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Tropical Depression GRACE

Tropical Depression Grace Discussion Number  15
NWS National Hurricane Center Miami FL       AL072021
1100 PM EDT Mon Aug 16 2021
IR and microwave imagery during the past few hours indicate that 
Grace's convective organization has improved a little since this 
afternoon. However, it is currently unknown if that has translated 
to a better-defined surface wind field. Dvorak intensity estimates 
from TAFB and SAB at 00Z supported tropical storm strength, and it 
is possible Grace has redeveloped sustained winds of that magnitude. 
 A hurricane hunter aircraft is scheduled to investigate Grace in a 
few hours, so it seems prudent to avoid making a big change before 
the plane gets there. Grace is therefore conservatively maintained 
as a 30 kt depression for this advisory. Regardless of Grace's exact 
intensity right now, the immediate threat is still torrential 
rainfall across Hispaniola overnight, which will likely cause severe 
flooding in some locations.
The initial motion estimate is 280/12 kt. Confidence in the track 
forecast has increased considerably during the past 24 h and the 
track model spread is low. A mid-level ridge is forecast to build 
over the Gulf of Mexico during the next several days, which should 
keep Grace on a generally westward or west-northwestward track 
through day 5. Once Grace moves away from Haiti, it should remain 
over water until it reaches the Yucatan peninsula late Wednesday or 
early Thursday. Very little change was made to the official track 
forecast, which is based primarily on the multi-model consensus 

Now that Grace is forecast to avoid all major land masses for the 
next couple of days, all of the intensity guidance calls for some 
strengthening to occur. That said, with the exception of the 
COAMPS-TC model, the intensity guidance as a whole shows a slower 
rate of strengthening than it did 6 h ago. The NHC forecast is now 
very near the IVCN intensity consensus throughout the forecast, 
including over the Gulf of Mexico where it continues to show Grace 
reaching hurricane strength. Despite the slightly lower guidance for 
this forecast, it still can not be ruled out that Grace will reach 
hurricane strength over the western Caribbean. When the hurricane 
hunter aircraft reaches Grace in a couple hours and provides more 
information about the current organization of cyclone, we should 
have a better feel for how quickly it could intensify prior to 
reaching the coast of Mexico.
Key Messages:
1. Heavy rainfall across the Dominican Republic, Haiti, Cuba, 
Jamaica, the Cayman Islands, and the northern Yucatan Peninsula may 
lead to flash, urban, and small stream flooding, with the potential 
for mudslides highest in Haiti and the Dominican Republic.
2. Tropical storm conditions are possible over portions of 
Hispaniola overnight, and over Jamaica on Tuesday. Tropical storm 
conditions are expected over portions of the southern coast of Cuba 
on Tuesday, spreading westward to the Cayman Islands and possibly 
other portions of the southern coast of Cuba Tuesday evening through 
Wednesday morning.
3.  There is a increasing risk of wind, rainfall, and storm surge
impacts on the Yucatan Peninsula of Mexico Wednesday night and
Thursday.  Interests there areas should monitor the progress of
Grace and updates to the forecast.
INIT  17/0300Z 18.2N  73.8W   30 KT  35 MPH
 12H  17/1200Z 18.6N  75.7W   35 KT  40 MPH
 24H  18/0000Z 19.1N  78.8W   40 KT  45 MPH
 36H  18/1200Z 19.7N  82.0W   45 KT  50 MPH
 48H  19/0000Z 20.3N  85.1W   50 KT  60 MPH
 60H  19/1200Z 21.0N  88.2W   50 KT  60 MPH...INLAND
 72H  20/0000Z 21.6N  91.3W   55 KT  65 MPH...OVER WATER
 96H  21/0000Z 22.2N  95.9W   65 KT  75 MPH
120H  22/0000Z 22.5N 100.0W   40 KT  45 MPH...INLAND
Forecaster Zelinsky