ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM HURRICANE ISAAC DISCUSSION NUMBER 32 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1000 PM CDT TUE AUG 28 2012 ISAAC PASSED OVER THE MISSISSIPPI RIVER DELTA IN EXTREME SOUTHEAST LOUISIANA AROUND 2345 UTC. SINCE THAT TIME...THE CENTER HAS WOBBLED WESTWARD AND HAS MOVED BACK OVER WATER. A NORTHWESTWARD MOTION HAS RECENTLY RESUMED AND A SECOND LANDFALL SHOULD OCCUR LATER TONIGHT NEAR GRAND ISLE. DATA FROM NOAA AND AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE MINIMUM PRESSURE HAS CONTINUED TO GRADUALLY FALL AND IS NOW 968 MB. THE AIR FORCE RESERVE AIRCRAFT HAS MEASURED A PEAK 850-MB FLIGHT-LEVEL WIND OF 96 KT AND BIAS-CORRECTED SFMR WINDS OF AROUND 65 KT. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 70 KT. LITTLE CHANGE IN STRENGTH IS EXPECTED DURING THE NEXT 12 HOURS OR SO AS THE CENTER MOVES ACROSS THE BAYOUS OF SOUTHEASTERN LOUISIANA. STEADY WEAKENING SHOULD COMMENCE LATER WEDNESDAY AS THE CENTER MOVES FARTHER INLAND. SMOOTHING THROUGH THE WOBBLES DURING THE PAST FEW HOURS...THE LONGER TERM MOTION ESTIMATE IS 310/7 KT. ISAAC IS EXPECTED TO MOVE SLOWLY NORTHWESTWARD DURING THE NEXT 24 TO 36 HOURS AS A MID-LEVEL RIDGE TO THE NORTHWEST OF THE CYCLONE SLIDES EASTWARD. AS THE RIDGE MOVES ACROSS THE OHIO VALLEY AND INTO THE MID-ATLANTIC REGION...THIS SHOULD CAUSE ISAAC TO TURN NORTH-NORTHWESTWARD AND NORTHWARD IN A COUPLE OF DAYS. AFTER THAT TIME...THE CYCLONE IS EXPECTED TO TURN NORTHEASTWARD AS IT ENTERS THE MID-LATITUDE WESTERLY FLOW. THE GLOBAL MODEL GUIDANCE HAS BEEN SHIFTING WESTWARD DURING THE PAST COUPLE OF RUNS...AND THE NHC FORECAST HAS BEEN ADJUSTED IN THAT DIRECTION. BECAUSE OF THE SLOW MOTION OF ISAAC...A PROLONGED PERIOD OF STRONG WINDS AND HEAVY RAINFALL ARE EXPECTED OVER 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. NATIONAL OCEAN SERVICE TIDE GAUGES INDICATE THAT STORM SURGE HEIGHTS OF 6 TO 10 FEET ARE OCCURRING ALONG PORTIONS OF THE COAST OF SOUTHEASTERN LOUISIANA AND MISSISSIPPI. GIVEN THE LONG DURATION OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN HIGH FOR THE NEXT 12 TO 24 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 29.0N 89.7W 70 KT 80 MPH 12H 29/1200Z 29.6N 90.6W 65 KT 75 MPH...INLAND 24H 30/0000Z 30.3N 91.4W 55 KT 65 MPH...INLAND 36H 30/1200Z 31.5N 92.3W 35 KT 40 MPH...INLAND 48H 31/0000Z 33.2N 93.2W 25 KT 30 MPH...INLAND 72H 01/0000Z 37.0N 94.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/0000Z 40.0N 91.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 03/0000Z 41.5N 86.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER BROWN NNNN
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Page last modified: Monday, 31-Dec-2012 12:09:27 UTC