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| #456439 (Received by flhurricane at: 5:06 PM 04.Sep.2011) TCDAT3 TROPICAL STORM LEE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011 400 PM CDT SUN SEP 04 2011 WSR-88D RADAR DATA AND SATELLITE IMAGERY INDICATE THAT LEE HAS BECOME A LITTLE BETTER ORGANIZED EVEN THOUGH THE CENTER IS WELL INLAND NOW OVER SOUTH-CENTRAL LOUISIANA. OTHER THAN THE STRONG BURST OF DEEP CONVECTION THAT HAS DEVELOPED NEAR THE SURFACE CENTER...NARROW BANDS OF MODEST CONVECTION CONTINUE TO FORM OVER SOUTHEASTERN LOUISIANA AND NEAR THE FLORIDA PANHANDLE...WHICH EXTEND SOUTHWARD OVER THE GULF OF MEXICO FOR A COUPLE HUNDRED MILES. SOME OF THESE BANDS HAVE CONTAINED DOPPLER VELOCITIES OF 60-68 KT FROM 4500-10000 FT IN 25-35 DBZ ECHOES...WITH MEAN VALUES OF ABOUT 55 KT. ALTHOUGH THESE DOPPLER VELOCITY VALUES WOULD TYPICALLY TRANSLATE TO SURFACE WINDS OF 45-50 KT...THE WEAK ECHO RETURNS SUGGEST THAT HIGHER WIND SPEEDS WILL MAINLY OCCUR IN GUSTS. THE INITIAL INTENSITY IS BEING MAINTAINED AT 40 KT BASED ON SUSTAINED WIND REPORT OF 40 KT FROM THE BURAS C-MAN STATION...AND THE GUST DIFFERENTIAL IN THE FORECAST/ADVISORY PRODUCT REMAINS AT 55 KT... WHICH IS A LITTLE HIGHER THAN THE STANDARD 50-KT GUST VALUE IN ORDER TO ACCOUNT FOR THE TRANSIENT STRONGER WINDS ALOFT NOTED IN DOPPLER VELOCITY DATA. LEE HAS BEEN MOVING TO THE NORTH OVER THE PAST 6 HOURS. HOWEVER... THE CYCLONE IS EXPECTED TO SLOW DOWN AND TURN TO THE NORTHEAST OR EAST-NORTHEAST WITHIN THE NEXT 6 TO 12 HOURS. OTHERWISE...THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS TRACK FORECAST REASONING. A VIGOROUS SHORTWAVE TROUGH OVER THE NORTHERN AND CENTRAL PLAINS IS EXPECTED TO CONTINUE DIGGING SOUTHEASTWARD AND GRADUALLY LIFT OUT TO THE NORTHEAST AT A SLIGHTLY FASTER FORWARD SPEED. BY 36 HOURS... A PIECE OF ENERGY FROM THE SHORTWAVE IS FORECAST BY ALL OF THE MODELS TO BREAK OFF AND BECOME ABSORBED INTO THE CIRCULATION. THIS MID-LEVEL BAROCLINIC INTERACTION...COUPLED WITH ABSORPTION BY A FRONTAL SYSTEM...IS EXPECTED TO TRANSITION LEE INTO A LARGE LOW-LATITUDE EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE TENNESSEE VALLEY BY DAYS 2-4. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND CLOSELY FOLLOWS THE CONSENSUS TRACK MODELS... TVCN AND TVCA. ALL OF THE GLOBAL AND REGIONAL MODELS ARE NOW FORECASTING LEE TO REMAIN A TROPICAL STORM OR EXTRATROPICAL GALE AREA FOR THE NEXT 36 HOURS OR SO AS THE CYCLONE GETS A SHOT OF BAROCLINIC ENERGY FROM AN UPSTREAM SHORTWAVE TROUGH. THIS TREND WAS FOLLOWED IN THE OFFICIAL INTENSITY FORECAST...AND IS A BLEND OF THE INTENSITY CONSENSUS MODEL ICON...AND INPUT FROM THE NHC TAFB UNIT. 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 04/2100Z 30.6N 91.8W 40 KT 45 MPH 12H 05/0600Z 30.7N 91.0W 35 KT 40 MPH...INLAND 24H 05/1800Z 31.2N 89.6W 35 KT 40 MPH...INLAND 36H 06/0600Z 32.3N 88.3W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 06/1800Z 33.3N 87.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 07/1800Z 34.8N 86.8W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 08/1800Z 36.0N 86.8W 20 KT 25 MPH...POST-TROP/EXTRATROP 120H 09/1800Z...DISSIPATED $$ FORECASTER STEWART |
