Hurricane ISAAC

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HURRICANE ISAAC DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092006
500 AM EDT MON OCT 02 2006
 
HURRICANE ISAAC IS PERSISTENTLY MAINTAINING A COHERENT CENTRAL DENSE
OVERCAST WITH QUITE COLD CLOUD TOPS FOR A HIGH LATITUDE CYCLONE.  
MICROWAVE IMAGERY AT 0002Z AND 0135Z SHOWED THAT ISAAC'S LOW-LEVEL
CENTER WAS DISPLACED ABOUT 30 NMI SOUTHWEST OF THE MID-LEVEL
CENTER.  DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB HAVE
DECREASED TO T4.0 AND T3.5 RESPECTIVELY.  HOWEVER...THE INCREASED
FORWARD SPEED OF ISAAC AS WELL AS THE HIGH ENVIRONMENTAL SURFACE
PRESSURES AS MEASURED BY BUOYS IN THE EASTERN PERIPHERY OF THE
CYCLONE SUGGEST THAT HURRICANE FORCE INTENSITY IS STILL
POSSIBLE...AT LEAST TEMPORARILY.  ISAAC SHOULD BE UNDERGOING
EXTRATROPICAL TRANSITION IN THE NEXT 6 TO 12 HR AS IT MOVES INTO AN
INCREASINGLY BAROCLINIC ENVIRONMENT. THE MAIN QUESTION IS HOW LONG
WILL THE CYCLONE MAINTAIN A SEPARATE IDENTITY.  THE GFS AND UKMET
MODELS SUGGEST ABSORPTION WITHIN A DAY INTO THE DEVELOPING
EXTRATROPICAL LOW TO THE NORTHWEST OF ISAAC.  NOGAPS...IN
CONTRAST...MAINTAINS ISAAC AS THE DOMINANT LOW FOR THE NEXT FEW
DAYS.  THE ECMWF SPLITS THE DIFFERENCE WITH ABSORPTION OF ISAAC IN
ABOUT TWO DAYS AND THIS SCENARIO IS FOLLOWED IN THIS FORECAST WITH
ISAAC'S WINDS GRADUALLY WEAKENING BEFORE THE CYCLONE IS ABSORBED.

ISAAC IS ACCELERATING OFF TO THE NORTH-NORTHEAST AT ABOUT 26
KT...THOUGH THE INITIAL POSITION AND TRANSLATIONAL VELOCITY HAVE A
MODERATE AMOUNT OF UNCERTAINTY.  THE CYCLONE IS EMBEDDED IN THE
SOUTHWESTERLY FLOW BETWEEN A DEEP-LAYERED RIDGE TO ITS SOUTHEAST
AND AN UNSEASONABLY STRONG TROUGH TO ITS WEST.  ISAAC SHOULD
CONTINUE TO ACCELERATE IN THE SAME DIRECTION FOR THE NEXT DAY
BEFORE SLOWING DOWN DURING THE ABSORPTION PROCESS.  THE TRACK
FORECAST FOLLOWS CLOSELY THE RELIABLE MODEL CONSENSUS AND IS
SIMILAR TO...BUT SLIGHTLY FASTER THAN...THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0900Z 40.5N  58.2W    65 KT
 12HR VT     02/1800Z 45.0N  55.1W    60 KT...EXTRATROPICAL
 24HR VT     03/0600Z 49.7N  50.5W    55 KT...EXTRATROPICAL
 36HR VT     03/1800Z 52.1N  46.3W    45 KT...EXTRATROPICAL
 48HR VT     04/0600Z...ABSORBED BY AN EXTRATROPICAL LOW
 
$$
FORECASTER LANDSEA/STEWART
 
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