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TROPICAL STORM HERNAN DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP082014
800 PM PDT SAT JUL 26 2014

Satellite imagery indicates that Hernan has become better organized
this evening.  A central dense overcast has formed with cloud tops
to -75C, and a mid-level eye is present in recent AMSU and SSM/IS
overpasses.  Satellite intensity estimates are 35 kt and 45 kt from
SAB and TAFB.  In addition, the ADT, AMSU, and SATCON techniques
from CIMSS at the University of Wisconsin all estimate an
intensity of 45-50 kt.  The initial intensity is increased to 45 kt,
and this could be a little conservative.  The cirrus outflow is good
to excellent over the northern semicircle and fair to poor
elsewhere.

The initial motion is 320/12, with Hernan being steered along the
southwest side of a strong mid-level ridge centered over the
southern United States.  This pattern is expected to persist, and
it should keep Hernan moving northwestward to west-northwestward
at about the same speed for the next couple of days. After that, a
gradual turn toward the west with a decrease in forward speed is
expected as the weakening cyclone is steered mainly by low-level
flow.  The models have again shifted a little northward, and the
official track forecast is again nudged in that direction.

The forecast track keeps Hernan over sea surface temperatures of
29C for the next 18-24 hours.  This, combined with a light vertical
wind shear environment, should allow continued strengthening during
this time.  Based on current trends, the intensity forecast has
been nudged upward and now shows Hernan near hurricane strength
in 24 hours.  There is a possibility that the cyclone could get
stronger than this, as the Rapid Intensification Index of the SHIPS
model shows a 30 percent chance of 30 kt of strengthening during the
next 24 hours. After 24-36 hours, decreasing sea surface
temperatures and increasing shear should cause Hernan to steadily
weaken.


FORECAST POSITIONS AND MAX WINDS

INIT  27/0300Z 16.2N 108.9W   45 KT  50 MPH
 12H  27/1200Z 17.5N 110.6W   55 KT  65 MPH
 24H  28/0000Z 18.9N 112.8W   60 KT  70 MPH
 36H  28/1200Z 20.2N 115.2W   60 KT  70 MPH
 48H  29/0000Z 21.5N 117.6W   45 KT  50 MPH
 72H  30/0000Z 23.0N 121.5W   30 KT  35 MPH
 96H  31/0000Z 23.5N 125.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  01/0000Z 23.5N 128.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven

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