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| #552707 (Received by flhurricane at: 11:14 PM 25.Oct.2012) TCDAT3 HURRICANE SANDY DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 1100 PM EDT THU OCT 25 2012 REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATE THAT SANDY HAS WEAKENED A LITTLE THIS EVENING. THE MAXIMUM FLIGHT-LEVEL WINDS AT 8000 FT WERE 90 KT...AND DROPSONDES IN WHAT REMAINED OF THE EYEWALL SUGGESTED 70 KT SURFACE WINDS. THE CENTRAL PRESSURE HAD RISEN TO 968 MB. BASED ON THESE DATA...THE INITIAL INTENSITY IS REDUCED TO 80 KT...AND THIS COULD BE A LITTLE GENEROUS. SURFACE OBSERVATIONS INDICATE THAT THE OUTER WIND FIELD CONTINUES TO EXPAND...ESPECIALLY IN THE NORTHERN SEMICIRCLE. SANDY HAS BEGUN ITS ANTICIPATED LEFT TURN AND THE INITIAL MOTION IS NOW 335/11. THE HURRICANE SHOULD CONTINUE A GENERAL NORTH- NORTHWESTWARD MOTION FOR THE NEXT 24 HOURS OR SO AS IT INTERACTS WITH A MID/UPPER-LEVEL LOW OVER THE FLORIDA STRAITS. AFTER THAT...A DEEP-LAYER LONGWAVE TROUGH MOVING INTO THE EASTERN UNITED STATES SHOULD CAUSE SANDY TO TURN NORTHWARD AND NORTHEASTWARD. AFTER 72 HR...SANDY SHOULD INTERACT WITH A SHORTWAVE TROUGH MOVING THROUGH THE LARGER LONGWAVE...WHICH IS EXPECTED TO TURN THE CYCLONE BACK TOWARD THE NORTHWEST...A TRACK THAT SHOULD BRING THE CENTER ONSHORE IN THE NORTHEASTERN UNITED STATES. THE GUIDANCE IS IN FAIR TO GOOD AGREEMENT ON THIS...AND THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE GUIDANCE SINCE THE LAST ADVISORY. THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK...EXCEPT FOR A LITTLE MORE WESTWARD POSITION AT THE 24 HOUR POINT THAT LIES BETWEEN THE GFS AND ECMWF MODELS ON THE LEFT SIDE OF THE TRACK GUIDANCE ENVELOPE. OTHERWISE...THE TRACK IS NEAR THE CENTER OF THE GUIDANCE ENVELOPE. WATER VAPOR IMAGERY SHOWS THE UPPER-LEVEL TROUGH IS PRODUCING STRONG UPPER-LEVEL DIVERGENCE OVER AND NEAR SANDY...WHICH IS HELPING TO KEEP THE STORM GOING DESPITE 35 KT OF VERTICAL WIND SHEAR. THE RESULT OF THIS INTERACTION IS THAT SANDY SHOULD CONTINUE TO EXPAND IN SIZE...WITH A GRADUAL REDUCTION IN THE CENTRAL WINDS. LATER IN THE FORECAST PERIOD...INTERACTION WITH THE SHORTWAVE TROUGH IS EXPECTED TO CAUSE SOME RE-INTENSIFICATION AS THE CYCLONE STARTS EXTRATROPICAL TRANSITION. THIS PROCESS IS LIKELY TO BEGIN AS EARLY AS 96 HR...BUT IT IS UNCLEAR JUST HOW FAR IT WILL HAVE PROCEEDED BEFORE THE CYCLONE MAKES LANDFALL. THUS...THE FORECAST CONTINUES TO CALL FOR THE SYSTEM TO BE POST-TROPICAL IN 120 HR...WITH A VERY LOW CONFIDENCE. THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...WITH SOME MODIFICATION TO THE FIRST 36 HR DUE TO THE OBSERVED WEAKENING THIS EVENING. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 25.3N 76.1W 80 KT 90 MPH 12H 26/1200Z 26.6N 76.8W 75 KT 85 MPH 24H 27/0000Z 27.6N 77.4W 75 KT 85 MPH 36H 27/1200Z 28.9N 76.9W 70 KT 80 MPH 48H 28/0000Z 30.4N 75.4W 65 KT 75 MPH 72H 29/0000Z 34.0N 72.5W 70 KT 80 MPH 96H 30/0000Z 37.5N 72.5W 70 KT 80 MPH 120H 31/0000Z 40.5N 76.5W 55 KT 65 MPH...INLAND POST-TROPICAL $$ FORECASTER BEVEN |
