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Hurricane Grace Forecast Discussion Number 24
2021-08-19 10:55:45| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Thu Aug 19 2021 000 WTNT42 KNHC 190855 TCDAT2 Hurricane Grace Discussion Number 24 NWS National Hurricane Center Miami FL AL072021 400 AM CDT Thu Aug 19 2021 After a brief convective hiatus between 0400-0700 UTC, deep convection in the inner-core region has increased and become better organized during the past couple of hours. An Air Force Reserve Hurricane Hunter aircraft investigating Grace more than 4 hours ago reported a central pressure of 986 mb -- down 2 mb from previous passes -- and a maximum 700-mb flight-level wind speed of 74 kt on its last leg northbound around 0500 UTC. The 74-kt flight-level wind equates to about a 67-kt surface wind speed. These data supported maintaining a 70-kt intensity at 0600 UTC. The upper-level outflow remains symmetrical and has been expanding somewhat over the past few hours. The initial motion is 280/15 kt based on the earlier recon fixes and passive microwave satellite data. Grace should continue to move generally westward for the next 48 hours, crossing the coast of the eastern Yucatan Peninsula within the next couple of hours, followed by a track across the Yucatan and emergence over the Bay of Campeche by 24 hours, with a subsequent landfall along the eastern coast of mainland Mexico shortly after the 48-hour forecast period. This track scenario is consistent with the latest 0000 UTC global and regional models, which show the strong deep-layer ridge to the north of Grace maintaining its expansive presence across the western Atlantic, Gulf of Mexico, and northern Mexico. After the second landfall, Grace is expected to turn west-southwestward and dissipate over the mountains of central Mexico by 72 hours. The new NHC forecast track is similar to the previous advisory track, and lies along the northern edge of the tightly packed consensus track models. Given the recent improvement in Grace's inner-core convective structure noted in high-resolution infrared satellite imagery, some slight strengthening to 75 kt could still occur just prior to landfall this morning. Weakening will commence once Grace moves inland over Yucatan, with re-strengthening expected after the cyclone emerges over the Bay of Campeche where the vertical wind shear is forecast to decrease below 10 kt. Grace is expected to be a hurricane when the second landfall occurs along the coast of mainland Mexico, with the cyclone possibly reaching a peak intensity of 75 kt shortly after the 48-hour period. After final landfall in mainland Mexico, Grace should quickly weaken and dissipate over the mountains of Mexico by 72 hours, if not sooner. The remnants of Grace are expected to emerge over the eastern North Pacific and possibly re-develop there, but the uncertainty of whether this will be the original center or a new center precludes forecast points over the Pacific at this time. A Hurricane Warning will likely be required for portions of the Hurricane Watch area of mainland Mexico later this morning or afternoon. 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 during the next several hours. 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 is in effect for part of this area. 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 19/0900Z 20.0N 87.2W 70 KT 80 MPH 12H 19/1800Z 20.3N 89.7W 50 KT 60 MPH...INLAND 24H 20/0600Z 20.6N 92.6W 60 KT 70 MPH...OVER WATER 36H 20/1800Z 20.5N 95.0W 70 KT 80 MPH 48H 21/0600Z 20.1N 97.3W 55 KT 65 MPH...INLAND 60H 21/1800Z 19.7N 100.1W 20 KT 25 MPH...POST-TROP/INLAND 72H 22/0600Z...DISSIPATED $$ Forecaster Stewart
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