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| #539983 (Received by flhurricane at: 4:41 AM 04.Sep.2012) TCDAT2 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 |
