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HURRICANE FLOYD DISCUSSION NUMBER  15
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SAT SEP 11 1999
 
THE LATEST REPORT RELAYED FROM THE AIR FORCE HURRICANE HUNTER
AIRCRAFT INDICATES THAT THE PRESSURE HAS CONTINUED TO FALL THIS
MORNING AND THE MINIMUM CENTRAL PRESSURE IS NOW 963 MB...A 31 MB
DROP DURING THE LAST 24 HRS.  THEY ALSO REPORTED A 25 NMI CIRCULAR
EYE...OPEN TO THE SOUTH.  MAXIMUM FLIGHT-LEVEL WINDS OF 107 KTS
WERE RECORDED IN THE NORTHEAST QUADRANT.  THUS...THE INITIAL
INTENSITY IS RAISED TO 90 KTS FOR THIS ADVISORY.  THE OVERALL CLOUD
PATTERN ASSOCIATED WITH FLOYD REMAINS HEALTHY WITH VERY DEEP
CONVECTION PERSISTING AROUND THE CENTER...TOPS TO -70 TO -80C.
HOWEVER...THE OUTFLOW IS BEING DISRUPTED SOMEWHAT OVER THE SOUTHERN
SEMICIRCLE OF THE HURRICANE BY THE UPPER-LEVEL HIGH OVER THE EASTERN
CARIBBEAN.  THE HURRICANE WILL BE MOVING THROUGH THE MID TO UPPER-
LEVEL TROUGH...SEEN IN WATER VAPOR IMAGERY TO THE WEST OF THE
CYCLONE...DURING THE NEXT 24-36 HRS. THIS COUPLED WITH NORTHWESTERLY
SHEAR...DEPICTED IN THE AVIATION MODEL AND REFLECTED IN THE SHIPS
INTENSITY FORECAST...WILL LIKELY CAUSE SOME FLUCTUATIONS IN
INTENSITY THROUGH 36 HRS.  THEREAFTER...CONDITIONS SHOULD BECOME
FAVORABLE FOR ADDITIONAL STRENGTHENING.  THE OFFICIAL FORECAST
BRINGS FLOYD TO MAJOR HURRICANE STATUS BY 72 HRS. 

THE INITIAL MOTION ESTIMATE IS 310/09 KTS. THE FUTURE MOTION OF
FLOYD WILL DEPEND LARGELY ON THE DEVELOPMENT OF A MID-TROPOSPHERIC
RIDGE OVER THE WESTERN ATLANTIC DURING THE NEXT SEVERAL DAYS. THE
MID-LEVEL TROUGH CURRENTLY OVER THE EASTERN U.S. WILL LIFT OUT
DURING THE NEXT 24-36 HRS WITH THE NCEP GLOBAL MODEL SHOWING A
RIDGE BUILDING WESTWARD INTO THE SOUTHEASTERN U.S. BY 48 HRS.
ALL OF THE DYNAMIC-BASED TRACK GUIDANCE REMAINS TIGHTLY CLUSTERED 
ON A WEST-NORTHWEST MOTION BETWEEN 24 AND 48 HRS WITH A MORE
WESTWARD HEADING THEREAFTER. THE UKMET REMAINS THE MOST AGGRESSIVE
MODEL WITH REGARDS TO THE WESTWARD MOTION. THE OFFICIAL FORECAST
TRACK BENDS FLOYD BACK TO A GENERAL WEST-NORTHWEST HEADING AFTER 
12 HRS...WITH A GRADUAL TURN TO THE WEST BY 48 HR.  THIS TRACK IS
VERY SIMILAR TO THE PREVIOUS ADVISORY.
 
BEYOND 72 HRS...THE FORECAST UNCERTAINTY INCREASES CONSIDERABLY
AS THE NEXT MID-LEVEL TROUGH APPROACHES THE EASTERN U.S. AND
WEAKENS THE RIDGE. THE UKMET MODEL TURNS THE HURRICANE BACK TO
THE NORTHWEST JUST OFF THE FLORIDA COAST IN FOUR DAYS AND ENDS UP
OFF THE GEORGIA COAST IN FIVE DAYS. NOGAPS IS SIMILAR ALTHOUGH IT
MAKES THE TURN BACK TO THE NORTHWEST EAST OF THE NORTHERN BAHAMAS.
ALL INTERESTS ALONG THE U.S. EAST COAST SHOULD CONTINUE TO CLOSELY
MONITOR THE PROGRESS OF FLOYD DURING THE NEXT SEVERAL DAYS.
 
GUINEY
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     11/0900Z 21.7N  61.6W    90 KTS
12HR VT     11/1800Z 22.4N  62.7W    90 KTS
24HR VT     12/0600Z 23.3N  64.4W    90 KTS
36HR VT     12/1800Z 24.0N  66.5W    90 KTS
48HR VT     13/0600Z 24.5N  69.0W    95 KTS
72HR VT     14/0600Z 25.0N  74.0W   105 KTS

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