000 WTNT44 KNHC 280255 TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1000 PM CDT MON AUG 27 2012 THE SATELLITE PRESENTATION OF ISAAC HAS NOT CHANGED VERY MUCH DURING THE PAST FEW HOURS. INFRARED AND MICROWAVE IMAGERY SHOW A STRONG BAND OF CONVECTION...PERHAPS THE BEGINNING OF AN EYEWALL...WRAPPING AROUND THE SOUTH AND EAST PORTIONS OF THE CIRCULATION. HOWEVER... AIRCRAFT OBSERVATIONS INDICATE THAT THE CONVECTIVE BAND WAS OPEN TO THE NORTHWEST AND THAT THE LOW-LEVEL CENTER WAS DISPLACED A LITTLE TO THE SOUTH OF THE ROTATION SEEN IN SATELLITE PICTURES. THE MINIMUM PRESSURE HAS NOT FALLEN SIGNIFICANTLY DURING THE PAST SEVERAL HOURS AND THE NOAA AND AIR FORCE AIRCRAFT HAVE NOT REPORTED WINDS ANY HIGHER THAN WHAT WAS MEASURED LATE THIS AFTERNOON. THEREFORE...ISAAC REMAINS A 60-KT TROPICAL STORM FOR THIS ADVISORY. ISAAC CONTINUES TO HAVE DIFFICULTLY MAINTAINING DEEP CONVECTION OVER THE NORTHERN SEMICIRCLE LIKELY DUE TO SOME DRY AIR ENTRAINMENT. OTHERWISE...ENVIRONMENTAL CONDITIONS SHOULD BE CONDUCIVE FOR STRENGTHENING UNTIL LANDFALL. ISAAC IS FORECAST TO BECOME A HURRICANE OVERNIGHT AND NHC INTENSITY FORECAST IS SLIGHTLY HIGHER THAN MOST OF THE GUIDANCE. ISAAC HAS BEEN MOVING NORTHWESTWARD OR 310 DEGREES AT 9 KT. THE TRACK GUIDANCE HAS CONTINUED TO COME INTO BETTER AGREEMENT DURING THE FIRST 36 TO 48 HOURS OF THE FORECAST PERIOD. ISAAC SHOULD MOVE NORTHWESTWARD TOWARD THE NORTH-CENTRAL GULF COAST WHERE A BREAK IN THE SUBTROPICAL RIDGE IS LOCATED. AS A MID-LATITUDE TROUGH BYPASSES ISAAC IN A DAY OR SO...SOME RIDGING BUILDS TO THE NORTHWEST OF THE CYCLONE. THIS IS EXPECTED TO CAUSE ISAAC TO SLOW DOWN AS IT MOVES INLAND. AFTER 72 HOURS...THE CYCLONE SHOULD BEGIN TO MOVE A LITTLE FASTER TOWARD THE NORTH AND NORTHEAST AS IT MOVES AROUND THE WESTERN SIDE OF A MID-LEVEL RIDGE THAT SLIDES EASTWARD ACROSS THE OHIO VALLEY AND MID-ATLANTIC REGIONS. THE NEW NHC TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND REMAINS BETWEEN THE ECMWF AND GFS MODELS. 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. 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 28/0300Z 27.1N 87.0W 60 KT 70 MPH 12H 28/1200Z 28.0N 88.0W 70 KT 80 MPH 24H 29/0000Z 29.1N 89.2W 80 KT 90 MPH...ON THE COAST 36H 29/1200Z 29.9N 90.1W 65 KT 75 MPH...INLAND 48H 30/0000Z 30.7N 90.7W 50 KT 60 MPH...INLAND 72H 31/0000Z 33.3N 91.7W 30 KT 35 MPH...INLAND 96H 01/0000Z 37.5N 91.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 02/0000Z 40.5N 87.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER BROWN/BLAKE