000 WTNT44 KNHC 281459 TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 30 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1000 AM CDT TUE AUG 28 2012 REPORTS FROM AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT INDICATE THE CENTRAL PRESSURE HAS DECREASED TO ABOUT 976 MB SINCE THE PREVIOUS ADVISORY...BUT IT HAS LEVELED OFF OVER THE PAST FEW HOURS. THE MAXIMUM 850 MB FLIGHT-LEVEL WIND OBSERVED HAS BEEN 89 KT... WHICH EQUATES TO A SURFACE WIND OF ABOUT 71 KT. HOWEVER... BIAS-ADJUSTED SFMR SURFACE WINDS HAVE ONLY BEEN AROUND 60-62 KT... WHICH CORRELATES WELL WITH DROPSONDE BOUNDARY LAYER-DERIVED SURFACE WINDS. AS SUCH...THE INTENSITY OF ISAAC IS BEING MAINTAINED AT 60 KT...WHICH IS JUST BELOW HURRICANE STATUS. CENTER FIXES FROM THE AIRCRAFT INDICATE THAT ISAAC HAS BEEN WOBBLING IN A GENERAL NORTHWESTWARD MOTION OF 310/09 KT. THERE REMAINS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. ISAAC IS FORECAST TO MOVE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE NEAR THE NORTH-CENTRAL GULF COAST OVER THE NEXT 24-36 HOURS... ACCOMPANIED BY A GRADUAL DECREASE IN THE FORWARD SPEED. AS THE RIDGE BUILDS BACK IN TO THE NORTH OF THE CYCLONE...ISAAC IS EXPECTED TO TURN A LITTLE MORE TOWARD THE WEST-NORTHWEST BEFORE IT TURNS NORTHWARD ON DAY 4...AND MOVES NORTHEASTWARD INTO THE OHIO VALLEY REGION ON DAY 5. THE OFFICIAL FORECAST TRACK HAS BEEN NUDGED A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY TRACK AND LIES JUST TO THE RIGHT OF THE CONSENSUS MODELS TV15 AND TCVA. MID-LEVEL DRY AIR ENTRAINMENT CONTINUES TO PLAGUE ISAAC. AS SOON AS THE CYCLONE DEVELOPS INNER-CORE CONVECTION AND THE APPEARANCE OF AN EYE IN RADAR AND SATELLITE IMAGERY...THE CONVECTION ERODES DUE TO THE DRY AIR. DESPITE THE FAVORABLE OCEANIC CONDITIONS AND UPPER-LEVEL OUTFLOW REGIME...ISAAC ONLY HAS ABOUT 12-18 HOURS FOR FURTHER STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...WITH ONLY TIMING ADJUSTMENTS MADE TO THE INTENSITY FORECAST...AND CLOSELY FOLLOWS THE INTENSITY MODEL CONSENSUS. 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 28/1500Z 28.1N 88.5W 60 KT 70 MPH 12H 29/0000Z 28.8N 89.4W 70 KT 80 MPH 24H 29/1200Z 29.7N 90.4W 65 KT 75 MPH...INLAND 36H 30/0000Z 30.5N 91.5W 45 KT 50 MPH...INLAND 48H 30/1200Z 32.0N 92.0W 35 KT 40 MPH...INLAND 72H 31/1200Z 35.0N 92.5W 20 KT 25 MPH...INLAND 96H 01/1200Z 38.5N 90.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 02/1200Z 41.0N 86.0W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER STEWART