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Tropical Depression Twenty Discussion Number   4
NWS National Hurricane Center Miami FL       AL202020
1100 AM AST Sun Sep 13 2020
 
Convective banding features are generally limited to the southern 
semicircle of the circulation with the center exposed just to the 
north.  A recent ASCAT pass indicated that the strongest winds--up 
to 30 kt--were primarily located in the southerly and southwesterly 
monsoonal flow trailing the depression, although some stronger 
winds are beginning to develop just west of the center.  Light-to- 
moderate northerly shear is currently affecting the depression, but 
this shear is expected to decrease during the next 24-48 hours.  In 
addition, global model fields indicate that the cyclone should 
become increasingly separated from the ITCZ/monsoon trough.  Steady 
strengthening is anticipated for much of the forecast period, and 
the NHC intensity forecast closely follows the HCCA aid and the 
IVCN intensity consensus.  This new forecast is a little higher 
than the previous prediction, especially on days 3 through 5.  
There are two main points that suggest this forecast could 
potentially go even higher in later forecast cycles:  1. the HWRF 
model shows more significant strengthening at the latter part of 
the period, bringing the system to major hurricane strength, and 2. 
the SHIPS Rapid Intensification guidance indicates that there is a 
50-50 chance that the system will strengthen by at least 65 kt over 
the next 3 days, which is 9-10 times higher than the climatological 
mean.

The depression is moving west-northwestward (290/9 kt) to the south 
of a large mid-tropospheric high centered over the central 
subtropical Atlantic.  This feature should continue to drive the 
cyclone westward or west-northwestward for the next 2-3 days.  
After that time, the mid-level high is expected to shift northward 
and elongate, and the potentially intensifying hurricane is likely 
to acquire more poleward motion, moving northwestward and a little 
slower on days 3-5.  Most of the track models are clustered close 
together, except for the HWRF which has a trajectory farther to the 
south and west.  The new NHC track forecast has been shifted a bit 
westward compared to the previous prediction, close to the 
GFS-ECMWF consensus but not as far to the left as the latest TVCA 
and HCCA solutions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/1500Z 12.3N  36.4W   30 KT  35 MPH
 12H  14/0000Z 12.8N  38.0W   35 KT  40 MPH
 24H  14/1200Z 13.3N  40.6W   45 KT  50 MPH
 36H  15/0000Z 13.7N  43.0W   55 KT  65 MPH
 48H  15/1200Z 14.4N  45.1W   65 KT  75 MPH
 60H  16/0000Z 15.3N  46.7W   75 KT  85 MPH
 72H  16/1200Z 16.3N  48.2W   85 KT 100 MPH
 96H  17/1200Z 19.0N  51.0W   95 KT 110 MPH
120H  18/1200Z 22.0N  53.5W   95 KT 110 MPH
 
$$
Forecaster Berg
 
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