Caribbean-On-Line's Caribbean Hurricane Blog



TROPICAL STORM GUSTAV DISCUSSION NUMBER 18

Published on August 29, 2008 7:36 AM | Comments

Gustav is looking tricky - the track could still go almost anywhere - and the NHC is expecting to strengthen rapidly into a hurricane:

TROPICAL STORM GUSTAV DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008 500 AM EDT FRI AUG 29 2008

SATELLITE IMAGES SHOW THAT GUSTAV HAS AN EXPANDING CLOUD SHIELD AND IMPRESSIVE BANDING FEATURES. AN AIR FORCE RECONNAISSANCE PLANE THAT HAS BEEN SAMPLING THE STORM'S CIRCULATION FOUND THAT THE SIZE OF GUSTAV HAS SIGNIFICANTLY INCREASED. ALTHOUGH THEY HAVE BEEN UNABLE TO SAMPLE THE CENTER...PEAK FLIGHT LEVEL WINDS OF 52 KT WERE OBSERVED...ALONG WITH SIMILAR VALUES FOR THE SFMR. THE INITIAL INTENSITY REMAINS 55 KT.

THE BEST ESTIMATE OF INITIAL MOTION IS 285/7. THERE IS A COMPLICATED EVOLUTION TO THE STEERING CURRENTS AROUND GUSTAV DURING THE FORECAST PERIOD. THE MID-LEVEL RIDGE OVER FLORIDA THAT HAS BEEN STEERING THE STORM WESTWARD IS FORECAST TO WEAKEN TODAY. THE BERMUDA HIGH IS THEN EXPECTED TO BUILD IN FROM THE WESTERN ATLANTIC AND CAUSE GUSTAV TO MOVE MORE TOWARD THE NORTHWEST OVER THE WEEKEND. ONE BIG QUESTION IS THE EVOLUTION OF A MID- TO UPPER- LEVEL LOW OVER THE SOUTHEASTERN UNITED STATES. SOME OF THE MODELS...SUCH AS THE GFS/GFDL/HWRF...ARE SHOWING THIS LOW CREATING ENOUGH OF A WEAKNESS IN THE BERMUDA HIGH TO ALLOW A MOTION MORE TOWARD THE NORTH-NORTHWEST AS THE SYSTEM CROSSES CUBA. IT WOULD NOT BE SURPRISING IF THAT TRACK BRIEFLY OCCURRED...BUT IN THE LONGER-TERM...A HIGH OVER THE OHIO VALLEY IS EXPECTED TO CAUSE GUSTAV TO GRADUALLY BEND TO THE LEFT. HOWEVER...THERE IS A LARGE UNCERTAINTY IN THE TIMING AND SHARPNESS OF THE BEND. THE UKMET AND GFS HAVE HAD LARGE CHANGES TO THEIR FORECAST FROM THE PREVIOUS RUNS...AND GIVEN THE INCREASING MODEL SPREAD...WE'VE OPTED TO KEEP THE FORECAST SIMILAR TO THE PREVIOUS ONE. HOPEFULLY A G-IV MISSION LATER TODAY WILL HELP RESOLVE SOME OF THESE DIFFERENCES.

AFTER THE STORM MOVES AWAY FROM JAMAICA...SIGNIFICANT INTENSIFICATION IS POSSIBLE. VERTICAL WIND SHEAR IS FORECAST TO BE VERY LIGHT DURING THE NEXT COUPLE OF DAYS...AND COMBINED WITH THE DEEP WARM CARIBBEAN WATERS...COULD PRODUCE A STRONG HURRICANE VERY QUICKLY. THE OFFICIAL FORECAST WILL SHOW RAPID INTENSIFICATION BEFORE IT REACHES WESTERN CUBA AND COULD BE CONSERVATIVE AS SOME MODELS SHOW CATEGORY FOUR STRENGTH AT THAT TIME. A LARGE TROUGH CURRENTLY SEEN IN WATER VAPOR IMAGES OVER THE CENTRAL GULF OF MEXICO IS EXPECTED TO MOVE WESTWARD SLOWLY DURING THE NEXT DAY OR TWO. THIS TROUGH MAY IMPART SOME SOUTHWESTERLY SHEAR ON GUSTAV AS IT ENTERS THE CENTRAL GULF OF MEXICO. ALTHOUGH THE FORECAST SHOWS SOME WEAKENING DUE TO THE SHEAR...GUSTAV IS EXPECTED TO BE A LARGE POWERFUL HURRICANE AS IT APPROACHES THE NORTHERN GULF COAST.



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