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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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