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TROPICAL STORM DARBY DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
900 AM MDT WED JUL 13 2016

About 10-15 kt of northeasterly shear continues to affect Darby,
keeping it just below hurricane strength.  Microwave data
from a few hours ago revealed that the cyclone has a closed
mid-level ring, which is offset a bit from the low-level center.  In
addition, the bulk of the deep convection is displaced to the south
of the center.  Given the current structure, and that Dvorak
estimates range from 55 kt to 65 kt, the initial intensity is held
at 60 kt for now.  Ocean temperatures near Darby are between 28 and
29 degrees Celsius, and based on the forecast track, it appears that
the cyclone will skirt along the northern edge of the cold wake left
behind by previous hurricanes. The SSTs will be sufficiently warm to
support intensification for the next three days or so, and vertical
shear is still expected to decrease later today.  Therefore,
strengthening is anticipated, with the NHC official forecast close
to the high end of the intensity guidance for the entire forecast
period.

Darby has been moving south of due west, or 265/9 kt, due to a
strengthening subtropical ridge extending west of northern Mexico.
The ridge is forecast to remain firmly in place through the next 5
days, keeping Darby on a generally westward path.  The GFS
continues to show a weaker ridge compared to the other global
models at the end of the forecast period, but the spread in the
guidance envelope is actually fairly low.  There is high confidence
in the NHC track forecast, which remains near the southern extent
of the model suite and close to a consensus of the GFS and ECMWF.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 15.2N 112.4W   60 KT  70 MPH
 12H  14/0000Z 15.3N 114.1W   70 KT  80 MPH
 24H  14/1200Z 15.6N 116.5W   80 KT  90 MPH
 36H  15/0000Z 15.9N 119.0W   90 KT 105 MPH
 48H  15/1200Z 16.2N 121.3W   90 KT 105 MPH
 72H  16/1200Z 16.8N 125.4W   80 KT  90 MPH
 96H  17/1200Z 17.5N 129.5W   70 KT  80 MPH
120H  18/1200Z 18.5N 133.5W   60 KT  70 MPH

$$
Forecaster Berg

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