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Tropical Storm GUILLERMO Forecast Discussion

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WTPZ44 KNHC 301436

800 AM PDT THU JUL 30 2015

Guillermo's convective pattern continues to improve, with a solid
band curving about half way around the center of circulation.
Dvorak classifications were T3.0/45 kt from TAFB and T2.5/35 kt
from SAB, and the initial intensity is therefore set at 40 kt.
This could be somewhat conservative, given that the latest objective
ADTs are around 45 kt.

The environment ahead of Guillermo looks plenty favorable for
continued strengthening.  Upper-level outflow is expanding around
the cyclone, and Guillermo should remain in a light-shear
environment for at least the next 3-4 days.  In addition, sea
surface temperatures are about 29 degrees C, and the atmosphere is
moist and unstable.  Additional strengthening is anticipated during
the next few days, and there remains a 1 in 3 chance of rapid
intensification during the next 24 hours.  Given the favorable
environment, the official intensity forecast is a little above the
intensity consensus for the entire forecast period.  It should be
noted that the HWRF model shows a stronger hurricane than is
indicated in the official forecast, bringing Guillermo to category 2
strength in about 3 days.  Some weakening should occur by days 4 and
5, mainly due to increased shear and lower oceanic heat content.

Guillermo is moving west-northwestward, or 290/11 kt, to the south
of the subtropical ridge.  The global models indicate that a mid-
to upper-level low located about 1000 miles west of southern
California will deepen and amplify during the next few days, which
should produce a break in the subtropical ridge.  The track models
are in good agreement during the first 48 hours, and most of the
spread beyond that time is due to speed differences.  An overall
westward shift in the guidance envelope necessitated an adjustment
to the official track forecast from 48 hours and beyond, and it
lies close to a consensus of the GFS and ECMWF models.


INIT  30/1500Z  9.1N 127.5W   40 KT  45 MPH
 12H  31/0000Z  9.9N 129.5W   55 KT  65 MPH
 24H  31/1200Z 11.0N 132.5W   65 KT  75 MPH
 36H  01/0000Z 12.0N 135.7W   70 KT  80 MPH
 48H  01/1200Z 12.8N 138.6W   80 KT  90 MPH
 72H  02/1200Z 14.6N 142.8W   80 KT  90 MPH
 96H  03/1200Z 16.0N 145.5W   70 KT  80 MPH
120H  04/1200Z 18.0N 148.0W   60 KT  70 MPH

Forecaster Berg

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Page last modified: Thursday, 30-Jul-2015 14:36:44 UTC