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Tropical Storm Grace Forecast Discussion Number 19
2021-08-18 04:48:47| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Tue Aug 17 2021 009 WTNT42 KNHC 180248 TCDAT2 Tropical Storm Grace Discussion Number 19 NWS National Hurricane Center Miami FL AL072021 1100 PM EDT Tue Aug 17 2021 NOAA and Air Force Hurricane Hunter aircraft that have been investigating Grace this evening have found that the center moved off the western tip of Jamaica shortly before 0000 UTC. Radar and conventional satellite imagery, as well as earlier microwave data, show that convective banding has increased with a band that wraps around the eastern and northern portions of the circulation. The Air Force reconnaissance aircraft measured a peak 850-mb flight-level wind of 64 kt, and both aircraft have measured believable SFMR winds of 50-52 kt. Based on those data the maximum winds were increased to 50 kt on the 0000 UTC intermediate advisory, and the initial intensity remains unchanged for this advisory. Grace will be moving over the high ocean heat content waters of the northwestern Caribbean Sea during the next day or so. That, along with generally low to moderate vertical wind shear conditions, should allow for steady strengthening until Grace reaches the coast of the Yucatan Peninsula in just under 36 hours. The NHC intensity forecast call for Grace to become a hurricane on Wednesday, and the storm could peak near category 2 intensity before it reaches the coast of Mexico late Wednesday night or early Thursday. By the 36- hour forecast, some weakening is likely to have occurred as that point is now inland. Some weakening will likely occur while Grace moves over land, but restrengthening is predicted when the storm moves over the Bay of Campeche. The NHC intensity forecast is in best agreement with the HCCA and IVCN consensus aids. Grace has been moving slightly north of due west, or 280/12 kt. A strong deep-layer ridge the extends from the western Atlantic across the eastern and central Gulf of Mexico should continue to steer the tropical storm westward to west-northwestward for the next several days. While the dynamical models agree on this overall forecast scenario, there remains some north-south spread with the HWRF, HMON, and GFS along the northern side of the guidance envelope, taking Grace near the northeastern portion of the Yucatan Peninsula. On the other hand, the UKMET and its ensemble mean depict a more westward track toward the southern portion of the Yucatan Peninsula of Mexico. The NHC forecast splits these differences and lies near the various consensus aids, which were just a tad farther south this cycle. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected over portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico beginning late Wednesday night. 2. Heavy rainfall across Jamaica, the Cayman Islands, and the Yucatan Peninsula is likely to lead to flash and urban flooding. Mudslides are possible in Jamaica. 3. Tropical storm conditions are expected over portions of Jamaica for a few more hours, and over the Cayman Islands later tonight and Wednesday. Hurricane conditions are possible in the Cayman Islands by Wednesday morning. Tropical storm conditions are expected to spread westward from portions of the southern coast of Cuba in the warning area to, possibly, other portions of the southern coast of Cuba in the watch area tonight through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 18.4N 79.2W 50 KT 60 MPH 12H 18/1200Z 18.9N 81.5W 60 KT 70 MPH 24H 19/0000Z 19.5N 84.7W 75 KT 85 MPH 36H 19/1200Z 20.0N 87.8W 80 KT 90 MPH...INLAND 48H 20/0000Z 20.4N 90.7W 50 KT 60 MPH...OVER WATER 60H 20/1200Z 20.7N 93.2W 65 KT 75 MPH 72H 21/0000Z 20.8N 95.6W 75 KT 85 MPH 96H 22/0000Z 20.7N 100.1W 35 KT 40 MPH...INLAND 120H 23/0000Z 20.5N 104.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Brown
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