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HURRICANE ISAAC DISCUSSION NUMBER  30
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT THU SEP 28 2000

IT WAS NOTED EARLIER THAT THE ENVIRONMENT APPEARED FAVORABLE...AND 
SATELLITE IMAGES THIS AFTERNOON INDICATE THAT INDEED THERE HAS BEEN
FURTHER STRENGTHENING.  ENHANCED IR DATA SHOWS THAT COLDER CLOUD
TOPS HAVE WRAPPED AROUND THE NORTHERN SIDE OF THE CDO.  THREE- AND
SIX-HOURLY AVERAGED OBJECTIVE T NUMBERS ARE ABOUT 6.2...WHICH
EQUATES TO A 120-KNOT...CAT. 4...CURRENT INTENSITY ESTIMATE.  IT IS
PRESUMED THAT THE SYSTEM IS NEAR MAXIMUM STRENGTH...BUT WE WOULD NOT
BE TOO SURPRISED IF A LITTLE MORE INTENSIFICATION TOOK PLACE.  IT IS
QUITE RARE TO SEE SUCH AN INTENSE HURRICANE APPROACHING 30N
LATITUDE.  BY 48 HOURS THE HURRICANE SHOULD BE MOVING OVER SUB-26
DEG C WATERS...SO SIGNIFICANT WEAKENING IS EXPECTED LATE IN THE
FORECAST PERIOD. 

FORWARD SPEED HAS INCREASED TO 17 KNOTS OR MORE.  ISAAC CONTINUES TO
MOVE AROUND THE WESTERN PERIPHERY OF A DEEP-LAYER ANTICYCLONE. 
NUMERICAL GUIDANCE IS IN GOOD AGREEMENT ON A GRADUAL TURN TO THE
NORTH AND NORTHEAST DURING THE FORECAST PERIOD.  NOT TOO MUCH
ACCELERATION IS SHOWN NEAR THE END OF THE PERIOD SINCE THE GLOBAL
MODEL SHOWS THAT THE 500 MB SHORTWAVE TROUGH MOVING OFF THE
NORTHEAST U.S. COAST TOMORROW WILL BYPASS ISAAC.  HOWEVER IT IS
STILL BELIEVED THAT THE CYCLONE WILL BE MOVED ALONG BY THE MID-
LATITUDE WESTERLIES IN ABOUT 72 HOURS...AND SHOULD BE LOSING
TROPICAL CHARACTERISTICS SOON THEREAFTER.  
 
FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     28/2100Z 27.4N  54.7W   120 KTS
12HR VT     29/0600Z 29.7N  55.8W   120 KTS
24HR VT     29/1800Z 32.7N  56.0W   115 KTS
36HR VT     30/0600Z 35.5N  54.5W   110 KTS
48HR VT     30/1800Z 38.0N  52.0W   100 KTS
72HR VT     01/1800Z 42.5N  46.0W    80 KTS
 
 
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