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Tropical Depression Fifteen Discussion Number   5
NWS National Hurricane Center Miami FL       AL152023
1100 AM AST Sat Sep 16 2023
 
The tropical depression has not changed much this morning. The 
center remains poorly defined, and visible satellite imagery 
indicates a broad region of low- and mid-level rotation persisting 
over a large area. Most of the deep convection is occurring in the 
northern semicircle of the broad circulation. Subjective Dvorak 
estimates from SAB and TAFB were 25 kt and 35 kt, respectively, and 
are similar to the objective Dvorak estimates. Based on the 
disorganized structure and the current intensity estimates, the 
intensity is held at 30 kt for this advisory. A late arriving ASCAT 
pass suggests that this estimate may be a bit generous.  

Since the center of circulation is broad, the initial motion is 
somewhat uncertain and estimated at 330/16 kt. This general motion 
is expected to continue for the next couple days as the depression 
moves along the southern periphery of a mid-level ridge located to 
the northeast of the system. Track guidance, including global and 
regional hurricane models, is in general agreement that the system 
will continue on a northwestward trajectory for the next several 
days. After 72 hours, the track forecast uncertainty increases 
somewhat as the system will begin to interact with a deep-layer 
trough. This trough interaction is expected to induce a more 
poleward shift in the track and eventually recurve the system toward 
the northeast by 120 hours. The NHC track forecast is similar to the 
prior forecast and in agreement with the consensus aids, TVCN and 
HCCA. 

The system is currently in a favorable environment for 
intensification, with low vertical wind shear and warm sea surface 
temperatures expected to persist during the next several days. 
However, the timing of intensification will depend on how quickly 
the system is able to consolidate into a more compact structure. The 
current intensity forecast assumes that it will take 24-36 hours for 
this to happen, with the system expected to become a hurricane in 48 
hours. The current forecast reaches 95 kt by 72 h, although some of 
the regional hurricane models, including HWRF and HMON, indicate a 
more rapid intensification. ECMWF-SHIPS guidance continues to 
indicate a greater than a 40 percent chance of rapid intensification 
in the next 72 hours. By mid-week, as the system recurves to the 
northeast, it is expected to gradually weaken as southwesterly shear 
increases. The NHC forecast is lower than the regional model 
guidance and is similar to both the prior forecast and HCCA.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/1500Z 19.7N  46.2W   30 KT  35 MPH
 12H  17/0000Z 21.3N  47.4W   35 KT  40 MPH
 24H  17/1200Z 23.2N  49.0W   45 KT  50 MPH
 36H  18/0000Z 24.7N  50.4W   55 KT  65 MPH
 48H  18/1200Z 26.2N  52.2W   65 KT  75 MPH
 60H  19/0000Z 27.5N  54.1W   75 KT  85 MPH
 72H  19/1200Z 28.9N  56.0W   95 KT 110 MPH
 96H  20/1200Z 32.8N  58.3W   90 KT 105 MPH
120H  21/1200Z 37.0N  55.2W   80 KT  90 MPH
 
$$
Forecaster Hogsett/Bucci
 
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