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HURRICANE DARBY DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
800 PM PDT FRI JUL 15 2016

Darby's eye became a little less well-defined and central
convection weakened somewhat a few hours ago, and Dvorak data
T-number from both TAFB and SAB were lowered to 4.5.  Recently,
however, cloud tops have been cooling around the eye and based on
the Dvorak Current Intensity rules the maximum winds are kept at 90
kt for this advisory.  The hurricane has well-defined upper-level
outflow over all but the southeastern portion of the circulation.

The tropical cyclone is in a weak-shear environment and is likely
to remain so for the next several days.  Whereas this would seem to
favor the system to maintain strength or even intensify further,
the future thermodynamic environment is not favorable.  Darby is
approaching a cold tongue in the ocean and should pass over SSTs
near 24 deg C within a couple of days.  Satellite imagery also shows
an extensive stratocumulus field ahead of the hurricane, which is
indicative of stabler air.  These factors should cause Darby to
be on a weakening trend very soon.  The official intensity forecast
is in close agreement with the model consensus, IVCN, and with the
previous NHC forecast.

Darby has moved a little more to the right of the previous track
over the past several hours, but using a 12-hour average yields a
motion estimate of 295/8.  The mid-level flow on the south side of
a subtropical ridge should cause the tropical cyclone to turn
westward over the next several days.  A slight northward adjustment
was made to the official forecast, mainly due to the more northward
short-term motion of Darby.  The new official forecast lies on the
southern side of the guidance envelope and is close to the latest
GFS and ECMWF solutions, which are themselves in close agreement.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 17.3N 122.1W   90 KT 105 MPH
 12H  16/1200Z 17.7N 123.4W   85 KT 100 MPH
 24H  17/0000Z 18.1N 125.1W   80 KT  90 MPH
 36H  17/1200Z 18.4N 126.7W   75 KT  85 MPH
 48H  18/0000Z 18.7N 128.8W   70 KT  80 MPH
 72H  19/0000Z 19.3N 133.3W   55 KT  65 MPH
 96H  20/0000Z 20.0N 138.0W   45 KT  50 MPH
120H  21/0000Z 20.0N 142.5W   40 KT  45 MPH

$$
Forecaster Pasch

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