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Tropical Storm Grace Forecast Discussion Number 28
2021-08-20 10:52:38| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Fri Aug 20 2021 000 WTNT42 KNHC 200852 TCDAT2 Tropical Storm Grace Discussion Number 28 NWS National Hurricane Center Miami FL AL072021 400 AM CDT Fri Aug 20 2021 Deep convection has increased near the center of Grace overnight with improved banding structure over the eastern portion of the circulation. An Air Force Reserve Hurricane Hunter aircraft measured a peak 850-mb flight-level wind of 72 kt and SFMR winds of 58 kt during the aircraft's final pass through the northern portion of the storm prior to 06Z. Based on those observations, the initial wind speed was increased to 60 kt on the 06Z intermediate advisory, and it remains at that value for now. Grace is close to re-gaining hurricane strength, and the next reconnaissance mission should be in the storm around 1200 UTC this morning. Grace will be moving over the warm waters over the Bay of Campeche today. That, along with light to moderate vertical wind shear conditions, are expected to allow for re-intensification until landfall in mainland Mexico tonight. The updated intensity forecast brings Grace to a 75-kt hurricane in 12 hours, and the storm could be slightly stronger when it makes landfall overnight. By 24 h, the center is forecast to be inland, and Grace will likely already to have begun to weaken. Rapid weakening should occur on Saturday as Grace moves farther inland over the mountainous terrain of central Mexico, and the circulation is likely to dissipate in around 48 hours. The remnants of Grace are expected to move into the Pacific where they are likely to spawn a new tropical cyclone. The cyclone has been moving westward or 270/14 kt. A strong mid-level ridge to the north of Grace should continue to steer the cyclone westward to west-southwestward until dissipation occurs in a couple days. The new NHC track forecast is near the middle of the guidance envelope and is essentially unchanged from the previous advisory. Key Messages: 1. Hurricane conditions and dangerous storm surge are likely along portions of eastern mainland Mexico beginning late today. A Hurricane Warning is in effect from Puerto Veracruz northward to Cabo Rojo. 2. Through the weekend, heavy rainfall across Veracruz, Puebla, Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi will lead to flash and urban flooding, along with the likelihood of mudslides. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 20.7N 93.3W 60 KT 70 MPH 12H 20/1800Z 20.6N 95.2W 75 KT 85 MPH 24H 21/0600Z 20.3N 97.4W 70 KT 80 MPH...INLAND 36H 21/1800Z 19.8N 99.7W 35 KT 40 MPH...INLAND 48H 22/0600Z 19.4N 102.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 22/1800Z...DISSIPATED $$ Forecaster Brown
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