Tropical Storm Gustav: 4 pm CDT Forecast Discussion

TROPICAL STORM GUSTAV DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008
500 PM EDT MON AUG 25 2008

AFTER ITS RATHER RAPID INCREASE IN ORGANIZATION EARLIER TODAY...THE
CLOUD PATTERN ASSOCIATED WITH GUSTAV HAS BECOME A LITTLE
RAGGED-LOOKING...PARTICULARLY NEAR THE CENTER. THE AIR FORCE
HURRICANE HUNTERS REPORTED A VERY SMALL AREA OF STRONG WINDS JUST
TO THE SOUTHEAST OF THE CENTER WITH A PEAK FLIGHT LEVEL WIND SPEED
OF 67 KT. USING A 75 PERCENT RATIO OF SURFACE TO FLIGHT LEVEL
WINDS APPROPRIATE FOR THE 925 MB FLIGHT ALTITUDE GIVES 50 KT FOR
THE INTENSITY ESTIMATE. ASSUMING THE CURRENTLY LESS-ORGANIZED
APPEARANCE OF THE CYCLONE IS MERELY TEMPORARY...STRENGTHENING IS
LIKELY GIVEN THE APPARENTLY FAVORABLE METEOROLOGICAL AND OCEANIC
CONDITIONS. LATER IN THE FORECAST PERIOD...THE STRENGTH OF GUSTAV
WILL OBVIOUSLY BE A STRONG FUNCTION OF HOW MUCH THE CIRCULATION
INTERACTS WITH LAND. INTERESTINGLY...THE GFS CONTINUES TO FAIL TO
SHOW DEVELOPMENT OF THE CYCLONE AND THE U.K. MET OFFICE GLOBAL
MODEL SHOWS WEAKENING.

THE INITIAL MOTION CONTINUES TOWARD THE NORTHWEST...315/12. THE
GLOBAL MODELS DEPICT A MID-TROPOSPHERIC ANTICYCLONE CENTERED NEAR
FLORIDA OVER THE NEXT SEVERAL DAYS. THE STEERING CURRENTS
ASSOCIATED WITH THIS FEATURE SHOULD CAUSE THE MOTION OF GUSTAV TO
GRADUALLY BEND TOWARD THE LEFT AND THIS IS ALSO SHOWN BY THE
OFFICIAL TRACK FORECAST...WHICH IS SLIGHTLY WEST OF THE PREVIOUS
ONE. SOME OF THE TRACK MODELS SUCH AS THE GFDL AND HWRF ARE TO THE
LEFT OF THIS NHC FORECAST. NOTE THAT THERE IS SUBSTANTIAL
UNCERTAINTY IN THE 4 AND 5 DAY FORECAST POSITIONS...AND ONE SHOULD
NOT FOCUS ON THESE PRECISE POINTS.

THE WIND RADII WERE DECREASED A LITTLE SINCE THE AIRCRAFT
OBSERVATIONS SHOWED THAT GUSTAV IS A LITTLE SMALLER THAN EARLIER
ESTIMATED.

FORECAST POSITIONS AND MAX WINDS

INITIAL 25/2100Z 16.3N 71.0W 50 KT
12HR VT 26/0600Z 17.2N 72.0W 60 KT
24HR VT 26/1800Z 18.4N 73.3W 65 KT...INLAND
36HR VT 27/0600Z 19.4N 74.4W 65 KT
48HR VT 27/1800Z 20.2N 75.5W 65 KT...INLAND
72HR VT 28/1800Z 21.3N 77.5W 55 KT...INLAND
96HR VT 29/1800Z 22.0N 79.0W 50 KT...INLAND
120HR VT 30/1800Z 23.0N 81.0W 50 KT...INLAND


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