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HURRICANE GERT DISCUSSION NUMBER  39
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON SEP 20 1999
 
AIR FORCE AIRCRAFT FOUND THE CENTRAL PRESSURE OF 948 MB AT 1748Z
WITH MAX FLIGHT LEVEL WIND SPEED OF 105 KNOTS 70 NM NORTHEAST OF THE
CENTER.  HRD HAS SINCE PRODUCED A SURFACE WIND ANALYSIS BASED ON
THAT FLIGHT TRACK.  USING THIS ANALYSIS AND THE 00Z DVORAK
CLASSIFICATIONS...WHICH HAVE CURRENT INTENSITY NUMBERS YIELDING 90
KNOTS...THE CURRENT INTENSITY HAS BEEN REDUCED TO 95 KNOTS.  THE
FORECAST INTENSITIES HAVE BEEN REDUCED ACCORDINGLY.  THE DEEP
CONVECTION ASSOCIATED WITH THE SYSTEM CONTINUES TO DECREASES AND
BECOME MORE ASYMMETRIC...HOWEVER...THE CURRENT IMAGERY SHOWS SOME
REDEVELOPMENT NEAR THE CENTER.  A GRADUAL WEAKENING IS FORECAST
DURING THE NEXT FEW DAYS AS THE HURRICANE ENCOUNTERS SHEAR AND
COOLER SEA SURFACE TEMPERATURES.
 
INITIAL MOTION IS 345/10...SLIGHTLY MORE NORTHWARD AND FASTER THEN
PREVIOUSLY.  THE LATEST AVN RUN AND THE TRACK MODELS DERIVED FROM IT
SHOW A SWITCH TO MORE NORTHWARD FORECAST TRACKS THEN NORTHEASTWARD
AS SHOWN EARLIER.  THE CURRENT OFFICIAL TRACK FORECAST IS LITTLE
CHANGED FROM PREVIOUSLY AS A BLEND OF THE UKMET AND GFDL MODELS. 
THIS FORECAST PLACES THE STORM ABOUT 100 NM EAST OF BERMUDA IN ABOUT
18 HOURS.  MODELS VARY ON THE FORWARD SPEED BEYOND 48 HOURS BUT THE
GENERAL TREND IS TOWARD ACCELERATION AHEAD OF THE TROUGH.
 
GROSS
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/0300Z 29.6N  62.8W    95 KTS
12HR VT     21/1200Z 31.0N  63.2W    90 KTS
24HR VT     22/0000Z 33.0N  62.8W    85 KTS
36HR VT     22/1200Z 36.0N  61.2W    80 KTS
48HR VT     23/0000Z 40.0N  57.8W    75 KTS
72HR VT     24/0000Z 50.0N  46.0W    65 KTS
 
 
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