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Tropical Storm GUILLERMO Forecast Discussion

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WTPZ44 KNHC 310247

800 PM PDT THU JUL 30 2015

Microwave and conventional satellite imagery indicate that
Guillermo is continuing to become better organized.  The microwave
imagery shows a developing eye, which has occasionally appeared in
visible and infrared imagery.  Satellite intensity estimates are
55 kt from TAFB and SAB, and the latest intensity estimate from
the CIMSS Advanced Dvorak Technique is 65 kt.  Based on these, the
initial intensity is increased to 60 kt.

Guillermo has turned to the right during the past several hours
with the initial motion now 305/12.  Other than that, there is
little change in the forecast philosophy.  The subtropical ridge
north of the storm is forecast to strengthen slightly, causing
Guillermo to accelerate west-northwestward during the next 36
hours. After that time, a mid- to upper-level low well west of
California is expected to produce a break in the ridge, which should
cause the cyclone to slow down and turn more northward by day 5.
The forecast track from 0 to 72 hours has been adjusted northward
based on the initial position and motion.  After 72 hours, the
forecast guidance has again shifted to the left or west, and the
forecast track has also been moved in that direction.  However,
this part of the forecast lies to the north of the various
consensus models.

The developing eye seen in microwave imagery shows that the
structure of Guillermo is conducive for additional rapid
intensification.  Also, the Rapid Intensification Index of the SHIPS
model shows a 50 percent chance of a 30 kt increase in intensity
during the next 24 hours.  Based on this, the intensities during the
first 48 hours of the forecast have been increased over those of the
previous advisory, and this part of the forecast lies near the upper
edge of the intensity guidance. After 48 hours, the cyclone will
move over decreasing sea surface temperatures and possibly encounter
westerly vertical wind shear.  This combination is expected to
cause the cyclone to weaken below hurricane strength by 120 hours.
It should be noted that the early part of the intensity forecast is
of low confidence due to the uncertainties associated with rapid
intensification, and the later part is of low confidence due to
uncertainties in how much shear Guillermo will encounter.


INIT  31/0300Z 10.8N 129.3W   60 KT  70 MPH
 12H  31/1200Z 11.4N 131.4W   70 KT  80 MPH
 24H  01/0000Z 12.3N 134.5W   80 KT  90 MPH
 36H  01/1200Z 13.1N 137.5W   90 KT 105 MPH
 48H  02/0000Z 13.9N 139.8W   95 KT 110 MPH
 72H  03/0000Z 15.5N 143.5W   85 KT 100 MPH
 96H  04/0000Z 16.5N 146.5W   70 KT  80 MPH
120H  05/0000Z 18.0N 149.5W   55 KT  65 MPH

Forecaster Beven

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Page last modified: Friday, 31-Jul-2015 02:47:27 UTC