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Tropical Depression NINE

Tropical Depression Nine Discussion Number   1
NWS National Hurricane Center Miami FL       AL092021
1100 AM EDT Thu Aug 26 2021
Early morning visible satellite imagery shows that the circulation 
associated with the area of low pressure over west-central 
Caribbean Sea has become better defined. There has also been an 
increase in the organization of the associated convective activity, 
and based on consensus Dvorak T-numbers of 2.0 from TAFB and SAB, 
advisories are being initiated on a tropical depression. The initial 
intensity is set at 30 kt, in agreement with the subjective 
satellite estimates.  The official reporting station in Kingston, 
Jamaica, has reported sustained winds of 25 kt with gusts to 35 kt 
during the past couple of hours. An Air Force Reserve 
reconnaissance aircraft is scheduled to be in the system later this 
afternoon to provide more information on the system's structure 
and intensity. 

The depression is moving northwestward or 325/11 kt, however the 
initial motion is a bit more uncertain than normal since the low-
level center has only recently formed.  The cyclone is forecast 
to move steadily northwestward around the southwestern portion of a 
deep-layer ridge centered over the western Atlantic.  This track 
should bring the center near or over western Cuba late Friday,  
over the southeastern and central Gulf of Mexico Friday night and 
Saturday, and have the center approach the northern Gulf coast on 
Sunday.  The track guidance is in relatively good agreement, however 
the average NHC track forecast error at day 4 is around 175 miles, 
so users should not focus on the details of the long range track 
forecast. Some shifts in the track are likely until the system 
consolidates and becomes better defined. The NHC track is near the 
various consensus model aids and is in best agreement with the GFS 
ensemble mean.  

The depression will be moving over the high ocean heat content 
waters of the northwestern Caribbean Sea during the next 24-36 
hours.  This, in combination with low vertical wind shear and a 
moist environment, should allow for steady strengthening.  The 
depression is forecast to become a tropical storm later today or 
tonight, and could approach hurricane strength as it passes near 
or over western Cuba.  Once the system moves into the Gulf of 
Mexico, conditions are expected to be conducive for additional 
strengthening, and rapid intensification is explicitly shown in 
the NHC forecast between 48 and 72 hours. The NHC intensity forecast 
brings the system near major hurricane strength when it approaches 
the northern Gulf coast on Sunday. This forecast is supported by the 
HWRF and CTCI models, and the GFS, ECMWF, and UKMET global model 
guidance, which all significantly deepen the cyclone over the Gulf 
of Mexico.  As a result, there is higher-than-normal confidence 
that a strengthening tropical cyclone will be moving over the Gulf 
this weekend. 

Key Messages:

1. Tropical storm conditions are likely in portions of the Cayman 
Islands tonight and western Cuba Friday and Friday night, with 
dangerous storm surge possible in portions of western Cuba, 
including the Isle of Youth, in areas of onshore flow. 

2. The system is expected to produce life-threatening heavy rains, 
flash flooding and mudslides across Jamaica, the Cayman Islands, 
western Cuba, including the Isle of Youth and northeastern portions 
of the Yucatan Peninsula.  

3. This system is forecast to approach the northern Gulf Coast at or 
near major hurricane intensity on Sunday, although the forecast 
uncertainty is larger than usual since the system is just forming. 
There is a risk of life-threatening storm surge, damaging 
hurricane-force winds, and heavy rainfall Sunday and Monday along 
the northern Gulf Coast from the Florida Panhandle to the upper 
Texas coast, with the greatest risk along the coast of Louisiana.  
Interests in these areas should closely monitor the progress of this 
system and ensure they have their hurricane plan in place.

INIT  26/1500Z 16.9N  79.2W   30 KT  35 MPH
 12H  27/0000Z 18.2N  80.4W   35 KT  40 MPH
 24H  27/1200Z 20.3N  82.0W   45 KT  50 MPH
 36H  28/0000Z 22.5N  83.9W   55 KT  65 MPH...INLAND
 48H  28/1200Z 24.4N  86.0W   65 KT  75 MPH...OVER WATER
 60H  29/0000Z 26.1N  88.1W   80 KT  90 MPH
 72H  29/1200Z 27.7N  90.0W   95 KT 110 MPH
 96H  30/1200Z 30.5N  92.0W   70 KT  80 MPH...INLAND
120H  31/1200Z 33.7N  91.2W   30 KT  35 MPH...INLAND
Forecaster Brown