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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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