ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 02-Oct-2006 08:45:01 UTC