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| #455953 (Received by flhurricane at: 10:54 AM 03.Sep.2011) TCDAT3 TROPICAL STORM LEE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011 1000 AM CDT SAT SEP 03 2011 DATA FROM RECONNAISSANCE AIRCRAFT AND NOAA DOPPLER WEATHER RADARS INDICATE THAT LEE HAS STRENGTHENED A LITTLE MORE THIS MORNING. LONG PATCHES OF DOPPLER VELOCITIES OF 58-70 KT BETWEEN 2500-9500 FEET IN AREAS OF 35-45 DBZ RADAR ECHOES HAVE BEEN NOTED OVER WATER AND OVER LAND IN EXTREME SOUTHEASTERN LOUISIANA. RECON DATA ALSO INDICATED 60-KT 850 MB FLIGHT-LEVEL WINDS IN THE SAME GENERAL AREA AS THE DOPPLER VELOCITIES. THIS INFORMATION SUPPORTS AN INTENSITY OF 50 KT. THERE ARE TWO LOW-LEVEL CIRCULATION CENTERS APPARENT IN SATELLITE IMAGERY...AND THE INITIAL POSITION AND FORWARD MOTION OF 005/05 KT IS BASED ON THE MEAN POSITION BETWEEN THOSE TWO VORTICES...WHICH IS CLOSE TO THE RECON 850 MB FLIGHT-LEVEL CENTER. THE GLOBAL AND REGIONAL MODELS ARE GENERALLY IN GOOD AGREEMENT ON THE FORECAST TRACK FOR THE NEXT 72 HOURS OR SO. UPPER-AIR DATA THIS MORNING INDICATES THE WESTERN EDGE OF THE BLOCKING HIGH OVER THE SOUTHEASTERN U.S. IS BEGINNING TO ERODE AS A SHORTWAVE TROUGH OVER THE SOUTHERN AND CENTRAL U.S. PLAINS STATES MOVES SLOWLY EASTWARD. WEAK SOUTHERLY FLOW DEVELOPING ON THE WEST SIDE OF THE RIDGE SHOULD SLOWLY LIFT LEE NORTHWARD ACROSS CENTRAL LOUISIANA DURING THE NEXT 24 HOURS OR SO. AS THE TROUGH APPROACHES FROM THE WEST...LEE IS FORECAST TO TURN TOWARD THE NORTHEAST AND ACCELERATE SLIGHTLY ON DAYS 2-3. BY DAY 4...IF NOT SOONER...LEE IS EXPECTED TO MERGE WITH A FRONTAL SYSTEM OVER THE SOUTHEASTERN UNITED STATES...WHICH IS VERY ACLIMATOLOGICAL FOR THIS TIME OF THE YEAR. THE MODELS DIFFER SIGNIFICANTLY WITH THE EVOLUTION AND FUTURE TRACK OF LEE ON DAYS 4 AND 5 WITH THE ECMWF KEEPING LEE UNDER A LARGE CUTOFF LOW FORECAST TO DEVELOP OVER THE OHIO VALLEY...WHILE THE OTHER MODELS RACE THE REMNANTS OF LEE OFF TO THE NORTHEAST UNDER A MORE PROGRESSIVE MID-LATITUDE FLOW PATTERN. GIVEN THE RUN-TO-RUN CONSISTENCY OF THE ECMWF THE PAST COUPLE OF DAYS...THE NHC TRACK LEANS TOWARD THE ECMWF MODEL IN MOVING LEE MORE SLOWLY TO THE NORTHEAST ON DAYS 4 AND 5. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY...AND LIES TO RIGHT OF THE NHC MODEL CONSENSUS USING THE ECMWF MODEL TRACK SPEEDS. LEE IS NOT EXPECTED TO STRENGTHEN MUCH...IF ANY...DUE TO THE ENTRAINMENT OF AN ABUNDANCE OF VERY DRY AIR INTO THE SOUTHWESTERN SEMICIRCLE OF THE CYCLONE. HOWEVER...DUE TO THE VERY LARGE SIZE OF THE CIRCULATION...ONLY SLOW WEAKENING IS EXPECTED EVEN AFTER LEE MOVES INLAND OVER LOUISIANA LATER TODAY. THE 34-KT WIND RADII WERE EXPANDED IN THE NORTHEAST SEMICIRCLE BASED ON 43-KT SUSTAINED WINDS REPORTED AT NOAA BUOY 42040. IT SHOULD BE NOTED THAT THE WINDS AND RAINS OF LEE EXTEND FAR FROM THE CENTER...SO IT IS IMPORTANT NOT TO FOCUS TOO MUCH ON THE EXACT FORECAST TRACK. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 29.3N 91.8W 50 KT 60 MPH 12H 04/0000Z 29.7N 91.7W 50 KT 60 MPH 24H 04/1200Z 30.3N 91.6W 50 KT 60 MPH...INLAND 36H 05/0000Z 30.9N 91.1W 45 KT 50 MPH...INLAND 48H 05/1200Z 31.4N 90.1W 40 KT 45 MPH...INLAND 72H 06/1200Z 33.0N 87.5W 30 KT 35 MPH...INLAND 96H 07/1200Z 35.0N 84.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/1200Z 37.5N 81.0W 20 KT 25 MPH...POST-TROP/EXTRATROP $$ FORECASTER STEWART |
