Hurricane Gustav: Forecast Discussion #6

HURRICANE GUSTAV DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008
1100 AM EDT TUE AUG 26 2008

AN AIR FORCE RECONNAISSANCE MISSION EARLY THIS MORNING FOUND PEAK
FLIGHT-LEVEL WINDS OF 91 KT...AND AN SFMR SURFACE WIND OF 78 KT.
THESE MEASUREMENTS SUPPORT AN INITIAL INTENSITY OF 80 KT. A
DROPSONDE RELEASED IN THE EYE OF GUSTAV DURING THE LAST AIRCRAFT
PASS THROUGH THE CENTER JUST BEFORE 1200 UTC...FOUND A SURFACE
PRESSURE OF 982 MB...BUT WITH 12 KT OF WIND AT THE SURFACE...SO THE
MINIMUM PRESSURE HAS BEEN ESTIMATED SLIGHTLY LOWER. THE AIRCRAFT
AND EARLIER MICROWAVE SATELLITE IMAGERY INDICATE THE PRESENCE OF A
VERY SMALL EYE...HOWEVER THE EYE HAS NOT YET BECOME APPARENT IN
CONVENTIONAL SATELLITE IMAGERY.

GUSTAV CONTINUES TO MOVE NORTHWESTWARD TOWARD THE SOUTHERN COAST OF
HAITI...WITH AN INITIAL MOTION ESTIMATE OF 325/8. TRACK MODEL
GUIDANCE IS IN GOOD AGREEMENT ON A TURN TOWARD THE WEST-NORTHWEST
VERY SOON AROUND THE SOUTH SIDE OF A MID- TO UPPER-LEVEL RIDGE
LOCATED OVER FLORIDA. THERE REMAINS A LARGE AMOUNT OF SPREAD IN
THE MODELS AT 72 HOURS AND BEYOND. THE 00Z UKMET AND ECMWF MODELS
MAINTAIN THE RIDGE OVER THE GULF OF MEXICO...WHICH KEEPS GUSTAVE
MOVING WESTWARD TOWARDS THE YUCATAN PENINSULA. THE
GFDL...HWRF...AND GFS WEAKEN THE RIDGE WHICH ALLOWS FOR A
WEST-NORTHWESTWARD MOTION INTO THE CENTRAL GULF OF MEXICO. THE NEW
NHC TRACK FORECAST LEANS TOWARD THE GFS/HWRF SCENARIO AND IS A
LITTLE TO THE RIGHT OF THE MODEL CONSENSUS.

CONDITIONS APPEAR FAVORABLE FOR ADDITIONAL STRENGTHENING BEFORE THE
CENTER REACHES MOUNTAINOUS TERRAIN ALONG THE SOUTHERN COAST OF
HAITI. SOME WEAKENING IS FORECAST DURING GUSTAV'S PASSAGE OVER
LAND...AND SINCE IT IS A VERY SMALL SYSTEM IT COULD WEAKEN A LITTLE
MORE THAN SHOWN BELOW. THEREAFTER...GUSTAV IS EXPECTED TO BE OVER
WARM WATERS AND IN A LOW SHEAR ENVIRONMENT...WHICH FAVORS
STRENGTHENING. THE OFFICIAL FORECAST IS BELOW THAT OF THE GFDL...
BUT IS CLOSE TO THE INTENSITY CONSENSUS AND THE HWRF.

ONE SHOULD REMEMBER THAT 4 AND 5 DAY FORECASTS ARE SUBJECT TO
POTENTIALLY LARGE ERRORS IN BOTH LOCATION AND INTENSITY.

FORECAST POSITIONS AND MAX WINDS

INITIAL 26/1500Z 17.9N 72.4W 80 KT
12HR VT 27/0000Z 18.6N 73.3W 75 KT
24HR VT 27/1200Z 19.1N 74.6W 80 KT
36HR VT 28/0000Z 19.3N 75.9W 85 KT
48HR VT 28/1200Z 19.4N 77.3W 90 KT
72HR VT 29/1200Z 19.9N 80.2W 100 KT
96HR VT 30/1200Z 21.5N 83.5W 105 KT
120HR VT 31/1200Z 24.0N 87.0W 105 KT


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