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| #456301 (Received by flhurricane at: 10:52 AM 04.Sep.2011) TCDAT3 TROPICAL STORM LEE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011 1000 AM CDT SUN SEP 04 2011 SURFACE OBSERVATIONS AND WSR-88D RADAR DATA INDICATE THAT LEE FINALLY MOVED INLAND OVER SOUTH-CENTRAL LOUISIANA THIS MORNING AROUND 11Z ABOUT 10 NMI SOUTH OF INTRACOASTAL CITY. RECENT DOPPLER RADAR DATA INDICATE BANDS OF CONVECTION HAVE FORMED OVER SOUTHEASTERN LOUISIANA AND NEAR THE FLORIDA PANHANDLE AND EXTEND SOUTHWESTWARD OVER THE GULF OF MEXICO. SOME OF THESE BANDS HAVE CONTAINED DOPPLER VELOCITIES OF 65-72 KT FROM 8000-12000 FT IN 35-45 DBZ ECHOES...WITH MEAN VALUES OF AT LEAST 60 KT. ALTHOUGH THESE DOPPLER VELOCITY VALUES WOULD TYPICALLY EQUATE TO SURFACE WINDS OF 50-55 KT...THE SHORT-LIVED NATURE OF THESE NEW CONVECTIVE BANDS SUGGESTS THAT ANY HIGHER WIND SPEEDS WILL LIKELY BE VERY TRANSIENT. THE INITIAL INTENSITY IS BEING MAINTAINED AT 40 KT BASED ON WIND REPORTS FROM NOAA BUOY 42040...BUT THE GUST DIFFERENTIAL IN THE FORECAST/ADVISORY PRODUCT HAS BEEN INCREASED TO 55 KT FROM THE STANDARD 50-KT GUST VALUE IN ORDER TO ACCOUNT FOR THE STRONGER DOPPLER VELOCITIES THAT HAVE BEEN OBSERVED. LEE IS DRIFTING SLOWLY TO THE NORTHEAST...OR 040/03 KT. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. LEE IS EXPECTED TO REMAIN EMBEDDED IN A WEAK STEERING FLOW REGIME FOR THE NEXT 24 HOURS OR SO AND ONLY DRIFT SLOWLY EAST-NORTHEASTWARD TO NORTHEASTWARD. AFTER THAT...A VIGOROUS SHORTWAVE TROUGH IS FORECAST TO DIG SOUTHEASTWARD FROM THE NORTHERN AND CENTRAL PLAINS AND GRADUALLY LIFT LEE NORTHEASTWARD AT A FASTER FORWARD SPEED... BUT STILL AT LESS THAN 10 KT. BY 48 HOURS...LEE IS EXPECTED TO MERGE WITH A FAIRLY BRISK FRONTAL SYSTEM FOR THIS TIME OF THE YEAR...AND BECOME A LARGE SLOW-MOVING EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE TENNESSEE VALLEY. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY...EXCEPT THAT THE FORWARD SPEED WAS DECREASED AFTER 48 HOURS...AND CLOSELY FOLLOWS THE CONSENSUS TRACK MODELS... TVCN AND TVCA. LEE WILL BE MOVING OVER THE RAIN-SATURATED FLAT TERRAIN OF SOUTHERN AND SOUTHEASTERN LOUISIANA TODAY...WITH A LARGE PORTION OF THE CIRCULATION REMAINING OVER WATER. AFTERNOON HEATING SHOULD ALSO GENERATE DEEP CONVECTION OVER LAND AND NEAR THE CENTER OF CIRCULATION...WHICH COULD ADD SOME ENERGY TO THE CYCLONE. AS A RESULT...THE TROPICAL STORM IS EXPECTED TO WEAKEN MORE SLOWLY THAN INDICATED BY THE TYPICAL INLAND DECAY RATE FOR INLAND TROPICAL CYCLONES. SINCE HEAVY RAINS...STRONG WINDS...AND THE HIGHEST STORM SURGE VALUES ARE OCCURRING VERY FAR FROM THE CENTER...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT LOCATION OF THE CENTER OF LEE. THE PRIMARY THREAT FROM LEE WILL BE EXTREMELY HEAVY RAINFALL OVER MUCH OF THE SOUTHEASTERN U.S. DURING NEXT SEVERAL DAYS. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 29.9N 91.9W 40 KT 45 MPH...INLAND 12H 05/0000Z 30.1N 91.5W 35 KT 40 MPH...INLAND 24H 05/1200Z 30.6N 90.4W 30 KT 35 MPH...INLAND 36H 06/0000Z 31.4N 88.9W 30 KT 35 MPH...INLAND 48H 06/1200Z 32.6N 87.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 07/1200Z 34.5N 86.5W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 08/1200Z 36.5N 86.0W 20 KT 25 MPH...POST-TROP/EXTRATROP 120H 09/1200Z...DISSIPATED $$ FORECASTER STEWART |
