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| #149902 (Received by flhurricane at: 11:05 AM 08.Sep.2007) TCDAT2 SUBTROPICAL STORM GABRIELLE DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072007 1100 AM EDT SAT SEP 08 2007 MORNING VISIBLE IMAGERY REVEALS A FULLY EXPOSED BUT WELL-DEFINED LOW-LEVEL CENTER OF CIRCULATION. DEEP CONVECTION...BUT WITH RELATIVELY WARM CLOUD TOPS NEAR -65C...REMAINS CONFINED NORTH OF THE CENTER AND IS MOST ABUNDANT IN THE NORTHWESTERN QUADRANT WITH A DISTANT AND THINNING BAND TO THE NORTHEAST. A QUIKSCAT OVERPASS AT ABOUT 1115Z CAPTURED ONLY THE WESTERN HALF OF THE CIRCULATION...BUT DID INDICATE SOME BELIEVABLE 40 KT RETRIEVALS BETWEEN ABOUT 60 AND 90 NMI FROM THE CENTER...SO THE ADVISORY INTENSITY REMAINS 40 KT. EVEN THOUGH THE CONVECTION IS BECOMING MORE PERSISTENT NEAR THE CENTER...THE STATUS REMAINS SUBTROPICAL GIVEN THAT THE RADIUS OF MAXIMUM WINDS REMAINS LARGE. A SHIP WITH CALL SIGN DDSB2 RECENTLY REPORTED WINDS OF 33 KT AND A PRESSURE OF 1011 MB ABOUT 20 NMI NORTHWEST OF THE CENTER...SO THE CENTRAL PRESSURE IS LOWERED SLIGHTLY TO 1009 MB. AN AIR FORCE RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE GABRIELLE THIS AFTERNOON TO HELP US GET A MORE THOROUGH LOOK AT THE WIND FIELD. THE CENTER OF GABRIELLE IS MOVING JUST SLIGHTLY TO THE RIGHT OF THE PREVIOUS OFFICIAL TRACK...AND THE INITIAL MOTION ESTIMATE IS 305/9...WHICH IS ALSO A TAD SLOWER THAN BEFORE. THE STORM CONTINUES TO BE STEERED BY THE RIDGE TO ITS NORTHEAST...AND THE FORECAST SCENARIO REMAINS THAT GABRIELLE WILL ROTATE AROUND THE WESTERN PERIPHERY OF THIS RIDGE AND INTO THE MIDLATITUDE WESTERLIES DURING THE NEXT 2-3 DAYS. THE LATEST MODEL GUIDANCE HAS GENERALLY SHIFTED SLIGHTLY TO THE RIGHT...AND ESPECIALLY GIVEN THE INITIAL MOTION...SO HAS THE OFFICIAL FORECAST. THE NEW TRACK IS CLOSE TO A BLEND OF THE HWRF...GFDL...AND GFS AND SHOWS LANDFALL ALONG THE OUTER BANKS IN ABOUT 36 HOURS. THE SPREAD IN THE MODELS IS SUFFICIENTLY LARGE...HOWEVER...THAT A LANDFALL FARTHER EAST OR NO LANDFALL OF THE CENTER AT ALL ARE BOTH POSSIBILITIES. AFTER PASSING NEAR OR OVER EASTERN NORTH CAROLINA...GABRIELLE SHOULD MOVE FAIRLY QUICKLY BACK OUT TO SEA AND BECOME EXTRATROPICAL BY DAY 4. A SHORT WINDOW OF OPPORTUNITY EXISTS FOR GABRIELLE TO STRENGTHEN BEFORE REACHING NORTH CAROLINA...SINCE THE CURRENT SOUTHEASTERLY WIND SHEAR IS FORECAST BY THE GLOBAL MODELS TO TEMPORARILY LESSEN TONIGHT BEFORE INCREASING AGAIN TOMORROW AS THE UPPER-LEVEL LOW TO THE SOUTHWEST MOVES FARTHER AWAY. GIVEN THE LIMITED EXTENT OF THE CONVECTION CURRENTLY...THAT CHANGE IN ENVIRONMENT IS PROBABLY NOT ENOUGH TO WARRANT A FORECAST OF SIGNIFICANT STRENGTHENING. THE NEW OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY IN BRINGING GABRIELLE TO 55 KT BY 36 HOURS...IN LINE WITH MOST OF THE OBJECTIVE GUIDANCE. GRADUAL WEAKENING IS FORECAST BEYOND 72 HOURS AS EXTRATROPICAL TRANSITION OCCURS. FORECAST POSITIONS AND MAX WINDS INITIAL 08/1500Z 31.5N 74.2W 40 KT 12HR VT 09/0000Z 32.4N 75.3W 45 KT...TROPICAL 24HR VT 09/1200Z 33.8N 76.0W 50 KT 36HR VT 10/0000Z 35.2N 75.6W 55 KT...NEAR NC COAST 48HR VT 10/1200Z 36.4N 74.0W 55 KT 72HR VT 11/1200Z 39.0N 68.0W 55 KT 96HR VT 12/1200Z 44.0N 58.0W 50 KT...EXTRATROPICAL 120HR VT 13/1200Z 46.0N 46.0W 45 KT...EXTRATROPICAL $$ FORECASTER KNABB |
