000 WTNT44 KNHC 280856 TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 29 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 400 AM CDT TUE AUG 28 2012 REPORTS FROM THE AIR FORCE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CENTRAL PRESSURE HAS DROPPED A LITTLE MORE...BUT SO FAR...THE MAXIMUM FLIGHT-LEVEL AND SFMR-OBSERVED SURFACE WINDS STILL DO NOT QUITE SUPPORT HURRICANE INTENSITY. THE CURRENT INTENSITY IS HELD AT 60 KT PENDING ADDITIONAL OBSERVATIONS FROM THE HURRICANE HUNTERS. ALTHOUGH THE WIND FIELD REMAINS RATHER BROAD AND RELATIVELY FLAT...RECENT AIRCRAFT DATA SUGGEST THAT THE MAXIMUM WINDS ARE NOW OCCURRING SOMEWHAT CLOSER TO THE CENTER OVER THE NORTHERN SEMICIRCLE OF THE CYCLONE. THIS WOULD SUGGEST THAT THE INNER CORE CIRCULATION IS BECOMING BETTER DEFINED...AND STRENGTHENING MIGHT BE IMMINENT. UPPER-LEVEL OUTFLOW IS WELL-ESTABLISHED OVER THE SOUTHERN SEMICIRCLE OF THE SYSTEM...BUT CENTRAL CONVECTION CONTINUES TO FLUCTUATE. THE LATTER IS PRESUMABLY DUE TO A CONTINUED INTRUSION OF DRY AIR INTO THE CORE REGION. THE STATISTICAL-DYNAMICAL GUIDANCE IS A LITTLE LOWER THAN IN PREVIOUS RUNS...AND THE STORM HAS ONLY ABOUT 12-24 HOURS BEFORE MOVING INLAND. THE OFFICIAL INTENSITY FORECAST IS JUST SLIGHTLY LOWER THAN THE PREVIOUS ONE. CENTER FIXES FROM THE AIRCRAFT INDICATE THAT THE STORM HAS WOBBLED ON A GENERALLY WESTWARD COURSE OVER THE PAST FEW HOURS. THIS IS BELIEVED TO BE TEMPORARY...HOWEVER...AND THE LONGER-TERM MOTION ESTIMATE IS ABOUT 305/10. THE CURRENT AND FORECAST STEERING REGIME ARE BASICALLY THE SAME AS IN THE PREVIOUS PACKAGE. ISAAC IS EXPECTED TO MOVE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE NEAR THE NORTH-CENTRAL GULF COAST...WITH SOME SLOWING OF FORWARD SPEED DURING THE NEXT COUPLE OF DAYS AS A RIDGE BUILDS A LITTLE TO THE NORTHWEST OF THE CYCLONE. LATER ON...THE SYSTEM SHOULD TURN NORTHWARD AND NORTHEASTWARD INTO THE OHIO VALLEY REGION AS IT MOVES AROUND THE WESTERN PERIPHERY OF A MID-LEVEL ANTICYCLONE. ISAAC IS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM SURGE...HEAVY RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST. FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT CENTER LOCATION. THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION DURING THE NEXT FEW DAYS. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 27.5N 88.1W 60 KT 70 MPH 12H 28/1800Z 28.5N 89.1W 70 KT 80 MPH 24H 29/0600Z 29.5N 90.1W 75 KT 85 MPH...NEAR THE COAST 36H 29/1800Z 30.3N 90.9W 55 KT 65 MPH...INLAND 48H 30/0600Z 31.4N 91.5W 45 KT 50 MPH...INLAND 72H 31/0600Z 34.5N 92.5W 25 KT 30 MPH...INLAND 96H 01/0600Z 38.0N 91.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0600Z 40.5N 87.0W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH