000 WTNT44 KNHC 240837 TCDAT4 TROPICAL STORM DEBBY DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042012 400 AM CDT SUN JUN 24 2012 THE CLOUD PATTERN OF THE TROPICAL STORM HAS NOT BECOME SIGNIFICANTLY BETTER ORGANIZED OVER THE PAST FEW HOURS. DEBBY HAS BEEN PRODUCING VERY COLD-TOPPED DEEP CONVECTION BUT THESE THUNDERSTORMS...AND LIKELY THE STRONGEST WINDS...ARE OCCURRING SOME 100 TO 150 MILES NORTHEAST OF THE LOW-LEVEL CENTER. THE CURRENT INTENSITY IS KEPT AT 45 KT...WHICH IS IN AGREEMENT WITH DATA FROM AN ASCAT PASS SEVERAL HOURS AGO. NO CHANGE IS MADE TO THE PREVIOUS INTENSITY FORECAST...HOWEVER THIS FORECAST IS BASED ON THE PREMISE THAT THE VERTICAL SHEAR WILL DECREASE OVER THE NEXT FEW DAYS AND THE GLOBAL MODELS ARE NOT UNANIMOUS ON THIS. THE OFFICIAL WIND SPEED FORECAST IS CLOSEST TO THE MOST RECENT HWRF GUIDANCE...AND IT SHOULD BE NOTED THAT WE HAVE LIMITED SKILL IN PREDICTING TROPICAL CYCLONE INTENSITY CHANGE. WITH INFRARED IMAGERY THE CENTER...ALTHOUGH PARTIALLY EXPOSED...HAS BECOME A LITTLE MORE DIFFICULT TO LOCATE AND THE FIXES FROM TAFB AND SAB ARE ABOUT 50 MILES APART. MY BEST ESTIMATE OF INITIAL MOTION IS SLOWLY NORTHWARD...OR 360/3. THE TRACK FORECAST FOR THIS STORM IS EXTREMELY CHALLENGING. THE SYNOPTIC REASONING IN PREVIOUS ADVISORIES WAS BASED ON A MID-LEVEL RIDGE BUILDING TO THE NORTH OF THE TROPICAL CYCLONE...WHICH WOULD CAUSE DEBBY TO MOVE TOWARD THE NORTHWEST GULF OF MEXICO COAST IN SEVERAL DAYS. THAT TRACK SCENARIO WAS SUPPORTED BY THE ECMWF MODEL...WHICH HAS BEEN THE BEST-PERFORMING GUIDANCE OVER THE PAST FEW YEARS. HOWEVER...THE 0000 RUN OF THAT MODEL HAS SHIFTED SUBSTANTIALLY TO THE NORTH AND EAST OF THE PREVIOUS RUNS. THE U.K. MET. OFFICE MODEL HAS ALSO SHIFTED SIGNIFICANTLY TO THE RIGHT. IN FACT...ONLY THE HWRF MODEL IS CLOSE TO THE PREVIOUS OFFICIAL FORECASTS...AND EVEN IT IS TO THE NORTH OF THEM. THEREFORE AN UNUSUALLY LARGE RIGHTWARD ADJUSTMENT TO THE NHC FORECAST IS REQUIRED...AND ADDITIONAL SHIFTS TO THE NORTH AND EAST MAY BE NECESSARY IN SUBSEQUENT ADVISORY PACKAGES. NEEDLESS TO SAY...THIS IS A LOW CONFIDENCE FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 27.3N 87.3W 45 KT 50 MPH 12H 24/1800Z 27.5N 87.4W 50 KT 60 MPH 24H 25/0600Z 27.9N 87.8W 50 KT 60 MPH 36H 25/1800Z 28.2N 88.4W 55 KT 65 MPH 48H 26/0600Z 28.3N 89.0W 60 KT 70 MPH 72H 27/0600Z 28.5N 90.5W 65 KT 75 MPH 96H 28/0600Z 28.5N 92.0W 70 KT 80 MPH 120H 29/0600Z 28.5N 93.5W 70 KT 80 MPH $$ FORECASTER PASCH