000 WTNT44 KNHC 291451 TCDAT4 HURRICANE ISAAC DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1000 AM CDT WED AUG 29 2012 HURRICANE ISAAC IS INLAND OVER SOUTHEASTERN LOUISIANA NEAR HOUMA. THE CYCLONE HAS MAINTAINED AN IMPRESSIVE RADAR SIGNATURE...WHICH INCLUDES A RAGGED 40-NMI DIAMETER EYE. CURVED CONVECTIVE RAINBANDS HAVE INCREASED IN THE EASTERN SEMICIRCLE...AND DOPPLER RADAR VELOCITIES OF NEAR 80 KT OVER WATER SUPPORT KEEPING ISAAC AS A MINIMAL HURRICANE FOR THIS ADVISORY. SIMILAR DOPPLER VELOCITIES OVER LAND AND OVER LAKE PONTCHARTRAIN SUGGEST WIND GUSTS TO NEAR 80 KT COULD OCCUR INLAND OVER SOUTHEASTERN LOUISIANA INTO THIS AFTERNOON. BY LATE THIS AFTERNOON OR EVENING...HOWEVER...ISAAC IS FORECAST TO WEAKEN TO A TROPICAL STORM...AND BECOME A TROPICAL DEPRESSION BY THURSDAY NIGHT. THE INITIAL MOTION ESTIMATE IS 310/5. ISAAC IS EXPECTED TO MOVE SLOWLY NORTHWESTWARD THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE FOR THE NEXT 24 HOURS...AND THEN TURN NORTH-NORTHWESTWARD AND NORTHWARD AROUND THE WESTERN PERIPHERY OF THE RIDGE BY 36 AND 48 HOURS...RESPECTIVELY. BY 72 HOURS...ISAAC IS FORECAST TO BECOME A POST-TROPICAL REMNANT LOW PRESSURE SYSTEM THAT SHOULD MOVE NORTHEASTWARD TO EAST-NORTHEASTWARD WHEN IT WILL BE CAUGHT UP IN WEAK MID-LATITUDE WESTERLIES. THERE ARE CURRENTLY NO INDICATIONS IN ANY OF THE MODEL GUIDANCE SUGGESTING THAT ISAAC WILL TAP INTO ANY BAROCLINIC ENERGY SOURCES THAT COULD RESULT IN EXTRATROPICAL STRENGTHENING OVER THE CENTRAL UNITED STATES. THE OFFICIAL TRACK FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY TRACK AND IS JUST EAST OF THE MODEL CONSENSUS. SINCE ISAAC IS FORECAST TO MOVE SLOWLY OVER THE NEXT 24-36 HOURS... THERE WILL BE A PROLONGED THREAT OF FLOODING FROM HEAVY RAINS OVER THE NORTHERN GULF COAST AREA AND THE SOUTH-CENTRAL UNITED STATES. NATIONAL OCEAN SERVICE TIDE GAGES INDICATE THAT STORM SURGE HEIGHTS OF 6 TO 8 FEET ARE STILL 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 THROUGH TODAY. A SPECIAL THANKS TO THE CREWS OF THE AIR FORCE RESERVE AND NOAA HURRICANE HUNTERS WHO FLEW A TOTAL OF 34 HAZARDOUS MISSIONS INTO ISAAC...WHICH RESULTED IN AN IMPRESSIVE TOTAL OF 95 CENTER FIXES. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 29.6N 90.7W 65 KT 75 MPH...INLAND 12H 30/0000Z 30.2N 91.4W 55 KT 65 MPH...INLAND 24H 30/1200Z 31.2N 92.2W 45 KT 50 MPH...INLAND 36H 31/0000Z 32.8N 93.1W 30 KT 35 MPH...INLAND 48H 31/1200Z 34.6N 93.5W 25 KT 30 MPH...INLAND 72H 01/1200Z 38.0N 92.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/1200Z 40.0N 89.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 03/1200Z 41.0N 85.0W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER STEWART