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HURRICANE DARBY DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 AM PDT THU JUL 14 2016

Darby continues to generate a large area of cold cloud tops near
the center, and recent microwave images show a mid-level eye is
present.  However, the images also suggest this feature is displaced
to the south or southwest of the low-level center, possibly due to
the effects of northeasterly vertical wind shear. Satellite
intensity estimates from TAFB and SAB remain unchanged at 65 kt, and
earlier AMSU intensity estimates were near 70 kt.  So, the initial
intensity remains 70 kt.

The initial motion is 275/10.  The dynamical models forecast a
large deep-layer ridge over much of the eastern and central Pacific
for the next several days, and this feature should steer Darby
generally westward through the forecast period.  The track guidance
has similar tracks to that of the previous advisory, but it shows
a slightly faster forward speed.  Thus, the new forecast track,
which is a blend of the GFS and ECMWF forecasts, is similar to, but
a little faster than, the previous track.

The current shear should subside in the next 12 hours or so, with
Darby likely to remain in a light shear environment during the
remainder of the forecast period.  Therefore, sea surface
temperature is expected to be the major factor controlling Darby's
intensity.  The hurricane is currently over sea surface temperatures
near 27C, and this should continue for the next 36 hours or so.
During this time, the intensity forecast calls for slow
strengthening.  From 48-72 hours, the forecast track takes Darby
across an area of sea surface temperatures less than 25C, a cold
pool that is poorly resolved in the statistical guidance.  The
intensity forecast calls for significant weakening from 48-72 hours,
with the 72 hour forecast on the low side of the intensity guidance.
After 72 hours, Darby should move over increasing sea surface
temperatures near or parallel to the 26C isotherm. At that time,
though, the cyclone is expected to encounter a drier and more stable
air mass, so the forecast follows the guidance in calling for a
continued slow weakening.


FORECAST POSITIONS AND MAX WINDS

INIT  14/0900Z 15.7N 115.5W   70 KT  80 MPH
 12H  14/1800Z 16.0N 117.5W   75 KT  85 MPH
 24H  15/0600Z 16.4N 119.9W   80 KT  90 MPH
 36H  15/1800Z 16.8N 122.2W   85 KT 100 MPH
 48H  16/0600Z 17.1N 124.2W   85 KT 100 MPH
 72H  17/0600Z 17.5N 128.0W   65 KT  75 MPH
 96H  18/0600Z 18.0N 131.5W   55 KT  65 MPH
120H  19/0600Z 18.5N 136.0W   45 KT  50 MPH

$$
Forecaster Beven

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