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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.
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
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