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| #1057535 (Received by flhurricane at: 11:02 AM 18.Aug.2021) TCDAT2 Hurricane Grace Discussion Number 21 NWS National Hurricane Center Miami FL AL072021 1100 AM EDT Wed Aug 18 2021 Grace is becoming better organized on satellite images with a comma-shaped cloud pattern, and the upper-level outflow remains well defined. Wind gusts well into the hurricane-force range were measured on Grand Cayman earlier this morning, along with some damage on the island. Recent flight-level and SFMR observations from both the Air Force and NOAA Hurricane Hunter aircraft support sustained 65-kt surface winds, so the system is being upgraded to a hurricane on this advisory. Although Grace is situated over waters of very high oceanic heat content, moderate northwesterly shear and only marginally moist mid-level air could slightly impede intensification. However, some additional strengthening is expected before landfall tonight or early Thursday. Weakening will occur due to Grace`s passage over Yucatan, although that land mass has relatively low terrain. Reintensification is anticipated over the Bay of Campeche on Friday, and the system should regain hurricane strength before reaching the east coast of mainland Mexico. The official intensity forecast is similar to the numerical model consensus. Grace has been moving west-northwestward near 13 kt. A prominent mid-tropospheric ridge is likely to remain in place to the north of the cyclone for the next several days. This pattern should keep steering Grace on a west-northwestward to westward track for 72-96 hours. The track guidance models are in excellent agreement and little change has been made to the NHC track forecast compared to the previous few packages. A Hurricane Watch will likely be required for a portion of the coast of eastern mainland Mexico later today. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected in portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico beginning late tonight or early Thursday. Preparations to protect life and property should be rushed to completion. 2. There is an increasing risk of hurricane conditions and dangerous storm surge in portions of eastern mainland Mexico beginning late Friday, and a Hurricane Watch will likely be issued for part of this area later today. 3. Over the next few days, heavy rainfall across the Cayman Islands as well as portions of the Yucatan Peninsula and Veracruz State should lead to flash and urban flooding, with mudslides possible in the Mexican state of Veracruz. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 19.4N 82.2W 65 KT 75 MPH 12H 19/0000Z 19.7N 84.5W 70 KT 80 MPH 24H 19/1200Z 20.3N 87.6W 75 KT 85 MPH...INLAND 36H 20/0000Z 20.6N 90.5W 50 KT 60 MPH...OVER WATER 48H 20/1200Z 20.7N 93.2W 65 KT 75 MPH...OVER WATER 60H 21/0000Z 20.7N 95.3W 75 KT 85 MPH 72H 21/1200Z 20.5N 97.7W 60 KT 70 MPH...INLAND 96H 22/1200Z 20.0N 103.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 23/1200Z...DISSIPATED $$ Forecaster Pasch |