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| #149835 (Received by flhurricane at: 11:17 PM 07.Sep.2007) TCDAT2 SUBTROPICAL STORM GABRIELLE DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072007 1100 PM EDT FRI SEP 07 2007 THE AIR FORCE RESERVE HURRICANE HUNTER INVESTIGATING THE LOW PRESSURE AREA OFF THE SOUTHEASTERN U. S. COAST COULD NOT FIND A WELL-DEFINED CIRCULATION...REPORTING INSTEAD A VERY ELONGATED CENTER. SUBSEQUENT SATELLITE IMAGERY SUGGESTS THE CIRCULATION IS SLIGHTLY BETTER DEFINED...BUT IS STILL BROAD AND ELONGATED. THE AIRCRAFT FOUND 48 KT FLIGHT-LEVEL WINDS ABOUT 85 N MI NORTHEAST OF THE CENTER AND A CENTRAL PRESSURE OF ABOUT 1011 MB. BASED ON THE LARGE RADIUS OF MAXIMUM WINDS...THE CONVECTIVE STRUCTURE...AND THE PROXIMITY OF AN UPPER-LEVEL LOW TO THE WEST-SOUTHWEST...THE SYSTEM IS DESIGNATED A SUBTROPICAL STORM WITH WINDS OF 40 KT. GABRIELL IS MOVING 300/8 BETWEEN A DEEP LAYER RIDGE OVER THE NORTHWESTERN ATLANTIC AND AN UPPER-LEVEL LOW NEAR THE NORTHERN BAHAMAS. THE DYNAMICAL MODELS FORECAST THE CYCLONE TO RECURVE AROUND THE WESTERN END OF THE EASTWARD-MOVING RIDGE DURING THE NEXT 48-72 HR. THE MODELS DISAGREE...HOWEVER...ON EXACTLY WHERE AND WHEN THAT TURN WILL OCCUR. THE GFDL IS THE LEFTMOST SOLUTION WITH A FORECAST TRACK INTO EASTERN SOUTH CAROLINA IN ABOUT 36 HR... FOLLOWED BY A NORTHEASTWARD MOTION ACROSS EASTERN NORTH CAROLINA INTO THE ATLANTIC. THE UKMET...NOGAPS...AND GFS CALL FOR LANDFALL IN EASTERN NORTH CAROLINA IN 36-48 HR...FOLLOWED BY RECURVATURE INTO THE ATLANTIC. THE GFDL TRACK MAY BE RESULTING FROM HAVING TOO DEEP OF A VORTEX INITIALLY...WHICH RESULTS IN TOO MUCH STEERING INFLUENCE FROM THE UPPER-LEVEL LOW. THUS...THE FORECAST TRACK FOLLOWS THE MORE EASTWARD SCENARIO OF THE OTHER MODELS. THERE ARE CURRENTLY MANY NEGATIVE FACTORS INVOLVED IN THE FUTURE DEVELOPMENT OF GABRIELLE. THE STORM HAS COOLER AIR TO THE NORTH AT LOW LEVELS...VERY DRY AIR TO THE SOUTH AND WEST AT THE UPPER LEVELS...IS EXPERIENCING SOUTHERLY VERTICAL WIND SHEAR...AND IS PASSING OVER WATERS THAT HAVE COOLED A FEW DEGREES OVER THE PAST COUPLE OF DAYS. ON THE POSITIVE SIDE...THE SHEAR MAY DECREASE AS GABRIELLE APPROACHES THE COAST...AND THIS COULD OCCUR OVER THE DEEP WARM WATER OF THE GULF STREAM. THE SHIPS MODEL CALLS FOR A PEAK INTENSITY OF 63 KT...THE GFDL 68 KT...AND THE HWRF 37 KT. GIVEN ALL THE NEGATIVES...THE INTENSITY FORECAST WILL STAY ON THE LOW SIDE OF THE GUIDANCE...CALLING FOR A PEAK INTENSITY OF 50 KT NEAR LANDFALL. AFTER RECURVATURE...GABRIELLE SHOULD GRADUALLY MERGE WITH A FRONTAL ZONE AND BECOME EXTRATROPICAL. IT SHOULD BE NOTED THAT THERE IS A POSSIBILITY OF CENTER REFORMATION DUE TO THE ELONGATED NATURE OF THE SYSTEM. WHILE SUCH REFORMATION WOULD NOT CHANGE THE OVERALL STEERING PATTERN...IT COULD HAVE AN AFFECT ON IF AND WHERE THE CENTER MAKES LANDFALL. FORECAST POSITIONS AND MAX WINDS INITIAL 08/0300Z 30.4N 72.2W 40 KT...SUBTROPICAL 12HR VT 08/1200Z 31.1N 73.7W 40 KT...SUBTROPICAL 24HR VT 09/0000Z 32.3N 75.5W 40 KT...SUBTROPICAL 36HR VT 09/1200Z 33.5N 76.8W 45 KT...TROPICAL 48HR VT 10/0000Z 35.0N 76.6W 50 KT...INLAND 72HR VT 11/0000Z 37.5N 73.5W 40 KT...OVER WATER 96HR VT 12/0000Z 40.5N 67.5W 45 KT...EXTRATROPICAL 120HR VT 13/0000Z 43.0N 58.0W 45 KT...EXTRATROPICAL $$ FORECASTER BEVEN/ROBERTS |
