[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 030857
TCDAT3

TROPICAL STORM LEE DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
400 AM CDT SAT SEP 03 2011

SURFACE AND AIRCRAFT DATA INDICATE THAT LEE HAS STRENGTHENED A
LITTLE DURING THE PAST SEVERAL HOURS WITH THE MAXIMUM WINDS NOW
NEAR 45 KT AND A CENTRAL PRESSURE NEAR 995 MB.  THE CYCLONE
CONTINUES TO HAVE AN ELONGATED CENTER OF CIRCULATION AND A LARGE
RADIUS OF MAXIMUM WINDS...AND THIS...COMBINED WITH THE GENERAL
APPEARANCE IN SATELLITE IMAGERY...SUGGESTS THAT LEE HAS AT LEAST
SOME CHARACTERISTICS OF A SUBTROPICAL CYCLONE.  ANALYSES FROM CIMSS
AT THE UNIVERSITY OF WISCONSIN SUGGEST THE STORM IS EXPERIENCING
ABOUT 15 KT OF WESTERLY VERTICAL WIND SHEAR DUE TO INTERACTION WITH
AN UPPER-LEVEL TROUGH VERY CLOSE TO THE SYSTEM...AND WATER VAPOR
IMAGERY SHOWS MID/UPPER-LEVEL DRY AIR OVER THE SOUTHWESTERN
QUADRANT OF THE STORM.

THE CENTER HAS TENDED TO REFORM FROM TIME TO TIME...WHICH MAKES THE
INITIAL MOTION OF 345/6 RATHER UNCERTAIN.  MOST TRACK MODEL
GUIDANCE NOW AGREES THAT LEE SHOULD MOVE SLOWLY FOR THE NEXT 48 HR
AS A RIDGE TO THE NORTH SLOWLY WEAKENS...FIRST GENERALLY NORTHWARD
INTO SOUTHERN LOUISIANA AND THEN GENERALLY NORTHEASTWARD.  AFTER 48
HR...A DEEP-LAYER TROUGH APPROACHING FROM THE NORTH SHOULD CAUSE A
FASTER MOTION TOWARD THE NORTHEAST...ALTHOUGH THERE REMAINS SOME
SIGNIFICANT DISAGREEMENT BETWEEN THE MODELS ON THE EXACT SPEED.
THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE WEST OF THE
PREVIOUS TRACK BASED ON THE CURRENT POSITION AND MOTION...THEN LIES
NORTH OF THE PREVIOUS TRACK FROM 36 HOURS ONWARD.

GIVEN THAT THE CURRENT ISSUES WITH SHEAR AND DRY AIR HAVE NOT YET
SIGNIFICANTLY AFFECTED DEVELOPMENT...LEE IS EXPECTED TO CONTINUE
STRENGTHENING UNTIL LANDFALL.  WEAKENING AFTER LANDFALL IS LIKELY
TO BE SLOWER THAN NORMAL TO THE THE MARSHY NATURE OF THE LOUISIANA
COAST AND THE AMOUNT OF THE CIRCULATION THAT SHOULD REMAIN OVER
WATER.  LATER IN THE FORECAST PERIOD...LEE IS FORECAST TO MERGE
WITH AN ONCOMING COLD FRONT AND BECOME EXTRATROPICAL...A SOMEWHAT
UNUSUAL OCCURRENCE IN THIS AREA AT THIS TIME OF YEAR.

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  03/0900Z 28.8N  91.9W   45 KT  50 MPH
 12H  03/1800Z 29.3N  92.0W   50 KT  60 MPH
 24H  04/0600Z 30.0N  91.9W   55 KT  65 MPH...INLAND
 36H  04/1800Z 30.5N  91.5W   45 KT  50 MPH...INLAND
 48H  05/0600Z 31.0N  90.7W   40 KT  45 MPH...INLAND
 72H  06/0600Z 32.5N  88.5W   35 KT  40 MPH...INLAND
 96H  07/0600Z 35.0N  86.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
120H  08/0600Z 37.0N  82.5W   20 KT  25 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BEVEN


This weather bulletin was brought to you by:
www.nashvilleweather.net