the coming days. This pattern should keep Grace on a westward to west-northwestward trajectory for the entire 5-day forecast period, moving across the northwestern Caribbean Sea, across the northern Yucatan Peninsula, and into the southwestern Gulf of Mexico. The most significant model trends are on days 4 and 5, when many of the track models are indicating a slight west-southwest bend as the cyclone approaches mainland Mexico. The NHC track forecast has been nudged southward at most forecast times, but that may be within the noise level of typical model run-to-run variability. Once the center of Grace moves away from Hispaniola tomorrow, the deep, warm waters of the northwestern Caribbean Sea and relatively light deep-layer shear should be conducive for strengthening. Model data suggest that some mid-level shear could come into play at times, so it's not a sure bet that conditions will be ideal for significant strengthening. Partly for that reason, the NHC intensity forecast is near or just below the intensity consensus. However, even this new forecast is a little higher than the previous forecast, and many of the models indicate that Grace could be near or at hurricane strength when it approaches the Yucatan Peninsula in about 60 hours. After passing the Yucatan Peninsula, additional strengthening is likely, and the new forecast now explicitly shows Grace reaching hurricane intensity over the southwestern Gulf of Mexico. 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 this evening 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 possibly other portions of the southern coast of Cuba Tuesday evening through Wednesday morning. 3. There is a increasing risk of wind, rainfall, and storm surge impacts on 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 16/2100Z 17.9N 72.4W 30 KT 35 MPH 12H 17/0600Z 18.3N 74.4W 30 KT 35 MPH...NEAR SW TIP OF HAITI 24H 17/1800Z 18.9N 77.2W 35 KT 40 MPH 36H 18/0600Z 19.6N 80.4W 40 KT 45 MPH...NEAR CAYMAN ISLANDS 48H 18/1800Z 20.2N 83.5W 50 KT 60 MPH 60H 19/0600Z 20.9N 86.7W 60 KT 70 MPH...NEAR YUCATAN COAST 72H 19/1800Z 21.6N 89.9W 60 KT 70 MPH 96H 20/1800Z 22.4N 95.1W 65 KT 75 MPH 120H 21/1800Z 22.4N 98.8W 65 KT 75 MPH...INLAND $$ Forecaster Berg
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