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Tropical Storm Grace Forecast Discussion Number 9
2021-08-15 16:57:56| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Aug 15 2021 000 WTNT42 KNHC 151457 TCDAT2 Tropical Storm Grace Discussion Number 9 NWS National Hurricane Center Miami FL AL072021 1100 AM AST Sun Aug 15 2021 Grace remains a disorganized system, with only slight evidence of curved bands of deep convection on satellite imagery. WSR-88D radar data from San Juan show broad rotation of the precipitation echoes, but no definite center. The advisory intensity is kept at 35 kt in agreement with Dvorak T-numbers from TAFB. We are waiting for additional observations in the system from an upcoming NOAA Hurricane Hunter mission into Grace in a few hours. Grace is in an environment of moderate shear and reasonably moist mid-level environmental air. Therefore some strengthening is expected before the system reaches Hispaniola tomorrow morning. Thereafter, the future intensity of Grace is dependent on how much the circulation interacts with the islands of the Greater Antilles. Weakening is likely due to the expected passage over the mountainous terrain of Hispaniola, and some restrengthening could occur if the center emerges over water near the Windward Passage. Grace is forecast to maintain minimal tropical storm strength while moving near the northern coast of Cuba. There is, however, considerable uncertainty in the intensity forecast in 2-5 days. The initial motion estimate is a slightly slower 285/14 kt. A well-defined mid-level high pressure system over the southwestern Atlantic should maintain a general west-northwestward motion for the next several days. The global models are in reasonable agreement on a track near/over the Greater Antilles, including Cuba, during the next several days and over the central Gulf of Mexico in the latter part of the forecast period. The official forecast has been changed little from the previous one and is very close to the latest multi-model consensus, TVCA, solution. Key Messages: 1. Heavy rainfall could lead to flash and urban flooding over the Virgin Islands. Across Puerto Rico, the Dominican Republic and Haiti, heavy rainfall may lead to flash, urban and small stream flooding, along with the potential for mudslides. 2. Tropical storm conditions are expected over portions of the Virgin Islands and Puerto Rico today. Tropical storm conditions are expected over parts of the Dominican Republic tonight and Monday. Tropical storm conditions are possible over northwestern portions of the Dominican Republic and Haiti Monday and Monday night. 3. There is a risk of wind and rainfall impacts across the rest of the Dominican Republic, Haiti, the Turks and Caicos Islands, the Bahamas, Cuba, and Florida, but forecast uncertainty remains higher than usual. Interests in those areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 17.2N 66.0W 35 KT 40 MPH 12H 16/0000Z 17.8N 67.8W 40 KT 45 MPH 24H 16/1200Z 18.5N 69.7W 45 KT 50 MPH...INLAND 36H 17/0000Z 19.3N 71.7W 30 KT 35 MPH...INLAND 48H 17/1200Z 20.3N 74.0W 35 KT 40 MPH...OVER WATER 60H 18/0000Z 21.3N 76.6W 35 KT 40 MPH...NEAR N. COAST OF CUBA 72H 18/1200Z 22.3N 79.4W 35 KT 40 MPH...INLAND 96H 19/1200Z 24.6N 84.7W 45 KT 50 MPH...OVER WATER 120H 20/1200Z 26.5N 89.0W 55 KT 65 MPH $$ Forecaster Pasch
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