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HURRICANE DARBY DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
800 PM PDT THU JUL 14 2016

Darby has become a little better organized during the past 6 hours
with a ragged 30-nmi-diameter eye having appeared within the central
dense overcast. Upper-level outflow has continued to expand in all
quadrants. The initial intensity has been increased to 80 kt based
on a blend of consensus subjective intensity estimates of T4.5/77 kt
from TAFB and SAB, and UW-CIMSS objective intensity estimates of 83
kt and 85 kt from AMSU and ADT, respectively.

Darby's initial motion estimate is 280/11 kt after smoothing through
some wobbles in the track. Otherwise, there is no significant change
to previous track or philosophy. The latest model guidance remains
in excellent agreement on Darby moving west-northwestward to
westward for the next 48 hours, followed by a turn to a more due
west motion after that as the ridge to the north of the hurricane
builds slightly southward and westward. The new NHC track forecast
is basically just an extension of the previous advisory track, and
remains near the southern edge of the guidance suite, following the
consensus of the GFS and ECMWF models.

Although the vertical wind shear is expected to remain 10 kt or
less throughout the 5-day forecast period, SSTs decreasing below
27C and the large eye of Darby argue against any significant
strengthening during the next day or so. After that, SSTs
decreasing to less than 26C should induce gradual weakening by 36 h
and beyond. However, the aforementioned weak wind shear conditions
should act to prevent a more typical rapid weakening trend from
occurring. This is similar to the slower-than-normal weakening trend
noted with Tropical Storm Celia during the past couple of days while
that cyclone has been moving through a similar environment of low
shear and cool waters near 25C. The official NHC intensity forecast
is above the IVCN intensity consensus model, and closely follows a
blend of the SHIPS and LGEM models.

FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 16.0N 119.1W   80 KT  90 MPH
 12H  15/1200Z 16.4N 120.7W   85 KT 100 MPH
 24H  16/0000Z 16.9N 122.7W   85 KT 100 MPH
 36H  16/1200Z 17.4N 124.7W   80 KT  90 MPH
 48H  17/0000Z 17.6N 126.5W   75 KT  85 MPH
 72H  18/0000Z 18.1N 130.4W   65 KT  75 MPH
 96H  19/0000Z 18.3N 135.1W   55 KT  65 MPH
120H  20/0000Z 18.6N 140.0W   50 KT  60 MPH

$$
Forecaster Stewart

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