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Tropical Depression Grace Forecast Discussion Number 10
2021-08-15 22:51:33| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Aug 15 2021 000 WTNT42 KNHC 152051 TCDAT2 Tropical Depression Grace Discussion Number 10 NWS National Hurricane Center Miami FL AL072021 500 PM AST Sun Aug 15 2021 An earlier ASCAT pass over Grace suggested that the maximum winds were 25-30 kt and this has been confirmed by observations from a NOAA Hurricane Hunter aircraft. Aircraft and scatterometer data also suggest that the circulation is elongated and disorganized. Based on these data, the system is being downgraded to a 30-kt depression at this time. Since the system is below storm strength and is passing by Puerto Rico, the Tropical Storm Warnings for Puerto Rico and the U.S. Virgin Islands have been discontinued. The island of Hispaniola is kept under a Tropical Storm Watch given the possibility that the system could restrengthen tonight or tomorrow morning before moving over land. Most of the reliable guidance shows little change in strength over the next 2-3 days. This seems reasonable since the circulation will be interacting with the mountainous land mass of Hispaniola and Cuba for the next 72 hours. The official intensity forecast is near or a little above the DSHIPS and LGEM guidance during that time. Some restrengthening is possible later in the forecast period when the system is expected to move over the Gulf of Mexico. However, the global models are not very bullish on intensification in 4-5 days, perhaps due to drier air. The system has moved mainly westward today, but the track models are generally in agreement on a west-northwestward motion over the forecast period. This is consistent with a well-defined mid-level ridge staying in place over the southwestern Atlantic and across Florida during this week. The official track forecast has been shifted a little south of the previous one, following the multi-model consensus. 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 possible over portions of Hispaniola Monday and Monday night. 3. There is a risk of some wind and rainfall impacts across the Turks and Caicos Islands, the Bahamas, Cuba, and Florida, but forecast uncertainty is much higher than usual. Interests in those areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 17.0N 67.3W 30 KT 35 MPH 12H 16/0600Z 17.6N 68.8W 30 KT 35 MPH 24H 16/1800Z 18.2N 71.0W 30 KT 35 MPH...INLAND 36H 17/0600Z 19.2N 73.2W 30 KT 35 MPH...OVER WATER 48H 17/1800Z 20.2N 75.8W 30 KT 35 MPH...INLAND 60H 18/0600Z 21.0N 78.7W 30 KT 35 MPH...OVER WATER 72H 18/1800Z 22.1N 81.8W 30 KT 35 MPH 96H 19/1800Z 24.0N 87.0W 35 KT 40 MPH 120H 20/1800Z 25.0N 91.0W 45 KT 50 MPH $$ Forecaster Pasch
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