ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM LESLIE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 500 AM AST SUN SEP 02 2012 THE CENTER OF LESLIE REMAINS SHEARED TO THE NORTHWEST OF THE MAIN CONVECTIVE CLOUD MASS. HOWEVER...CONVECTION HAS GRADUALLY BEEN DEVELOPING CLOSER TO THE CENTER OVER THE PAST 6 HOURS...AND DVORAK INTENSITY ESTIMATES FROM TAFB HAVE BEEN VARYING BETWEEN T3.0/45 KT AND T3.5/55 KT. A 02/0134 UTC ASCAT OVERPASS INDICATED A PEAK WIND VECTOR OF 51 KT SURROUNDED BY SEVERAL 50-KT VECTORS. ADJUSTING FOR THE KNOWN LOW BIAS OF ASCAT WINDS YIELDS SURFACE WIND SPEEDS OF NEAR 60 KT...AND THAT IS THE INTENSITY USED FOR THIS ADVISORY. LESLIE IS MOVING NORTHWESTWARD...OR 310/13 KT. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON LESLIE GRADUALLY TURNING NORTHWARD AND ACCOMPANIED BY A DECREASE IN FORWARD SPEED DURING THE NEXT 48 HOURS AS THE CYCLONE MOVES INTO A BREAK IN THE SUBTROPICAL RIDGE BETWEEN 60-65W LONGITUDE. BY 72 HOURS...HOWEVER...THE BROAD TROUGH/UPPER LOW CREATING THE BREAK IN THE RIDGE IS FORECAST TO LIFT OUT TO THE NORTHEAST...WHICH WILL ALLOW A TRAILING SHORTWAVE RIDGE TO BUILD IN TO THE NORTH OF LESLIE ON DAYS 4 AND 5. THIS SHOULD RESULT IN A BLOCKING FLOW PATTERN DEVELOPING AROUND THE CYCLONE THAT WILL CAUSE LESLIE TO SLOW DOWN TO LESS THAN 5 KT...AND POSSIBLY EVEN BECOME STATIONARY DURING THE LATTER FORECAST PERIODS. THE OFFICIAL FORECAST TRACK IS AN UPDATE OF THE PREVIOUS TRACK...AND IS SIMILAR TO THE CONSENSUS MODELS TVCA AND TV15. THE VERTICAL WIND SHEAR AFFECTING LESLIE IS EXPECTED TO BE MODERATE FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD CAP ANY SIGNIFICANT INTENSIFICATION. AT 36 AND 48 HOURS...THE SHEAR IS FORECAST TO INCREASE TO NEAR 30 KT...WHICH IS EXPECTED TO CAUSE THE CYCLONE TO WEAKEN SOME. ASSUMING LESLIE SURVIVES THE DAY 2 HOSTILE SHEAR CONDITIONS...THE UPPER-LEVEL WIND ENVIRONMENT IS FORECAST TO IMPROVE AND BECOME CONDUCIVE FOR SIGNIFICANT STRENGTHENING TO OCCUR. THE INTENSITY FORECAST REMAINS ON THE CONSERVATIVE SIDE AT DAYS 4 AND 5 DUE TO THE UNCERTAINTY IN JUST HOW MUCH LESLIE WILL WEAKEN OVER THE DAY 2-3 TIME PERIOD. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND REMAINS ALONG THE LOWER END OF THE GUIDANCE ENVELOPE NEAR THE SHIPS-LGEM CONSENSUS. THE INITIAL 34-KT AND 50-KT WIND RADII WERE INCREASED BASED ON WIND DATA FROM THE AFOREMENTIONED ASCAT OVERPASS...WHICH CAPTURED THE ENTIRE CIRCULATION OF LESLIE. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 20.8N 59.5W 60 KT 70 MPH 12H 02/1800Z 22.0N 60.9W 60 KT 70 MPH 24H 03/0600Z 23.7N 62.1W 60 KT 70 MPH 36H 03/1800Z 25.0N 62.6W 55 KT 65 MPH 48H 04/0600Z 25.9N 62.7W 55 KT 65 MPH 72H 05/0600Z 26.9N 62.4W 55 KT 65 MPH 96H 06/0600Z 28.0N 62.5W 65 KT 75 MPH 120H 07/0600Z 29.2N 63.0W 70 KT 80 MPH $$ FORECASTER STEWART NNNN
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Page last modified: Monday, 31-Dec-2012 12:09:33 UTC