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Tropical Storm LESLIE


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
 
TROPICAL STORM LESLIE DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
500 AM AST TUE SEP 04 2012
 
AFTER AN EARLIER BURST OF DEEP CONVECTION SHORTLY AFTER THE PREVIOUS
ADVISORY...CLOUD TOPS HAVE WARMED CONSIDERABLY. ALTHOUGH THE
SHEARED CONVECTIVE CLOUD SHIELD HAS TAKEN ON A SMOOTHER
APPEARANCE...THE INTENSITY WILL REMAIN AT 55 KT BASED ON DVORAK
CI-VALUES OF T3.5/55 KT FROM BOTH TAFB AND SAB.

MICROWAVE FIXES THAT ARRIVED AFTER THE PREVIOUS ADVISORY SUGGEST
THAT LESLIE HAD...IN FACT...MOVED LITTLE...BUT WAS ALSO LOCATED A
LITTLE FARTHER TO THE EAST. THE GENERAL MOTION TREND OF THE OVERALL
CLOUD MASS NOW SUGGESTS THAT LESLIE HAS RESUMED A SLOW NORTHWARD
MOTION OF 360/03 KT. WATER VAPOR IMAGERY AND SATELLITE-DERIVED
WINDS INDICATE A DEEP-LAYER TROUGH NORTH-NORTHEAST OF LESLIE HAS
BYPASSED THE CYCLONE WHILE A SHORTWAVE RIDGE OFF THE CAROLINAS IS
BUILDING EASTWARD IN THE WAKE OF THE TROUGH. THE INCREASED RIDGING
TO THE NORTH OF LESLIE IS EXPECTED TO HINDER ANY SIGNIFICANT
FORWARD MOTION FOR THE NEXT 4 DAYS. BY DAY 5...HOWEVER...A LARGE
MID-TROPOSPHERIC TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST IS
FORECAST TO DIG SOUTHEASTWARD INTO THE TENNESSEE VALLEY BY DAY 5
AND GRADUALLY BEGINS TO LIFT THE CYCLONE NORTH-NORTHWESTWARD. 
THE OFFICIAL TRACK FORECAST IS NUDGED SLIGHTLY TO THE EAST OF THE
PREVIOUS TRACK THROUGH DAY 3...AND THEN IS BACK ON TRACK AT DAYS 4
AND 5. THIS SCENARIO CLOSELY FOLLOWS THE CONSENSUS MODEL TVCN.

LITTLE OR NO INTENSIFICATION IS EXPECTED THROUGH 36 HOURS DUE TO
MODERATE WEST-NORTHWESTERLY VERTICAL WIND SHEAR IMPINGING ON THE
CYCLONE. HOWEVER...GRADUAL STRENGTHENING IS FORECAST AT 48 HOURS
AND BEYOND AS THE SHEAR DECREASES AND AN IMPRESSIVE UPPER-LEVEL
ANTICYCLONE BUILDS OVER LESLIE. AN UPPER-LEVEL TROUGH CURRENTLY
OVER THE NORTHWESTERN BAHAMAS...IN CONJUNCTION WITH ANOTHER
UPPER-LEVEL TROUGH FORECAST TO DEVELOP ALONG 50W LONGITUDE...IS
EXPECTED TO ENHANCE THE OUTFLOW OF LESLIE ON DAY 5. THE GFS-BASED
SHIPS AND LGEM MODELS APPEAR TO BE SUFFERING FROM NEGATIVE FEEDBACK
AT DAYS 4-5 CAUSED BY 200/250 MB WARMING DUE TO THE GFS MODEL
MAKING LESLIE A SIGNIFICANT TROPICAL CYCLONE BY THAT TIME. IN
FACT...THE ECMWF ALSO IS FORECASTING SIGNIFICANT DEVELOPMENT OF
LESLIE ON DAYS 4-5...AS INDICATED BY 130-KT 850 MB WINDS ON DAY 5.
THE GFS IS SIMILAR IN STRENGTH WITH 115-KT 850 MB WINDS ALSO ON DAY
5. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS 
ADVISORY...BUT SHOWS A SLIGHTLY HIGHER INTENSITY ON DAY 5...WHICH
IS CLOSER TO THE CONSENSUS INTENSITY MODEL ICON.
 
WIND RADII WERE ADJUSTED IN ALL QUADRANTS BASED ON A 04/0054 UTC
ASCAT OVERPASS AND A 37-KT WIND REPORT FROM SHIP DPJK...WHICH WAS
LOCATED ABOUT 180 NMI SOUTH OF THE CENTER. DUE TO THE LARGE SIZE OF
LESLIE AND ITS EXPECTED SLOW MOTION...LARGE SWELLS PROPAGATING AWAY
FROM THE TROPICAL CYCLONE WILL AFFECT BERMUDA AND NEARLY ALL OF
THE U.S. EAST COAST FOR MUCH OF THIS WEEK.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0900Z 24.7N  62.5W   55 KT  65 MPH
 12H  04/1800Z 25.3N  62.5W   55 KT  65 MPH
 24H  05/0600Z 25.9N  62.6W   55 KT  65 MPH
 36H  05/1800Z 26.4N  62.6W   55 KT  65 MPH
 48H  06/0600Z 26.7N  62.6W   60 KT  70 MPH
 72H  07/0600Z 27.6N  63.1W   70 KT  80 MPH
 96H  08/0600Z 29.1N  64.1W   80 KT  90 MPH
120H  09/0600Z 32.0N  65.3W   90 KT 105 MPH
 
$$
FORECASTER STEWART
 
NNNN


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Page last modified: Monday, 31-Dec-2012 12:09:33 UTC