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| #551915 (Received by flhurricane at: 10:59 PM 22.Oct.2012) TCDAT3 TROPICAL STORM SANDY DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 1100 PM EDT MON OCT 22 2012 SINCE THE LAST RECON FLIGHT INTO SANDY AROUND 20Z...THE EARLIER AMORPHOUS MASS OF CONVECTION EAST AND SOUTH OF THE CENTER HAS BECOME MORE CONSOLIDATED NEAR THE CENTER...AND A CENTRAL DENSE OVERCAST FEATURE APPEARS TO BE FORMING. IN ADDITION...INNER-CORE CONVECTIVE BANDING HAS DEVELOPED SOUTH AND NORTH OF THE CENTER... WITH OUTER BANDING FEATURES ALSO DEVELOPING OVER MUCH OF THE EASTERN SEMICIRCLE. UPPER-LEVEL OUTFLOW HAS EXPANDED AND IMPROVED IN ALL QUADRANTS...ESPECIALLY TO THE NORTHWEST WHERE IT HAD BEEN RESTRICTED BY AN UPPER-LEVEL TROUGH. THE INITIAL INTENSITY OF 40 KT IS BASED ON A BLEND OF EARLIER SFMR-ADJUSTED SURFACE WIND SPEEDS OF 42 KT AND 38 KT AROUND 20Z...AND THE RECENT INCREASE IN INNER-CORE CONVECTIVE ORGANIZATION. THE INITIAL MOTION ESTIMATE REMAINS STATIONARY. UPPER-AIR DATA AT 23/00Z INDICATED THAT MID-LEVEL HEIGHTS TO THE NORTH OF SANDY FROM PUERTO RICO NORTHWESTWARD TO THE SOUTHEASTERN U.S. HAVE NOT CHANGED OVER THE PAST 24 HOURS. THIS SUGGESTS...AT LEAST IN THE SHORT TERM...THAT LITTLE POLEWARD MOTION IS LIKELY. BY 12-24 HOURS AND CONTINUING THROUGH 72 HOURS...THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON A GENERAL SLOW NORTH TO NORTH-NORTHEASTWARD MOTION TOWARD JAMAICA AND EASTERN CUBA AS A SHORTWAVE MOVES OFF THE SOUTHEASTERN U.S. COAST AND WEAKENS THE SUBTROPICAL RIDGE THAT CURRENTLY EXTENDS ACROSS FLORIDA AND THE BAHAMAS. BY DAYS 4 AND 5...HOWEVER...THE MODELS BEGIN TO DIVERGE SIGNIFICANTLY WITH THE NORMALLY RELIABLE ECMWF TAKING SANDY NORTH-NORTHWESTWARD CLOSER TO THE U.S. SOUTHEAST COAST...WHEREAS THE GFS...HWRF...GFDL...AND OTHER LESS RELIABLE MODELS TAKE THE CYCLONE NORTH-NORTHEASTWARD. GIVEN THE HISTORICAL RELIABILITY OF THE ECMWF MODEL...THE OFFICIAL FORECAST TRACK REMAINS SIMILAR TO THE PREVIOUS ADVISORY TRACK...AND LIES CLOSE TO A BLEND OF THE TVCA AND TV15 CONSENSUS MODELS...AND THE FLORIDA STATE SUPERENSEMBLE MODEL. REMAINING NEARLY STATIONARY OVER THE WARM WATERS OF SOUTHWESTERN CARIBBEAN SEA IS NEVER A GOOD SIGN FOR THIS TIME OF THE YEAR. THE GFS-BASED SHIPS MODEL IS INDICATING THAT SANDY SHOULD REMAIN IN AN ENVIRONMENT OF VERTICAL SHEAR LESS THAN 5 KT...MID-LEVEL MOISTURE GREATER THAN 80 PERCENT...OVER SSTS OF 29-30C...AND OVER UPPER OCEAN HEAT CONTENT VALUES GREATER THAN 70 UNITS FOR AT LEAST THE NEXT 24 HOURS. THESE ENVIRONMENTAL PARAMETERS ARE GENERALLY CONDUCIVE FOR RAPID INTENSIFICATION TO OCCUR...AND THE SHIPS MODEL REFLECTS THIS WITH A 64 PERCENT CHANCE OF A 30-KT INTENSITY INCREASE DURING THE NEXT 24 HOURS. GIVEN THE RECENT IMPROVEMENT IN THE INNER-CORE CONVECTIVE PATTERN...THE OFFICIAL INTENSITY FORECAST HAS BEEN INCREASED OVER THE PREVIOUS ADVISORY AND NOW FORECASTS SANDY TO BECOME A HURRICANE BY 36 HOURS BEFORE THE CYCLONE REACHES JAMAICA. AFTER THAT...LAND INTERACTION WITH JAMAICA AND CUBA... COMBINED WITH INCREASING SOUTHWESTERLY VERTICAL SHEAR IS EXPECTED TO INDUCE GRADUAL WEAKENING. BY 120 HOURS...SANDY IS EXPECTED TO INTERACT WITH A DEEP UPPER-LEVEL TROUGH THAT COULD INDUCE TRANSITION INTO A SIGNIFICANT SUBTROPICAL CYCLONE. THE OFFICIAL INTENSITY FORECAST IS HIGHER THAN THE PREVIOUS ADVISORY THROUGH 48 HOURS...AND CLOSELY FOLLOWS A BLEND OF THE ICON...IV15...IVCN INTENSITY CONSENSUS MODELS. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 12.7N 78.6W 40 KT 45 MPH 12H 23/1200Z 13.6N 78.4W 50 KT 60 MPH 24H 24/0000Z 14.8N 77.9W 60 KT 70 MPH 36H 24/1200Z 16.6N 77.5W 70 KT 80 MPH 48H 25/0000Z 18.5N 77.1W 60 KT 70 MPH...INLAND OVER JAMAICA 72H 26/0000Z 22.7N 75.8W 55 KT 65 MPH...OVER WATER 96H 27/0000Z 25.7N 75.4W 55 KT 65 MPH 120H 28/0000Z 28.2N 73.6W 55 KT 65 MPH...SUBTROPICAL $$ FORECASTER STEWART |
