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Hurricane GUILLERMO Forecast Discussion

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WTPZ44 KNHC 011432

800 AM PDT SAT AUG 01 2015

The cloud pattern is not as impressive as it was yesterday when
there was a hint of an eye on satellite imagery. However, Dvorak
T-numbers from all agencies still support an initial intensity of 90
kt. It appears that Guillermo has already peaked in intensity, and
the hurricane is heading toward an environment no longer favorable
for strengthening. On this basis, the NHC forecast calls for a
steady state during the next 12 hours or so, and a gradual weakening
thereafter. By the time Guillermo approaches the Hawaiian
Islands, the upper-level winds are forecast to be even more
unfavorable, and by then, Guillermo is expected to have weakened to
a tropical storm. The NHC forecast is very close to the intensity
consensus model ICON.

The steering currents have begun to weaken, and Guillermo is slowing
down. The best estimate of the initial motion is toward the west or
280 degrees at 12 kt.  The hurricane is already located on the
southwestern edge of the subtropical ridge, and there is a large
weakness of the ridge to its northwest. This pattern should force
the cyclone to slow down even further and turn more to the
west-northwest. The GFS insists on a more northwesterly component
bringing the center of Guillermo north of the Hawaiian Islands. The
ECMWF, on the other hand, brings the cyclone south or near the
Islands.  The NHC forecast is very similar to the previous one,
and is basically on top of the consensus of the ECMWF and the GFS

Due to uncertainties in longer-range track predictions, it is
important for users not to focus on the exact track forecasts at 96
and 120 hours. Given the large spread of the models beyond 72
hours in this case, the forecast uncertainty is particularly high at
those time periods.


INIT  01/1500Z 13.5N 139.0W   90 KT 105 MPH
 12H  02/0000Z 13.9N 141.0W   90 KT 105 MPH
 24H  02/1200Z 14.5N 143.0W   85 KT 100 MPH
 36H  03/0000Z 15.3N 144.7W   80 KT  90 MPH
 48H  03/1200Z 16.2N 146.0W   70 KT  80 MPH
 72H  04/1200Z 17.5N 148.5W   60 KT  70 MPH
 96H  05/1200Z 19.0N 151.5W   50 KT  60 MPH
120H  06/1200Z 20.7N 155.0W   40 KT  45 MPH

Forecaster Avila

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Page last modified: Saturday, 01-Aug-2015 14:33:04 UTC