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TROPICAL STORM FLOYD DISCUSSION NUMBER  11
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI SEP 10 1999

LATEST OBSERVATIONS BY THE AIR FORCE HURRICANE HUNTERS SHOW A
CENTRAL PRESSURE OF 985 MB WHICH INDICATES THAT FLOYD IS PROBABLY
STRENGTHENING AND WILL LIKELY BE UPGRADED TO A HURRICANE VERY
SOON...ASSUMING THIS IS CORROBORATED BY WIND OBSERVATIONS FROM THE
AIRCRAFT.  THE LAST FIX LOCATION ALSO SHOWS A BIT OF A NORTHWARD
JUMP...INTO A MASS OF DEEP CONVECTION DEPICTED ON SATELLITE IMAGES.
UPPER-LEVEL OUTFLOW CONTINUES TO BE IMPRESSIVE AND STRENGTHENING IS
FORECAST.  FLOYD COULD BE A MAJOR HURRICANE BY THE END OF THE
FORECAST PERIOD.
 
INITIAL MOTION...300/10...IS A LITTLE TO THE RIGHT OF PREVIOUS
ESTIMATES.  A SYNOPTIC SURVEILLANCE MISSION BY THE NOAA JET SHOWS A
SLIGHT WEAKNESS IN THE 500 MB RIDGE TO THE NORTH OF FLOYD AND THIS
HAS LIKELY CONTRIBUTED TO THE DECREASE IN FORWARD SPEED OVER THE
LAST 12 HOURS OR SO...AND TO THE SLIGHT RIGHTWARD CHANGE IN HEADING.

THERE IS AN UNREALISTIC-LOOKING RING OF VORTICITY SURROUNDING FLOYD
IN THE NCEP GLOBAL MODEL INITIALIZATION.  IN THE MODEL SIMULATION...
A NEW VORTEX SPINS UP ALONG THE RING ON THE NORTH SIDE OF STORM AND
MAY HAVE SOME EFFECT ON THE AVN PREDICTED MOVEMENT OF FLOYD...
PERHAPS CARRYING IT TOO FAR TO THE NORTH.  LOOKING AT THE LARGER-
SCALE STEERING MECHANISMS...THE LARGE MID-TROPOSPHERIC TROUGH OVER
THE EASTERN STATES IS LIKELY TO LIFT OUT IN A COUPLE OF DAYS OR SO.
THEREAFTER THE NCEP GLOBAL MODEL SHOWS A RIDGE BUILDING WESTWARD
INTO THE MID-ATLANTIC STATES AROUND THE 72 HOUR TIME FRAME. IF THIS
VERIFIES...THEN A MORE WESTWARD COMPONENT OF MOTION WOULD DEVELOP
NEAR THE END OF THE FORECAST PERIOD.  THIS IS WHAT IS BEING DEPICTED
BY RECENT RUNS OF THE GFDL MODEL...WHICH TURN FLOYD SHARPLY TOWARD
THE WEST AFTER 48 HOURS.  THE OFFICIAL FORECAST DOES SHOW A LEFTWARD
BEND NEAR THE END OF THE PERIOD...NOT AS DRAMATIC AS THE GFDL BUT
SIMILAR TO THE U.K. MET. OFFICE MODEL WHICH HAS BEEN AN EXCELLENT
PERFORMER IN RECENT YEARS.

PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     10/0900Z 18.9N  58.7W    60 KTS
12HR VT     10/1800Z 19.7N  60.2W    70 KTS
24HR VT     11/0600Z 20.6N  61.8W    75 KTS
36HR VT     11/1800Z 21.7N  63.6W    80 KTS
48HR VT     12/0600Z 22.5N  65.5W    85 KTS
72HR VT     13/0600Z 23.5N  69.0W   100 KTS
 
 
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