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| #450012 (Received by flhurricane at: 4:43 PM 14.Aug.2011) TCDAT2 TROPICAL STORM GERT DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072011 500 PM AST SUN AUG 14 2011 DEEP CONVECTION HAS CONTINUED TO DEVELOP OVER THE CENTER OF TROPICAL STORM GERT AND SMALL BANDING FEATURES HAVE BEEN TRYING TO DEVELOP IN THE NORTH AND EAST QUADRANTS OF THE CIRCULATION. AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT INVESTIGATING THE CYCLONE THIS AFTERNOON FOUND MAXIMUM 850 MB FLIGHT-LEVEL WINDS OF 43 KT IN THE SOUTHEAST QUADRANT ALONG WITH UNCONTAMINATED SFMR WINDS OF 39 AND 41 KT. THE SFMR WINDS CORRELATE WELL WITH AN EARLIER 1324Z ASCAT PASS THAT INDICATED SURFACE WINDS OF NEAR 40 KT IN THE SAME GENERAL AREA OF THE CYCLONE CIRCULATION. BASED ON THE RECENT SFMR WINDS AND EARLIER ASCAT WINDS...THE INITIAL INTENSITY IS INCREASED TO 40 KT. NOW THAT GERT HAS REDEVELOPED DEEP CONVECTION NEAR THE CENTER AND HAS BECOME A MORE VERTICALLY DEEP SYSTEM...THE TROPICAL STORM HAS STARTED MOVING NORTH-NORTHWESTWARD...OR 335/07...TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE. WATER VAPOR IMAGERY INDICATES A FAST-MOVING SHORTWAVE TROUGH PASSING EASTWARD OVER AND NORTH OF BERMUDA WITH A SHORTWAVE RIDGE IN ITS WAKE...WHICH MAY ALLOW FOR THE SUBTROPICAL RIDGE TO BRIEFLY BUILD BACK WESTWARD AND CREATE SOME STAIR-STEP MOTIONS TO THE NORTH-NORTHWEST AND NORTH. HOWEVER...ALL OF THE GLOBAL MODELS ARE IN EXCELLENT AGREEMENT ON A LARGE MID-LATITUDE TROUGH CURRENTLY OVER THE EASTERN U.S. MOVING STEADILY EASTWARD AND GRADUALLY ERODING THE WESTERN PERIPHERY OF THE MID-LEVEL RIDGE ALONG 32N LATITUDE FOR THE NEXT 24-36 HOURS. AS A RESULT... THE STEERING FLOW SHOULD BECOME MORE SOUTHERLY AND STEER GERT NORTHWARD FOR THE NEXT 24 HOURS OR SO...AND THEN ACCELERATE THE CYCLONE NORTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY THROUGH 48 HOURS AND LIES CLOSE TO THE TIGHTLY PACKED GLOBAL MODEL SUITE. GERT HAS MOVED INTO A WEAK VERTICAL SHEAR REGION ON THE NORTH SIDE OF A SMALL UPPER-LEVEL LOW...WHICH HAS ALLOWED DEEP CONVECTION TO PERSIST AND PRODUCE A SMALL UPPER-LEVEL ANTICYCLONE OVER THE STORM. THIS FAVORABLE UPPER-LEVEL FLOW REGIME...ALONG WITH WARM SSTS ABOVE 28C...IS EXPECTED TO PERSIST FOR THE NEXT 24 HOURS OT SO. THIS SHOULD ALLOW FOR AT LEAST MODEST STRENGTHENING. AFTER THAT...THERMODYNAMIC CONDITIONS ARE FORECAST BECOME LESS CONDUCIVE...WHICH SHOULD ALLOW FOR ONLY SLIGHT STRENGTHENING EVEN THOUGH THE VERTICAL SHEAR IS EXPECTED TO BE FAIRLY LOW. BY 48 HOURS...GERT WILL BE MOVING OVER MUCH COOLER WATER AND SOUTHWESTERLY VERTICAL SHEAR IS EXPECTED TO INCREASE ABOVE 30 KT. THIS COMBINATION OF UNFAVORABLE ENVIRONMENTAL CONDITIONS SHOULD CAUSE GERT TO MAKE THE TRANSITION INTO A POST-TROPICAL CYCLONE. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND CLOSELY FOLLOWS THE SHIPS AND LGEM INTENSITY MODELS. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 28.9N 63.2W 40 KT 45 MPH 12H 15/0600Z 30.3N 63.8W 40 KT 45 MPH 24H 15/1800Z 32.3N 63.6W 45 KT 50 MPH 36H 16/0600Z 34.9N 61.8W 50 KT 60 MPH 48H 16/1800Z 38.9N 58.2W 50 KT 60 MPH 72H 17/1800Z 46.0N 45.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 18/1800Z...DISSIPATED $$ FORECASTER STEWART |
