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HURRICANE DARBY DISCUSSION NUMBER  24
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
800 AM PDT SUN JUL 17 2016

Darby's satellite presentation has changed very little since the
last advisory.  The hurricane still has a well-defined 10 n mi wide
eye and a symmetric central dense overcast with cloud tops as cold
as -68C.  The initial intensity is held at 85 kt based on a blend
of the latest Dvorak Current Intensity numbers, which are 5.0/90 kt
from TAFB and SAB and 4.7/82 kt from the UW-CIMSS ADT.

A narrow subtropical ridge lies to the north of the hurricane along
30N, which is steering Darby westward, or 280/8 kt.  A westward or
west-northwestward motion is expected during the next four days due
to the position and strength of the ridge, and the track guidance
is in excellent agreement during this period.  By day 5, a weaker
Darby is forecast to turn west-southwestward due to strong
low-level ridging north of the Hawaiian Islands.  There is a little
more spread among the track models at the end of the forecast
period, but the GFS, ECMWF, and UKMET are all south of the TVCE
multi-model consensus.  The updated forecast therefore remains
south of TVCE and is a little faster than the previous forecast on
day 5.

Darby is now over SSTs between 24 and 25C and is expected to move
over even colder waters in 12-24 hours.  Therefore, fairly quick
weakening is forecast in the short term, and Darby is likely to lose
hurricane strength on Monday.  SSTs are actually expected to begin
increasing again after 24 hours, which could slow the rate of
weakening through the end of the forecast period. However,
increasing vertical shear and a drier mid-level air mass by days 4
and 5 will likely prevent significant re-intensification over the
warmer waters to the southeast of Hawaii.  The NHC intensity
forecast is near the SHIPS model through day 3 and then a little
higher than SHIPS on days 4 and 5, closer to the ICON intensity
consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  17/1500Z 18.3N 127.4W   85 KT 100 MPH
 12H  18/0000Z 18.4N 128.8W   75 KT  85 MPH
 24H  18/1200Z 18.8N 130.9W   65 KT  75 MPH
 36H  19/0000Z 19.3N 133.1W   55 KT  65 MPH
 48H  19/1200Z 19.7N 135.4W   50 KT  60 MPH
 72H  20/1200Z 20.1N 140.2W   40 KT  45 MPH
 96H  21/1200Z 19.5N 145.0W   35 KT  40 MPH
120H  22/1200Z 18.5N 150.0W   35 KT  40 MPH

$$
Forecaster Berg

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