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#538391 (Received by flhurricane at: 4:59 PM 29.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 400 PM CDT WED AUG 29 2012 ISAAC CONTINUES TO TRUDGE SLOWLY TO THE NORTHWEST ACROSS SOUTHEASTERN LOUISIANA...AND THE INITIAL MOTION REMAINS 310/5 KT...BASED ON DOPPLER RADAR DATA FROM SLIDELL AND FT. POLK LOUISIANA. THE MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE PREVIOUS OFFICIAL TRACK...SO NO SIGNIFICANT CHANGES WERE MADE FOR THIS ADVISORY. ISAAC SHOULD CONTINUE TO MOVE NORTHWESTWARD AND EVENTALLY NORTHWARD THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE OVER THE NEXT 36-48 HOURS. BY DAY 3 WHEN THE REMNANT CYCLONE IS OVER THE UPPER-MIDWEST...ISAAC SHOULD TURN EAST-NORTHEASTWARD WHEN IT INTERACTS WITH WEAK MID-LATITUDE WESTERLY FLOW. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS ADVISORY TRACK...AND LIES BETWEEN THE MODEL CONSENSUS AND THE ECMWF MODEL. STRONG BANDS OF THUNDERSTORMS CONTINUE TO DEVELOP OVER WATER IN THE THE EASTERN SEMICIRCLE AND ALSO SOUTHWEST OF THE CENTER. THEY HAVE OCCASIONALLY PRODUCED SUSTAINED TROPICAL-STORM-FORCE WINDS ALONG WITH GUSTS EXCEEDING 60 KT. THOSE STRONG RAINBANDS WILL GRADUALLY SPREAD WESTWARD TONIGHT ACROSS THE COASTAL AREAS OF SOUTHEASTERN LOUISIANA AND SOUTHERN MISSISSIPPI...INCLUDING THE NEW ORLEANS METROPOLITAN AREA. BY THURSDAY NIGHT...ISAAC COULD WEAKEN TO A TROPICAL DEPRESSION...AND IT SHOULD BECOME A POST-TROPICAL REMNANT LOW PRESSURE SYSTEM BY FRIDAY. THERE REMAINS NO INDICATION IN ANY OF THE NHC MODEL GUIDANCE THAT ISAAC WILL BE ABLE TO ACQUIRE ANY BAROCLINIC ENERGY THAT COULD CAUSE IT TO STRENGTHEN INTO A SIGNIFICANT EXTRATROPICAL LOW WHILE IT IS OVER THE UNITED STATES. SINCE ISAAC WILL CONTINUE 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 NEAR 7 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 TONIGHT. PUBLIC ADVISORY TIMES HAVE REVERTED BACK TO A 3-HOURLY CYCLE. THE NEXT INTERMEDIATE PUBLIC ADVISORY WILL BE ISSUED AT 700 PM CDT/0000Z. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 30.0N 91.1W 60 KT 70 MPH...INLAND 12H 30/0600Z 30.7N 91.7W 50 KT 60 MPH...INLAND 24H 30/1800Z 32.0N 92.6W 40 KT 45 MPH...INLAND 36H 31/0600Z 33.8N 93.3W 30 KT 35 MPH...INLAND 48H 31/1800Z 35.7N 93.4W 25 KT 30 MPH...INLAND 72H 01/1800Z 38.6N 91.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/1800Z 40.0N 88.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 03/1800Z 40.5N 83.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER STEWART |