HOME	PRODUCTS	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM COR
HURRICANE ISAAC DISCUSSION NUMBER  19
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON SEP 25 2000

...CORRECTED ADVISORY NUMBER TO 19... 

ISAAC HAS BEEN ABLE TO REMAIN NEARLY STEADY IN INTENSITY THE PAST 6
HOURS...DESPITE SOME WEAK WESTERLY SHEAR.  THE INITIAL INTENSITY IS
HELD AT 90 KT BASED ON A SATELLITE INTENSITY ESTIMATE OF 90 KT FROM
BOTH TAFB AND KGWC.  ISAAC MAY INTERMITTENTLY BE A LITTLE STRONGER
AS INDICATED BY A SATELLITE INTENSITY ESTIMATE OF 102 KT FROM SAB...
BUT THE EYE FEATURE HAS NOT BEEN ABLE TO PERSIST IN INFRARED IMAGERY
AND THE CDO IS ELONGATED MORE EAST-WEST WHICH SUGGESTS SOME
DISRUPTION OF THE INNER CORE CONVECTION AND WIND FIELD.  HOWEVER...
TRMM AND SSMI OVERPASSES DURING THE PAST 4 HOURS STILL INDICATE A
SMALL EYE ON THE ORDER OF 5 TO 10 NM IN DIAMETER.  OUTFLOW REMAINS
IMPRESSIVE...ESPECIALLY IN THE NORTHERN SEMICIRCLE.
 
MOTION ESTIMATE CONTINUES TO BE...300/9.  THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING.  ISAAC IS
TRACKING AROUND THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE
AND...IN TIME...THE TROUGH OVER THE EASTERN U.S. IS EXPECTED TO
GRADUALLY PUSH OFF THE EAST COAST AND ERODE THE WESTERN PORTION OF
THE SUBTROPICAL RIDGE.  THIS SHOULD ALLOW ISAAC TO GRADUALLY TURN
MORE POLEWARD...POSSIBLY BY THE END OF THE FORECAST PERIOD.  THIS IS
IN AGREEMENT WITH ALL OF THE GLOBAL MODELS AND THE OFFICIAL TRACK IS
CLOSE TO THE GFDL MODEL.
 
THERE IS NO CHANGE TO THE PREVIOUS INTENSITY FORECAST.  THERE WILL
LIKELY BE SOME FLUCTUATIONS IN THE INTENSITY DURING THE NEXT 48
HOURS...BUT LITTLE SIGNIFICANT DEVELOPMENT SHOULD OCCUR FOR THE MOST
PART DUE TO THE WEAK TO MODERATE WESTERLY SHEAR AHEAD OF THE SYSTEM.
 
HOWEVER... AFTER 48 HOURS...ISAAC WILL BE MOVING OVER WARMER WATER
AND THE SHEAR MAY LET UP JUST ENOUGH TO ALLOW FOR SOME STRENGTHENING
BEFORE INCREASING SOUTHWESTERLY SHEAR BEGINS TO AFFECT THE CYCLONE
AHEAD OF THE U.S. EAST COAST UPPER-LEVEL TROUGH.
 
THE 34-KT WIND RADII WERE INCREASED SLIGHTLY BASED ON RECENT GALE
WIND RADIUS ANALYSES FROM KGWC.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     26/0300Z 18.3N  42.3W    90 KTS
12HR VT     26/1200Z 19.0N  43.5W    90 KTS
24HR VT     27/0000Z 20.0N  45.1W    90 KTS
36HR VT     27/1200Z 21.0N  47.0W    90 KTS
48HR VT     28/0000Z 22.5N  49.5W    85 KTS
72HR VT     29/0000Z 25.0N  54.0W    85 KTS
 
 
NNNN