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Tropical Depression Twenty Discussion Number   5
NWS National Hurricane Center Miami FL       AL202020
500 PM AST Sun Sep 13 2020
 
The depression's center is a little closer to the deep convection 
compared to this morning, but the overall structure has not changed 
significantly.  Based on this morning's ASCAT pass, and recent 
Dvorak estimates of T2.0 from TAFB and SAB, the initial intensity 
remains 30 kt.  The northerly shear over the system has been 
analyzed to have decreased since this morning (now around 10 kt), 
which is probably why the center is closer to the convection.  The 
shear is forecast to decrease further, and once the depression 
becomes more detached from the ITCZ/monsoon trough, it is expected 
to go through a significant phase of strengthening as it heads west 
toward higher oceanic heat content and a more unstable atmosphere.  
As discussed this morning, the GFS-based SHIPS guidance indicates 
that there is a 50-50 chance that the depression will strengthen 
by at least 65 kt during the next 3 days, which is 10 times higher 
than the climatological mean.  And, all three regional hurricane 
models (HWRF, HMON, and COAMPS-TC), as well as the HCCA aid, show 
the cyclone becoming a major hurricane by the end of the forecast 
period.  As a result, the NHC intensity forecast has been adjusted 
upward and now explicitly shows major hurricane strength on days 4 
and 5.

The motion remains west-northwestward (290/10 kt), with the 
depression located south of a large mid-level high centered over the 
central Atlantic.  This feature should continue driving the system 
westward or west-northwestward for the next 2 days.  After that 
time, the ridge is expected to shift northward, causing the 
potentially strengthening hurricane to move a little slower toward 
the northwest.  Most of the track models are clustered close 
together, although the HWRF remains a southern outlier and the ECMWF 
model is a little slower and on the right side of the envelope.  The 
new NHC track forecast has not moved much from the previous 
prediction and now lies closest to the HFIP Corrected Consensus.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/2100Z 12.7N  37.6W   30 KT  35 MPH
 12H  14/0600Z 13.2N  39.5W   35 KT  40 MPH
 24H  14/1800Z 13.6N  42.1W   45 KT  50 MPH
 36H  15/0600Z 14.1N  44.4W   60 KT  70 MPH
 48H  15/1800Z 14.7N  46.3W   70 KT  80 MPH
 60H  16/0600Z 15.6N  47.7W   80 KT  90 MPH
 72H  16/1800Z 16.8N  49.0W   90 KT 105 MPH
 96H  17/1800Z 19.5N  51.5W  100 KT 115 MPH
120H  18/1800Z 22.5N  54.0W  100 KT 115 MPH
 
$$
Forecaster Berg
 
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