000 WTNT44 KNHC 282053 TCDAT4 HURRICANE ISAAC DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 400 PM CDT TUE AUG 28 2012 SINCE THE LAST RECON FLIGHTS INTO ISAAC...WHEN A BIAS-CORRECTED SFMR WIND OF 64 KT WAS OBSERVED...THE RADAR AND SATELLITE APPEARANCE HAS CONTINUED TO BECOME BETTER DEFINED. ON THIS BASIS...THE ESTIMATED INTENSITY HAS BEEN INCREASED TO 70 KT. TRENDING THROUGH ALL OF THE WIGGLES AND WOBBLES IN THE AIRCRAFT FIXES YIELDS A GENERAL NORTHWESTWARD MOTION OF 310/07 KT. ISAAC REMAINS ON TRACK...AND THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE EARLY PART OF THE FORECAST. ISSAC IS EXPECTED TO CONTINUE NORTHWESTWARD TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE THAT IS ORIENTED EAST-WEST ALONG 30N LATITUDE. BECAUSE OF THIS WEAKNESS... THE STEERING FLOW IS FORECAST TO DECREASE OVER THE NEXT 36-48 HOURS...WHICH WILL RESULT IN ISAAC SLOWING DOWN SOME MORE. AFTERWARDS...THE RIDGE IS FORECAST TO BUILD BACK IN BY ALL OF THE MODELS...ALBEIT TO VARYING DEGREES...WHICH SHOULD CAUSE THE CYCLONE TO TURN SLIGHTLY TOWARD THE WEST-NORTHWEST BEFORE IT TURNS NORTHWARD BY DAY 4...AND THEN MOVE NORTHEASTWARD INTO THE LOWER GREAT LAKES AND OHIO VALLEY REGIONS BY DAY 5. IN THE LATTER PART OF THE FORECAST PERIOD THE FORECAST HAS BEEN NUDGED A LITTLE TO THE LEFT OF THE PREVIOUS TRACK...BUT REMAINS TO THE RIGHT OF THE CONSENSUS MODELS THAT HAVE RECENTLY HAD A LEFTWARD BIAS. ALTHOUGH NOT EXPLICITLY FORECAST DUE TO LAND INTERACTION AT 12 HOURS...FAVORABLE WATER TEMPERATURES ALONG WITH AN IMPRESSIVE UPPER-LEVEL OUTFLOW REGIME SUGGEST THAT ISAAC COULD STRENGTHEN A LITTLE MORE BEFORE LANDFALL OCCURS. HOWEVER...BECAUSE OF THE UNUSUALLY LARGE WIND FIELD...RAPID INTENSIFICATION IS NOT EXPECTED. ISAAC REMAINS 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 28/2100Z 28.7N 89.2W 70 KT 80 MPH 12H 29/0600Z 29.4N 90.0W 70 KT 80 MPH...INLAND 24H 29/1800Z 30.3N 91.0W 55 KT 65 MPH...INLAND 36H 30/0600Z 31.3N 91.9W 35 KT 40 MPH...INLAND 48H 30/1800Z 33.0N 92.5W 30 KT 35 MPH...INLAND 72H 31/1800Z 36.0N 92.5W 20 KT 25 MPH...INLAND 96H 01/1800Z 39.0N 90.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 02/1800Z 41.5N 86.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER STEWART