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Hurricane Darby Discussion Number  15
NWS National Hurricane Center Miami FL       EP052022
500 PM HST Tue Jul 12 2022
 
Darby remains an impressive hurricane in conventional satellite
imagery, however the eye is not as defined as it was earlier today.
As noted in the previous discussion, the hurricane is more
asymmetric with the cloud shield favoring the western semicircle.
A 0043 UTC SSMIS microwave overpass revealed some erosion of the
convection over the northern semicircle which is suggestive of some
dry air entrainment over that portion of the circulation.  A blend 
of the TAFB and SAB subjective Dvorak T- and CI-numbers yields an 
initial intensity of 95 kt. This is also supported by the latest
UW/CIMSS ADT and SATCON estimates which are 95 and 98 kt,
respectively.
 
Although the vertical shear is expected to remain quite low during
the next 24 hours, Darby will be moving over marginal sea surface
temperatures, which is expected to cause gradual weakening. After
that time, a sharp increase in vertical wind shear and SSTs of 24 
to 25 degrees Celsius should result in continued weakening. 
Simulated satellite imagery from the global models suggest Darby 
will cease to produce deep convection in a few days and the NHC 
forecast calls for the system to become a post-tropical cyclone in 
about 72 hours.  The remnant low is expected to degenerate into a 
trough by day 5, and this is reflected in the NHC forecast.  There 
is not much spread in the intensity model guidance and the official 
forecast is in good agreement with the SHIPS, ICON, and HCCA 
intensity aids.
 
Darby remains on a steady westward motion at about 15 kt.  A 
slightly slower westward to west-northwestward track is expected by 
Wednesday as the tropical cyclone nears a break in the subtropical 
ridge. After 48 hours, a weaker Darby should turn back westward as 
the low-level trade wind flow becomes the more dominant steering 
layer. Although there is very little cross-track spread in the 
dynamical model guidance, the envelope has shifted slightly 
southward this cycle, and the NHC forecast has been adjusted 
accordingly.  The new NHC track forecast is near the GFEX and TVCE 
consensus models.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0300Z 14.6N 132.7W   95 KT 110 MPH
 12H  13/1200Z 14.9N 134.8W   85 KT 100 MPH
 24H  14/0000Z 15.4N 137.4W   75 KT  85 MPH
 36H  14/1200Z 16.1N 140.0W   65 KT  75 MPH
 48H  15/0000Z 16.6N 142.4W   55 KT  65 MPH
 60H  15/1200Z 16.8N 145.0W   45 KT  50 MPH
 72H  16/0000Z 16.9N 148.0W   35 KT  40 MPH...POST-TROPICAL
 96H  17/0000Z 16.8N 154.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  18/0000Z...DISSIPATED
 
$$
Forecaster Brown
 
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