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| #552486 (Received by flhurricane at: 5:05 AM 25.Oct.2012) TCDAT3 HURRICANE SANDY DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012 500 AM EDT THU OCT 25 2012 EARLIER THIS MORNING...SANDY MADE LANDFALL JUST WEST OF SANTIAGO DE CUBA AS A STRONG CATEGORY TWO HURRICANE. CUBAN RADAR DATA AND REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATED THAT SANDY HAD A WELL-DEFINED 20-24 N MI DIAMETER EYE WHEN IT MADE LANDFALL. THE AIRCRAFT REPORTED MAXIMUM 700-MB FLIGHT-LEVEL WINDS OF 117 KT AND BIAS-CORRECTED SFMR SURFACE ESTIMATES OF 91-92 KT. A BLEND OF THESE DATA YIELDS A SURFACE WIND ESTIMATE OF 99 KT...JUST BELOW MAJOR HURRICANE STATUS. THE MAIN REASON WHY SANDY WAS HELD JUST BELOW MAJOR HURRICANE STATUS WAS DUE TO THE SUSTAINED 68-KT WIND AND GUST TO 99 KT THAT OCCURRED AROUND 0517Z. HOWEVER... STRONGER WINDS MAY HAVE OCCURRED LATER WHEN THE SOUTHEASTERN PORTION OF THE EYEWALL MOVED ONSHORE...WHICH IS THE QUADRANT WHERE THE 117-KT FLIGHT-LEVEL WIND WAS OBSERVED. THE INITIAL INTENSITY OF 90 KT IS BASED ON WIND DECAY MODELS FOR HURRICANES OVER LAND. THE INITIAL MOTION IS 005/16 KT. AFTER A SLIGHT JOG TO THE NORTH-NORTHEAST VERY EARLY THIS MORNING...SANDY APPEARS TO HAVE RESUMED A NORTHWARD MOTION...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS OR SO. AFTER THAT...A DEEP-LAYER TROUGH OVER THE NORTHERN U.S. AND A SIMILAR DEEP-LAYER TROUGH OVER THE NORTH ATLANTIC EAST OF NEWFOUNDLAND ARE FORECAST TO AMPLIFY... WHICH WILL INDUCE MID-LEVEL RIDGING NEAR THE NORTHEAST U.S. COAST BETWEEN THOSE TWO SYSTEMS. THAT RIDGE IS EXPECTED TO CAUSE SANDY TO SLOW DOWN AND TURN TOWARD THE NORTH-NORTHWEST IN 24-36 HOURS. AFTER THAT...THE RIDGE TO THE NORTH OF SANDY IS FORECAST TO WEAKEN AS AN APPROACHING DEEP MID-LATITUDE TROUGH MOVES OVER THE EASTERN HALF OF THE UNITED STATES BY 72 HOURS AND BEGINS TO ACCELERATE SANDY TO THE NORTHEAST. THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS DEVELOPING SCENARIO. AFTER THAT...HOWEVER...THE GUIDANCE DIVERGES SIGNIFICANTLY WITH THE ECMWF...GFDL...AND NOGAPS TAKING SANDY NORTHWESTWARD AND INLAND OVER THE DELMARVA PENINSULA BY 120 HOURS...WHEREAS THE GFS MODEL KEEPS SANDY MOVING NORTHEASTWARD AWAY FROM THE U.S. AND OVER THE OPEN NORTH ATLANTIC. THE REMAINDER OF THE MODEL GUIDANCE IS SOMEWHERE IN BETWEEN THESE TWO EXTREMES. GIVEN THE HISTORICAL RELIABILITY OF THE VERY CONSISTENT ECMWF MODEL OVER THE PAST 2 DAYS...THE OFFICIAL FORECAST WAS TURNED SLIGHTLY MORE TOWARD THE NORTHWEST AT 120 HOURS...AND IS CLOSE TO A BLEND OF THE CONSENSUS MODELS TV15 AND TVCN...AND THE FSU TRACK MODEL. OWING TO THE HIGHER CURRENT INTENSITY OF SANDY...THE NEW INTENSITY FORECAST IS ALSO HIGHER THAN THE PREVIOUS FORECAST THROUGH 36 HOURS...AND THEN IS SIMILAR TO THE PREVIOUS ADVISORY INTENSITY FORECAST AS INCREASING SHEAR BEGINS TO AFFECT THE CYCLONE. THE MAIN FORECAST CHALLENGE IS DETERMINING JUST HOW MUCH BAROCLINIC INFLUENCE THE DEEP TROUGH OVER THE EASTERN U.S. WILL HAVE ON SANDY...AND ALSO WHAT THE VERTICAL STRUCTURE OF SANDY WILL BE AFTER 48 HOURS. ALL OF THE GLOBAL MODELS MAINTAIN SIGNIFICANT RAINFALL AMOUNTS IN EXCESS OF 2 INCHES NEAR THE CENTER THROUGH 120 HOURS... WHICH SUGGESTS THAT SANDY WILL MAINTAIN SOME CONVECTION AND POSSIBLY AN INNER-CORE WARM STRUCTURE THAT WOULD KEEP SOME TROPICAL CHARACTERISTICS ASSOCIATED WITH THE SYSTEM. THE NEW INTENSITY FORECAST IS SIMILAR TO THE LGEM AND DECAY-SHIPS INTENSITY MODELS. THE FORECAST WILL STILL CALL FOR SANDY TO BECOME POST-TROPICAL BY 120 HOURS...ALTHOUGH THIS REMAINS LOW CONFIDENCE. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 20.9N 75.8W 90 KT 105 MPH 12H 25/1800Z 23.1N 75.7W 85 KT 100 MPH 24H 26/0600Z 25.4N 76.1W 80 KT 90 MPH 36H 26/1800Z 26.8N 76.6W 75 KT 85 MPH 48H 27/0600Z 28.1N 76.3W 70 KT 80 MPH 72H 28/0600Z 31.2N 73.7W 65 KT 75 MPH 96H 29/0600Z 34.5N 70.5W 65 KT 75 MPH 120H 30/0600Z 37.5N 70.5W 60 KT 70 MPH...POST-TROPICAL $$ FORECASTER STEWART |
