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HURRICANE DARBY DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 AM PDT MON JUL 18 2016

Stable air and cool SSTs are taking a toll on Darby. Although the
system still has a well organized circulation and eye feature, deep
convection has been on a steady decline since the previous advisory.
In fact, the cloud tops are now warmer than -50 deg C.  The initial
wind speed is lowered to 70 kt, based on a blend of the Final T- and
CI-numbers from TAFB and SAB.  Cool water and dry air should
continue to affect Darby during the next few days, which will likely
result in continued weakening.  Beyond that time, SSTs are expected
to increase along the forecast track, but the cyclone will also be
moving into an environment of increasing westerly shear. Given these
mixed signals, little change in strength is shown at the end of the
forecast period.  The NHC intensity forecast is largely an update of
the previous one and is close to the intensity model consensus.

Darby is moving a 275/09 kt, and is being steered by a narrow
mid-level ridge to its north.  A westward to west-northwestward
motion at a slightly faster pace is forecast during the 2 to 3 days
while the ridge remains in place. After that time, a motion slightly
south of due west is predicted when a mid-level high builds to the
northwest of the tropical cyclone.  The latest guidance has shifted
a little to the north this cycle, and the NHC official track
forecast has been nudged in that direction. Based on this forecast,
a much weaker Darby could be approaching the Hawaiian Islands at the
end of the period.

An ASCAT-B pass around 0615 UTC was helpful in estimating the wind
radii of Darby.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 18.5N 130.2W   70 KT  80 MPH
 12H  18/1800Z 18.8N 131.8W   60 KT  70 MPH
 24H  19/0600Z 19.3N 134.1W   55 KT  65 MPH
 36H  19/1800Z 19.8N 136.4W   50 KT  60 MPH
 48H  20/0600Z 20.0N 138.7W   45 KT  50 MPH
 72H  21/0600Z 19.6N 143.2W   40 KT  45 MPH
 96H  22/0600Z 18.6N 148.0W   35 KT  40 MPH
120H  23/0600Z 18.3N 151.8W   35 KT  40 MPH

$$
Forecaster Cangialosi

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