[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 031453
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


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