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HURRICANE DARBY DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 PM PDT SAT JUL 16 2016

Darby appears to have been strengthening during the day despite
moving over increasingly cooler waters.  The deep convection is
becoming more symmetric, the eye has been warming intermittently,
and the hurricane appears to be losing some of its outer banding.
In fact, Darby has developed a marginal annular structure.  Dvorak
estimates have generally risen since this morning, and the initial
intensity is raised to 100 kt.  This makes Darby the second major
hurricane of the eastern North Pacific season.

Sea surface temperatures beneath Darby are currently around 25.5C
and will continue to decrease over the next few days.  But, given
that vertical shear is expected to remain low through at least day
3, and the hurricane's marginal annular structure, Darby is likely
to remain relatively steady in intensity or only gradually weaken in
the short-term.  Faster weakening is still expected later in the
forecast period due to the added effect of increasing shear.
Almost every reliable intensity model shows Darby weakening fast
during the next day or two.  However, the HWRF model is a notable
outlier and keeps Darby as a hurricane at least through day 3.  The
updated NHC intensity forecast is a little higher than the previous
forecast during the first 36 hours and is near the top end of the
main pack of intensity models.

The initial motion remains 285/9 kt.  The subtropical ridge to the
north of Darby is weakening, but it should stay strong enough to
steer the hurricane west-northwestward or westward through the
entire forecast period.  The new run of the ECMWF has sped up
compared to the other track models, but otherwise there is very
little spread in the guidance envelope.  The updated NHC track
forecast is closest to an average of the GFS and ECMWF and is very
close to the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 18.0N 124.9W  100 KT 115 MPH
 12H  17/0600Z 18.3N 126.3W   90 KT 105 MPH
 24H  17/1800Z 18.5N 128.1W   80 KT  90 MPH
 36H  18/0600Z 18.8N 130.1W   70 KT  80 MPH
 48H  18/1800Z 19.0N 132.2W   60 KT  70 MPH
 72H  19/1800Z 19.7N 136.6W   50 KT  60 MPH
 96H  20/1800Z 19.7N 141.1W   40 KT  45 MPH
120H  21/1800Z 18.7N 146.0W   35 KT  40 MPH

$$
Forecaster Berg

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