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TROPICAL STORM DARBY DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
300 AM MDT WED JUL 13 2016

Darby continues to strengthen.  The satellite appearance has changed
from a shear pattern to a central dense overcast, with a larger and
deeper area of convection than 6 hours ago.  In addition, a WindSat
37 GHz microwave pass at 0104 UTC showed the development of a
low-level ring feature.  The initial wind speed is raised to 60
kt, a bit above the satellite classifications in deference to the
improved inner-core structure.

Somewhat surprisingly, Darby has been rapidly intensifying during
the past 24 hours, with a 30-kt wind increase during that time.
Given the recently observed microwave ring feature and a generally
conducive environment, it makes sense to be on the high side of the
guidance in the near-term.  After 24 hours, SSTs should drop to
around 27C, but the shear is expected to stay low. Thus, the
forecast intensities are leveled off from days 1-3 in agreement with
much of the guidance.  A slow decrease in wind speed is predicted at
long range due to gradually falling SSTs.   The NHC intensity
forecast is most similar to a consensus of the HWRF, SHIPS and LGEM
models.

The storm is moving generally westward at about 10 kt.  This
general motion is expected for the next several days while
Darby remains on the southern side of a strong ridge over the
eastern Pacific.  The cyclone could turn toward the west-northwest
by the end of the period with a weaker ridge possible over the
western portion of the basin. Only small changes were made to the
previous forecast, and the latest NHC prediction is on the southern
side of the well-clustered guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 15.3N 111.5W   60 KT  70 MPH
 12H  13/1800Z 15.3N 113.1W   70 KT  80 MPH
 24H  14/0600Z 15.5N 115.4W   85 KT 100 MPH
 36H  14/1800Z 15.7N 117.9W   90 KT 105 MPH
 48H  15/0600Z 16.0N 120.2W   90 KT 105 MPH
 72H  16/0600Z 16.7N 124.5W   85 KT 100 MPH
 96H  17/0600Z 17.5N 128.5W   75 KT  85 MPH
120H  18/0600Z 18.5N 132.5W   65 KT  75 MPH

$$
Forecaster Blake

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