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000
WTPZ44 KNHC 011432
TCDEP4

HURRICANE GUILLERMO DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL EP092015
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 models.

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.



FORECAST POSITIONS AND MAX WINDS

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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