| ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE SANDY DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 1100 PM EDT FRI OCT 26 2012 SANDY IS SHOWING CHARACTERISTICS OF A HYBRID CYCLONE THIS EVENING. OVERALL...THE SYSTEM LOOKS LIKE A LARGE OCCLUDED FRONTAL LOW. HOWEVER...SURFACE OBSERVATIONS DO NOT SHOW STRONG TEMPERATURE GRADIENTS...AND CENTRAL CONVECTION IS OCCURRING IN BANDS TO THE NORTHWEST OF THE CENTER. IN ADDITION...AMSU DATA FROM NEAR 2000 UTC INDICATED THAT THE SYSTEM STILL HAD A DEEP WARM CORE. DROPSONDES AND SFMR DATA FROM A NOAA HURRICANE HUNTER AIRCRAFT SHOWED A LARGE AREA OF 60 KT WINDS TO THE WEST AND NORTHWEST OF THE CENTER...AND BASED ON THIS AND THE POSSIBILITY THAT STRONGER WINDS WERE NOT SAMPLED...THE INITIAL INTENSITY REMAINS 65 KT. AN INTERESTING NOTE IS THAT THE DROPSONDE DATA INDICATES THAT THE STRONGEST WINDS IN THE CONVECTION AT FLIGHT-LEVEL ARE SIGNIFICANTLY LESS THAN THOSE NEAR THE SURFACE. THE CENTER HAS BEEN WOBBLING DURING THE EVENING...WITH THE INITIAL MOTION A SOMEWHAT UNCERTAIN 010/6. THERE IS NO CHANGE TO THE TRACK FORECAST REASONING FROM THE PREVIOUS ADVISORY. A DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES SHOULD CAUSE SANDY TO TURN NORTHEASTWARD WITH AN INCREASE IN FORWARD SPEED...AND THIS MOTION SHOULD PERSIST FOR 48 HR OR SO. AFTER THAT...A NEGATIVELY-TILTED SHORTWAVE TROUGH NEAR THE U.S. EAST COAST AND A RIDGE OVER EXTREME EASTERN CANADA SHOULD CAUSE SANDY TO TURN TOWARD THE NORTHWEST AND WEST-NORTHWEST...TOWARD AND OVER THE U.S. COAST. THE TRACK GUIDANCE ENVELOPE SHIFTED A LITTLE TO THE EAST DURING THE FIRST 48 HR...AND THE FORECAST IS NUDGED IN THAT DIRECTION. HOWEVER...THERE WAS LITTLE CHANGE AFTER THAT TIME...AND THE LANDFALL AREA AND TIME IS CHANGED LITTLE FROM THAT OF THE PREVIOUS FORECAST. SANDY IS CURRENTLY EXPERIENCING ABOUT 50 KT OF VERTICAL WIND SHEAR WHICH IS DISRUPTING THE CONVECTIVE STRUCTURE. HOWEVER...VERY STRONG UPPER-LEVEL DIVERGENCE ASSOCIATED WITH A TROUGH SOUTHWEST OF THE HURRICANE IS LIKELY SUSTAINING THE CYCLONE. WHILE THESE CONDITIONS ARE FORECAST TO CONTINUE...IT IS LIKELY THAT SANDY WILL CONTINUE TO SLOWLY WEAKEN THROUGH 36 HR. SUBSEQUENTLY...THE DYNAMICAL MODELS FORECAST THAT INTERACTION WITH THE U. S. SHORTWAVE TROUGH WILL CAUSE SANDY TO RE-INTENSIFY PRIMARILY DUE TO BAROCLININC ENERGY PROCESSES. THE INTENSITY FORECAST SHOWS SANDY REGAINING HURRICANE STRENGTH IN 48-72 HR. HOWEVER...THE CYCLONE WILL BE UNDERGOING EXTRATROPICAL TRANSITION AS THIS HAPPENS...AND WHEN THIS PROCESS WILL BE COMPLETE IS UNCERTAIN. REGARDLESS OF THE EXACT STRUCTURE AT LANDFALL...SANDY IS EXPECTED TO BE A LARGE AND POWERFUL CYCLONE WITH SIGNIFICANT IMPACTS EXTENDING WELL AWAY FROM THE LOCATION OF THE CENTER. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 27.7N 77.1W 65 KT 75 MPH 12H 27/1200Z 28.8N 76.7W 60 KT 70 MPH 24H 28/0000Z 30.4N 75.2W 55 KT 65 MPH 36H 28/1200Z 32.0N 73.3W 55 KT 65 MPH 48H 29/0000Z 33.8N 71.9W 65 KT 75 MPH 72H 30/0000Z 37.5N 72.0W 70 KT 80 MPH 96H 31/0000Z 40.0N 77.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 01/0000Z 42.0N 76.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN NNNN |