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| #450326 (Received by flhurricane at: 4:37 PM 15.Aug.2011) TCDAT2 TROPICAL STORM GERT DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072011 500 PM AST MON AUG 15 2011 RADAR DATA FROM BERMUDA AND SATELLITE IMAGERY INDICATE GERT HAS CHANGED LITTLE IN APPEARANCE SINCE THE PREVIOUS ADVISORY. THE LAST RECON FLIGHT LEG THROUGH THE SOUTHEAST QUADRANT PRODUCED AN 850 MB FLIGHT-LEVEL WIND OF 61 KT...WHICH EQUATES TO ROUGHLY 49 KT AT THE SURFACE. GIVEN THE APPARENT STEADY NATURE OF THE CYCLONE...THE INTENSITY IS BEING HELD AT 50 KT FOR THIS ADVISORY...WHICH IS CLOSE TO A BLEND OF SATELLITE ESTIMATES OF 55 KT FROM TAFB AND 45 KT FROM SAB...RESPECTIVELY . UPPER-LEVEL OUTFLOW IS FAIR IN ALL QUADRANTS...EXCEPT RESTRICTED TO THE NORTHEAST. THERE IS NO CHANGE TO THE PREVIOUS FORECAST RATIONALE. GERT HAS MOVED NORTH OF THE SUBTROPICAL RIDGE AXIS AND IS NOW MOVING TO THE NORTH-NORTHEAST OR 020/12. A GRADUAL TURN TOWARD THE NORTHEAST ACCOMPANIED BY A STEADY INCREASE IN FORWARD SPEED IS EXPECTED THROUGH THE REMAINDER OF THE FORECAST PERIOD AS GERT COMES UNDER THE INFLUENCE OF INCREASING SOUTHWESTERLY FLOW AHEAD OF A LARGE DEEP-LAYERED MID-LATITUDE TROUGH CURRENTLY MOVING EASTWARD OFF THE U.S. EAST COAST. THE NHC FORECAST TRACK IS A LITTLE TO EAST OF THE PREVIOUS ADVISORY TRACK AFTER 12 HOURS...AND LIES ALONG THE EXTREME RIGHT SIDE OF THE NHC GUIDANCE ENVELOPE. THE WINDOW OF OPPORTUNITY FOR GERT TO INTENSIFY IS GRADUALLY COMING TO A CLOSE. THE CYCLONE WILL BE OVER AT LEAST 26C SSTS FOR ANOTHER 12 HOURS OR SO WHILE THE VERTICAL SHEAR IS STILL LOW. ALTHOUGH THE OFFICIAL INTENSITY FORECAST ONLY CALLS FOR GERT TO REACH 55 KT...IT IS POSSIBLE THAT CYCLONE COULD REACH 60 KT BETWEEN THE 12- AND 24-HOUR FORECAST PERIODS DURING THE NOCTURNAL CONVECTIVE MAXIMUM PERIOD AROUND 12Z TUESDAY MORNING. BY 36 HOURS...GERT WILL BE OVER NEAR-20C SSTS AND UNDERGOING EXTRATROPICAL TRANSITION. THE POST-TROPICAL LOW IS THEN FORECAST TO MERGE WITH A FRONTAL SYSTEM OVER THE FAR NORTH ATLANTIC SHORTLY AFTER 48 HOURS. THE INTENSITY FORECAST CLOSELY FOLLOWS THE SHIPS AND LGEM MODEL SOLUTIONS...AND EXTRATROPICAL INTENSITY FORECASTS PROVIDED BY THE NOAA OCEAN PREDICTION CENTER. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 33.2N 62.7W 50 KT 60 MPH 12H 16/0600Z 35.7N 60.8W 55 KT 65 MPH 24H 16/1800Z 38.9N 57.1W 55 KT 65 MPH 36H 17/0600Z 41.7N 51.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 17/1800Z 44.6N 45.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 18/1800Z...DISSIPATED $$ FORECASTER STEWART |
