000 WTNT43 KNHC 030257 TCDAT3 TROPICAL STORM LEE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011 1000 PM CDT FRI SEP 02 2011 SATALLITE...SURFACE...AND RECONNAISSANCE AIRCRAFT DATA INDICATE THAT LEE HAS BEEN MOVING SLOWLY NORTHWARD THIS EVENING. THE CENTER IS LOCATED TO THE SOUTHWEST OF A BURST OF DEEP CONVECTION THAT DEVELOPED LATE THIS AFTERNOON AND HAS BEEN EXPANDING IN SIZE THIS EVENING. WIND REPORTS FROM BUOYS AND OIL RIGS OVER THE GULF AND DATA FROM THE AIRCRAFT INDICATE THAT INTENSITY OF THE TROPICAL STORM REMAINS AROUND 40 KT. LEE IS CURRENTLY LOCATED TO THE SOUTHWEST OF A MID-LEVEL RIDGE THAT IS CENTERED OVER THE OHIO VALLEY. THIS RIDGE IS FORECAST TO WEAKEN AND SLIDE EASTWARD DURING THE NEXT DAY OR SO...AS A MID-LATITUDE TROUGH MOVES INTO THE NORTH-CENTRAL UNITED STATES. THIS SHOULD ALLOW LEE TO MOVE SLOWLY NORTHWARD DURING THE NEXT 24-36 HOURS. AS THE TROUGH PASSES NORTH OF THE TROPICAL STORM IN 36-48 HOURS...THE MODELS SUGGEST THAT LEE WILL SLOW DOWN AND MEANDER NEAR OR OVER SOUTHERN LOUISIANA. AFTER THAT TIME...THE TROUGH IS FORECAST TO INTERACT WITH THE CYCLONE AND LEE SHOULD MOVE NORTHEASTWARD AT A FASTER FORWARD SPEED AND BECOME EXTRATROPICAL LATE IN THE PERIOD. THE MODEL GUIDANCE IS IN GENERAL AGREEMENT WITH THIS SCENARIO... HOWEVER THERE ARE SOME LARGE DIFFERENCE IN THE FORWARD SPEED OF LEE ESPECIALLY AFTER 48 HOURS. THE NEW OFFICIAL FORECAST IS A BLEND OF THE GFS AND ECMWF MODELS AND IS A LITTLE FASTER THAN THE PREVIOUS ADVISORY...MAINLY DUE TO THE MORE NORTHWARD INITIAL POSITION. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF LEE...SINCE TROPICAL STORM CONDITIONS AND HEAVY RAINFALL EXTEND WELL AWAY OF THE CENTER. A SMALL UPPER-LEVEL LOW TO THE NORTHWEST OF LEE CONTINUES TO IMPART ABOUT 15-20 KT OF SOUTHWESTERLY SHEAR OVER THE TROPICAL CYCLONE. THIS UPPER-LOW IS FORECAST TO WEAKEN DURING THE NEXT 12-24 HOURS...WHICH SHOULD PROVIDE A MORE FAVORABLE UPPER AIR ENVIRONMENT AND ALLOW FOR GRADUAL STRENGTHENING. THE NHC INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY THROUGH LANDFALL AND IS IN GOOD AGREEMENT WITH THE SHIPS/LGEM GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 28.2N 91.6W 40 KT 45 MPH 12H 03/1200Z 28.6N 91.6W 50 KT 60 MPH 24H 04/0000Z 29.4N 91.5W 55 KT 65 MPH 36H 04/1200Z 30.0N 91.3W 50 KT 60 MPH...INLAND 48H 05/0000Z 30.2N 91.0W 45 KT 50 MPH...INLAND 72H 06/0000Z 31.5N 89.0W 40 KT 45 MPH...INLAND 96H 07/0000Z 34.0N 87.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/0000Z 35.5N 86.0W 20 KT 25 MPH...POST-TROP/EXTRATROP $$ FORECASTER BROWN