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| #553125 (Received by flhurricane at: 4:53 AM 27.Oct.2012) TCDAT3 TROPICAL STORM SANDY DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 500 AM EDT SAT OCT 27 2012 THE STRUCTURE OF SANDY HAS NOT CHANGED MUCH OVERNIGHT. THE CYCLONE CONTINUES TO MAINTAIN AN AREA OF DEEP CONVECTION NEAR AND NORTHWEST OF THE CENTER AND A DEEP WARM CORE. HOWEVER...DRY AIR AT THE MID AND UPPER LEVEL IS FULLY ENTRAINED INTO THE EASTERN PORTION OF THE CIRCULATION. THE CENTRAL PRESSURE REMAINS STEADY AROUND 969 MB... BUT AIRCRAFT DATA SUGGEST THAT THE PEAK WINDS HAVE DECREASED TO AROUND 60 KT WHILE THE CYCLONE CONTINUES TO GROW IN SIZE. THE STRONGEST WINDS APPEAR TO BE LOCATED IN THE CONVECTIVE BAND WEST AND NORTHWEST OF THE CENTER...WHERE RECENT SFMR AND DROPSONDE DATA SHOWED A LARGE AREA OF WINDS AROUND 55 KT. WHILE A LITTLE WEAKENING OF THE PEAK WINDS IS EXPECTED DURING THE NEXT DAY OR SO...DIFFLUENCE ASSOCIATED WITH THE UPPER-LEVEL TROUGH WEST OF SANDY SHOULD CONTINUE TO MAINTAIN A DEEP CENTRAL PRESSURE. AS SANDY INTERACTS WITH A POTENT SHORTWAVE TROUGH IN A COUPLE OF DAYS...THE GLOBAL MODELS SHOW THE CYCLONE STRENGTHENING DUE TO BAROCLINIC FORCING WHILE THE WIND FIELD CONTINUES TO GROW IN SIZE. THE NHC FORECAST SHOWS SANDY AGAIN REACHING HURRICANE STRENGTH AT 48 HOURS...WITH SOME ADDITIONAL DEEPENING POSSIBLE BEFORE LANDFALL DURING EXTRATROPICAL TRANSITION. MODEL FIELDS SUGGEST THAT SANDY WILL BE EXTRATROPICAL BY 72 HOURS AND THAT IS REFLECTED IN THE OFFICIAL FORECAST. SANDY HAS TURNED NORTH-NORTHEASTWARD WITH AN INITIAL MOTION OF 020/09. THE OVERALL TRACK FORECAST REASONING REMAINS UNCHANGED...AS SANDY WILL ACCELERATE NORTHEASTWARD TODAY AND TONIGHT AHEAD OF A DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES. A SHARP NORTHWESTWARD TURN TOWARD THE U.S. EAST COAST IS EXPECTED AFTER 48 HOURS AS SANDY INTERACTS WITH THE AFOREMENTIONED SHORTWAVE MOVING INTO THE CAROLINAS. NOT SURPRISINGLY...THERE REMAINS SOME SPREAD IN THE GUIDANCE IN THE TIMING AND LOCATION OF LANDFALL...BUT THE MOST NOTABLE TREND THIS CYCLE IS TOWARD A FASTER MOTION AS THE CYCLONE TURNS NORTHWESTWARD. THE NHC FORECAST HAS BEEN TRENDED IN THAT DIRECTION AND SHOWS THE CENTER INLAND AT 72 HOURS. OTHERWISE...THE NEW NHC TRACK IS ALONG THE PREVIOUS ONE AND LIES ROUGHLY BETWEEN THE ECMWF AND THE GFS THROUGH 72 HOURS. REGARDLESS OF THE EXACT STRUCTURE AND LANDFALL LOCATION...SANDY IS EXPECTED TO BE A LARGE AND POWERFUL CYCLONE WITH SIGNIFICANT IMPACTS EXTENDING WELL AWAY FROM THE LOCATION OF THE CENTER. NOTE THAT WIND HAZARDS FOR SANDY NORTH OF THE TROPICAL STORM WARNING AREA ARE BEING HANDLED BY HIGH WIND...STORM...AND GALE WATCHES AND WARNINGS ISSUED BY LOCAL NATIONAL WEATHER SERVICE OFFICES. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 28.6N 76.7W 60 KT 70 MPH 12H 27/1800Z 29.8N 75.8W 60 KT 70 MPH 24H 28/0600Z 31.4N 74.2W 55 KT 65 MPH 36H 28/1800Z 33.2N 72.5W 60 KT 70 MPH 48H 29/0600Z 35.7N 71.6W 65 KT 75 MPH 72H 30/0600Z 40.0N 75.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 31/0600Z 41.5N 77.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 01/0600Z 43.5N 77.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ FORECASTER BRENNAN |
