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HURRICANE GERT DISCUSSION NUMBER  24
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI SEP 17 1999
 
THE LATEST AIR FORCE RESERVE HURRICANE HUNTER FLIGHT REPORTED 149 KT
WINDS AT 868 MB AND 123 KT WINDS AT THE SURFACE ON AN EYEWALL
DROPSONDE. THE MINIMUM CENTRAL PRESSURE WAS 942 MB. SATELLITE
INTENSITY ESTIMATES FROM TAFB...SAB...AND AFWA ARE 127 KT...115
KT...AND 115 KT RESPECTIVELY. BASED ON THE AIRCRAFT DATA...THE
MAXIMUM SUSTAINED WINDS ARE RAISED TO 120 KT. THIS INCREASE IS MOST
LIKELY A MINOR FLUCTUATION AND NOT THE START OF INTENSIFICATION.

GERT IS A LITTLE WEST OF THE PREVIOUS FORECAST TRACK...AND THE
INITIAL MOTION IS NOW ESTIMATED AT 295/09. OTHER THAN THIS... THERE
IS LITTLE CHANGE IN THE FORECAST PHILOSOPHY. GERT IS EXPECTED TO
GRADUALLY TURN NORTHWEST AND NORTH-NORTHWEST TOWARD A BREAK IN THE
SUBTROPICAL RIDGE NEAR BERMUDA. AS SEEN IN THE PREVIOUS PACKAGE...
THE AVIATION MODEL BASED GUIDANCE BENDS THE STORM A LITTLE TO THE
LEFT BY THE END OF THE FORECAST PERIOD. THE OFFICIAL FORECAST
IGNORES THIS AND MORE FOLLOWS THE GFDN AND UKMET...WITH A BEND TO
THE RIGHT. THE TRACK IS SHIFTED SOMEWHAT TO THE LEFT OF THE PREVIOUS
TRACK DUE TO THE CURRENT POSITION AND INITIAL MOTION. 

GERT CONTINUES TO HAVE CONVECTIVE TOPS TO -70C SURROUNDING THE
CENTER AND GOOD OUTFLOW IN ALL BUT THE NORTHWEST QUADRANT. INTENSITY
GUIDANCE CONTINUES TO WEAKEN THE SYSTEM...BUT SATELLITE IMAGERY
INDICATES NO OBVIOUS REASON FOR THIS TO HAPPEN. THE UPPER LEVEL
TROUGH NORTHWEST OF GERT MAY CAUSE SOME INCREASED VERTICAL SHEAR BY
72 HOURS...BUT IT IS MORE LIKELY CONCENTRIC EYEWALL CYCLES WILL BE
THE DOMINATING INFLUENCE ON THE INTENSITY DURING THE FORECAST
PERIOD. THE INTENSITY FORECAST REFLECTS THIS...MAINTAINING 115-120
KT WINDS THROUGH 72 HOURS.

MEDIUM RANGE GUIDANCE INDICATES THAT GERT COULD COME UNCOMFORTABLY
CLOSE TO BERMUDA AFTER THIS FORECAST PERIOD. THEREFORE...INTERESTS
IN BERMUDA SHOULD MONITOR THE PROGRESS OF THE HURRICANE OVER THE
WEEKEND.

THE WIND RADII HAVE BEEN ADJUSTED SLIGHTLY BASED ON THE AIRCRAFT
DATA AND PERIPHERAL SHIP REPORTS.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     17/0900Z 19.7N  55.7W   120 KTS
12HR VT     17/1800Z 20.3N  56.9W   120 KTS
24HR VT     18/0600Z 21.4N  58.4W   120 KTS
36HR VT     18/1800Z 22.8N  60.0W   115 KTS
48HR VT     19/0600Z 24.5N  61.5W   115 KTS
72HR VT     20/0600Z 28.5N  63.5W   115 KTS
 

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