Hurricane GIL

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HURRICANE GIL DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072013
800 PM PDT WED JUL 31 2013

GIL HAS BEEN RAPIDLY INTENSIFYING FOR THE PAST 24-30 HR.  A SMALL
CENTRAL DENSE OVERCAST HAS FORMED WITH EYEWALL CLOUD TOPS COLDER
THAN -80C...AND THERE ARE RAGGED OUTER BANDS NORTH AND SOUTHEAST OF
THE CDO.  HOWEVER...THE EYE SEEN PREVIOUSLY HAS DISAPPEARED...
SUGGESTING THE POSSIBILITY THAT THE INTENSIFICATION RATE HAS
SLOWED.  SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM TAFB AND 65
KT FROM SAB.  BASED ON THIS...THE INITIAL INTENSITY IS INCREASED TO
70 KT.

THE INITIAL MOTION REMAINS 285/10.  GIL CONTINUES TO BE STEERED BY
THE FLOW SOUTH OF A SUBTROPICAL RIDGE WHICH IS FORECAST TO PERSIST
THROUGH 72 HR. THIS PATTERN WILL KEEP GIL ON A GENERAL WEST-
NORTHWESTWARD TO WESTWARD TRACK.  AFTER THAT...THE GFS AND ECMWF
MODELS SHOW A MID/UPPER-LEVEL TROUGH NORTH OF 20N NEAR 140W THAT
SHOULD WEAKEN THE RIDGE.  THIS SHOULD CAUSE GIL TO SLOW ITS FORWARD
MOTION BY THE END OF THE FORECAST PERIOD.  THE NEW FORECAST TRACK
IS AN UPDATE OF THE PREVIOUS TRACK AND LIES NEAR THE CENTER OF THE
MODEL GUIDANCE ENVELOPE.
 
THE INTENSITY FORECAST HAS TWO COMPLICATING FACTORS.  THE FIRST IS
THAT THE FORECAST TRACK IS ROUGHLY PARALLEL TO THE SEA SURFACE
TEMPERATURE GRADIENT.  A MORE NORTHERLY MOTION...SIMILAR TO THE
GFS...WOULD BRING THE CYCLONE OVER COOLER SSTS AND INTO STRONGER
VERTICAL WIND SHEAR AFTER 24-48 HR.  A MORE SOUTHERLY MOTION...
SIMILAR TO THE FLORIDA STATE SUPERENSEMBLE...WOULD KEEP GIL OVER
WARMER WATER AND IN A LESS HOSTILE SHEAR ENVIRONMENT.  THE SECOND
FACTOR IS UNCERTAINTY AS TO WHETHER THE RAPID INTENSIFICATION IS
OVER OR NOT...WITH THE RAPID INTENSIFICATION INDEX OF THE SHIPS
MODEL SHOWING A DECREASED CHANCE OF CONTINUED RAPID STRENGTHENING. 
THE NEW INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS...
EXCEPT AT 24 HR WHEN THE FORECAST PEAK INTENSITY IS A LITTLE ABOVE
THE GUIDANCE.  AN ALTERNATIVE SCENARIO IS THAT GIL CONTINUES TO
RAPIDLY INTENSIFY FOR 12-24 HR AND GETS SIGNIFICANTLY STRONGER THAN
CURRENTLY FORECAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  01/0300Z 14.2N 121.8W   70 KT  80 MPH
 12H  01/1200Z 14.6N 123.2W   80 KT  90 MPH
 24H  02/0000Z 14.9N 125.3W   85 KT 100 MPH
 36H  02/1200Z 15.2N 127.2W   80 KT  90 MPH
 48H  03/0000Z 15.4N 128.8W   75 KT  85 MPH
 72H  04/0000Z 15.5N 132.0W   65 KT  75 MPH
 96H  05/0000Z 15.5N 135.5W   50 KT  60 MPH
120H  06/0000Z 15.5N 138.5W   40 KT  45 MPH
 
$$
FORECASTER BEVEN
 
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