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Tropical Depression GRACE

Tropical Depression Grace Discussion Number  14
NWS National Hurricane Center Miami FL       AL072021
500 PM EDT Mon Aug 16 2021
Grace may have regained tropical storm status just before the
center moved across the Barahona Peninsula of the Dominican
Republic around midday.  The Air Force Reserve Hurricane Hunters
measured peak 925-mb winds of 45 kt very near the coast, which
would equate to an intensity right at the threshold of tropical
storm.  Since then, however, land interaction has likely weakened
these winds, and Grace is still estimated to be a 30-kt depression.
The center appears to have moved back over water just to the south
of the Haitian coast.
Grace has been moving a little slower today, possibly due to
interaction with the terrain of Hispaniola, and the initial motion
is estimated to be 285/11 kt.  A mid-level high centered over the
western Atlantic is forecast to build westward over the
southeastern United States and northern Gulf of Mexico in the
coming days.  This pattern should keep Grace on a westward to
west-northwestward trajectory for the entire 5-day forecast period,
moving across the northwestern Caribbean Sea, across the northern
Yucatan Peninsula, and into the southwestern Gulf of Mexico.  The
most significant model trends are on days 4 and 5, when many of the
track models are indicating a slight west-southwest bend as the
cyclone approaches mainland Mexico.  The NHC track forecast has
been nudged southward at most forecast times, but that may be
within the noise level of typical model run-to-run variability.
Once the center of Grace moves away from Hispaniola tomorrow, the
deep, warm waters of the northwestern Caribbean Sea and relatively
light deep-layer shear should be conducive for strengthening.
Model data suggest that some mid-level shear could come into play
at times, so it's not a sure bet that conditions will be ideal for
significant strengthening.  Partly for that reason, the NHC
intensity forecast is near or just below the intensity consensus.
However, even this new forecast is a little higher than the
previous forecast, and many of the models indicate that Grace could
be near or at hurricane strength when it approaches the Yucatan
Peninsula in about 60 hours.  After passing the Yucatan Peninsula,
additional strengthening is likely, and the new forecast now
explicitly shows Grace reaching hurricane intensity over the
southwestern Gulf of Mexico.
Key Messages:
1. Heavy rainfall across the Dominican Republic, Haiti, Cuba,
Jamaica, and the Cayman Islands 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 this evening and tonight, 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  16/2100Z 17.9N  72.4W   30 KT  35 MPH
 12H  17/0600Z 18.3N  74.4W   30 KT  35 MPH...NEAR SW TIP OF HAITI
 24H  17/1800Z 18.9N  77.2W   35 KT  40 MPH
 36H  18/0600Z 19.6N  80.4W   40 KT  45 MPH...NEAR CAYMAN ISLANDS
 48H  18/1800Z 20.2N  83.5W   50 KT  60 MPH
 60H  19/0600Z 20.9N  86.7W   60 KT  70 MPH...NEAR YUCATAN COAST
 72H  19/1800Z 21.6N  89.9W   60 KT  70 MPH
 96H  20/1800Z 22.4N  95.1W   65 KT  75 MPH
120H  21/1800Z 22.4N  98.8W   65 KT  75 MPH...INLAND
Forecaster Berg