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HURRICANE DARBY DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 AM PDT TUE JUL 19 2016

Although deep convection has been decreasing since the previous
advisory, Darby still has a well-defined and tight circulation. The
initial intensity is held at 65 kt, in agreement with the Dvorak
CI-numbers from TAFB and SAB, but the automated values from CIMSS at
the University of Wisconsin suggest that this estimate could be a
little generous.

Microwave data indicate that the low-level center of Darby is
located to the south of the eye feature seen in infrared satellite
images, which is likely the result of southerly shear. Using the
microwave fixes, the initial motion estimate is 285/11 kt. A
continued west-northwestward motion is expected today, followed by a
motion slightly south of due west on Wednesday while Darby is
steered by a narrow mid-level ridge to its north. By the end of the
forecast period, a turn to the northwest is predicted when Darby
approaches a trough to the north of the Hawaiian Islands.  The new
NHC track forecast is slightly faster than the previous one to
come in line with latest runs of the GFS and ECMWF models.

Darby is expected to remain over cool water for the next few days,
before it tracks over SSTs around 26 deg C to the east of the
Hawaiian Islands.  However, the system will also be moving into an
environment of increasing southwesterly shear by the time it reaches
the warmer water.  Therefore, gradual weakening is predicted through
the period.  This forecast is the same as the previous one and is in
best agreement with the LGEM guidance.

An ASCAT-B pass from around 0600 UTC was helpful in estimating the
size of Darby's wind field.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 19.4N 134.4W   65 KT  75 MPH
 12H  19/1800Z 19.8N 136.1W   60 KT  70 MPH
 24H  20/0600Z 20.0N 138.3W   55 KT  65 MPH
 36H  20/1800Z 20.0N 140.5W   50 KT  60 MPH
 48H  21/0600Z 19.8N 142.8W   45 KT  50 MPH
 72H  22/0600Z 19.3N 147.3W   35 KT  40 MPH
 96H  23/0600Z 19.4N 150.9W   35 KT  40 MPH
120H  24/0600Z 20.5N 153.0W   30 KT  35 MPH

$$
Forecaster Cangialosi

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