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Hurricane IGNACIO Forecast Discussion


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000
WTPZ42 KNHC 271445
TCDEP2

HURRICANE IGNACIO DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP122015
800 AM PDT THU AUG 27 2015

Ignacio continues to produce cloud tops colder than -80C near the
center.  A recent GPM over pass showed a 20-25 n mi wide eye
forming under the overcast.  However, the eye is ragged, and the
deep convection in the eyewall is mainly southwest of the center.
Satellite intensity estimates from TAFB and SAB are 90 kt and 77 kt,
and the CIMSS Advanced Dvorak Technique is estimating 80 kt.  Based
on these data, the initial intensity is increased to 80 kt.

The initial motion is now 285/11.  There is little change in the
forecast philosophy since the previous advisory, with the
subtropical ridge north of Ignacio expected to steer the cyclone
generally west-northwestward through the forecast period with a
gradual decrease in forward speed.  Some spread in the track
guidance develops by day 5, as the ECMWF turns a weaker Ignacio
westward while the GFS turns a stronger Ignacio northwestward.
Despite this, the consensus models and the center of the guidance
envelope are near the previous forecast, and the new forecast is a
slightly faster update of the previous forecast.

Ignacio should remain over warm sea surface temperatures and in an
environment of light vertical wind shear for at least the next two
days, which should allow continued strengthening to a major
hurricane.  After that time, the cyclone should encounter increasing
westerly shear and move over slightly cooler water, which should
start a gradual weakening.  The new intensity forecast follows this
scenario and is basically unchanged since the previous advisory.
One note of uncertainty in the intensity forecast is that the GFS
shear at day 5, which is used in the SHIPS and LGEM models, looks
weaker than that forecast by the ECMWF and UKMET models. Should the
latter models verify, Ignacio could weaken faster than currently
forecast.

Ignacio is expected to move into the Central Pacific basin at about
1800Z.  Therefore, this is the last advisory on this system by the
National Hurricane Center.  Subsequent advisories will be issued by
the Central Pacific Hurricane Center in Honolulu, Hawaii.


FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 12.9N 139.5W   80 KT  90 MPH
 12H  28/0000Z 13.6N 141.1W   90 KT 105 MPH
 24H  28/1200Z 14.5N 143.1W   95 KT 110 MPH
 36H  29/0000Z 15.4N 144.8W  100 KT 115 MPH
 48H  29/1200Z 16.1N 146.1W  100 KT 115 MPH
 72H  30/1200Z 17.5N 149.0W   95 KT 110 MPH
 96H  31/1200Z 19.0N 151.5W   85 KT 100 MPH
120H  01/1200Z 20.5N 154.0W   75 KT  85 MPH

$$
Forecaster Beven



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Page last modified: Thursday, 27-Aug-2015 14:45:37 UTC