000 WTNT43 KNHC 252037 TCDAT3 HURRICANE SANDY DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 500 PM EDT THU OCT 25 2012 SATELLITE IMAGERY SHOWS THAT STRUCTURAL CHANGES ARE ALREADY OCCURRING WITH SANDY. DRY AIR ALOFT AND SOUTHWESTERLY FLOW ASSOCIATED WITH AN UPPER-LEVEL LOW CENTERED NEAR WESTERN CUBA ARE IMPINGING ON THE WEST SIDE OF THE CIRCULATION. AS A RESULT...THE OUTFLOW IS RESTRICTED IN THE SOUTHWEST QUADRANT AND THE CLOUD PATTERN IS BECOMING MORE ASYMMETRIC. HOWEVER...THE HIGHEST FLIGHT- LEVEL WINDS FROM THE AIRCRAFT WERE STILL 109 KT AT THE END OF THE LAST MISSION AND THE CENTRAL PRESSURE REMAINS AT 963 MB. THE INITIAL INTENSITY REMAINS 90 KT FOR THIS ADVISORY. SOME DECREASE IN THE MAXIMUM WINDS IS EXPECTED DURING THE NEXT COUPLE OF DAYS AS SANDY BECOMES MORE ENTANGLED WITH THE UPPER-LEVEL LOW...HOWEVER THE GLOBAL MODELS SHOW SANDY REMAINING A VERY DEEP CYCLONE AND THE WIND FIELD EXPANDING DURING THIS TIME. LATER IN THE PERIOD...SOME RE-INTENSIFICATION IS SHOWN AS SANDY DEEPENS AGAIN OFF THE U.S. EAST COAST WHILE IT INTERACTS WITH ANOTHER SHORTWAVE TROUGH. REGARDLESS...SANDY IS EXPECTED TO BE A LARGE CYCLONE AT OR NEAR HURRICANE INTENSITY THROUGH MOST OF THE FORECAST PERIOD. THE INITIAL MOTION ESTIMATE IS 360/17...AS SANDY HAS BEGUN TO ACCELERATE NORTHWARD DUE TO THE UPPER LOW. THE REASONING FOR THE TRACK FORECAST REMAINS LARGELY UNCHANGED. SANDY WILL BE PULLED NORTHWESTWARD AND SLOW DOWN ON FRIDAY WHILE IT INTERACTS WITH THE UPPER-LEVEL LOW. THEN A NORTH-NORTHEASTWARD ACCELERATION IS EXPECTED BY SATURDAY AS A LONGWAVE TROUGH MOVES INTO THE EASTERN UNITED STATES. MOST OF THE TRACK MODELS NOW SHOW A TURN BACK TOWARD THE NORTHWEST BY THE END OF THE PERIOD DUE TO SANDY INTERACTING WITH AN AMPLIFYING SHORTWAVE TROUGH OVER THE CAROLINAS AND MID-ATLANTIC STATES. HOWEVER...THERE REMAIN SOME SIGNIFICANT DIFFERENCES IN THE TIMING OF THIS INTERACTION...AS THE ECMWF HAS SANDY FARTHER WEST AND INTERACTING WITH THE SHORTWAVE SOONER RELATIVE TO MOST OF THE REST OF THE GUIDANCE...WHICH SHOWS A WIDER TURN AND A TRACK FARTHER NORTH. THE NEW NHC FORECAST IS CLOSE TO THE PREVIOUS ONE...AND LIES ROUGHLY BETWEEN THE ECMWF AND THE GFS ENSEMBLE MEAN. REGARDLESS OF THE EXACT TRACK OF SANDY...IT IS LIKELY THAT SIGNIFICANT IMPACTS WILL BE FELT OVER PORTIONS OF THE U.S. EAST COAST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. NOTE THAT THE TROPICAL CYCLONE WIND SPEED PROBABILITIES ARE NOT DESIGNED TO HANDLE THE TYPE OF STRUCTURAL CHANGES ANTICIPATED WITH SANDY DURING THE FORECAST PERIOD. AS A RESULT...THESE PROBABILITIES WILL UNDERESTIMATE THE ACTUAL RISK OF STRONG WINDS AWAY FROM THE CENTER OF SANDY. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 24.5N 75.6W 90 KT 105 MPH 12H 26/0600Z 26.0N 76.0W 85 KT 100 MPH 24H 26/1800Z 27.4N 77.0W 80 KT 90 MPH 36H 27/0600Z 28.3N 77.0W 75 KT 85 MPH 48H 27/1800Z 29.8N 76.0W 65 KT 75 MPH 72H 28/1800Z 33.0N 73.0W 70 KT 80 MPH 96H 29/1800Z 37.5N 72.5W 70 KT 80 MPH 120H 30/1800Z 40.5N 75.0W 55 KT 65 MPH...POST-TROPICAL $$ FORECASTER BRENNAN