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| #450257 (Received by flhurricane at: 10:43 AM 15.Aug.2011) TCDAT2 TROPICAL STORM GERT DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072011 1100 AM AST MON AUG 15 2011 THE PRESENTATION OF GERT IN DOPPLER RADAR IMAGERY FROM BERMUDA HAS INDICATED BRIEF PERIODIC TIGHTENING OF THE INNER CORE CIRCULATION...INCLUDING A SMALL 6-8 NMI DIAMETER EYE-LIKE FEATURE...ONLY TO HAVE THE CONVECTION WEAKEN OR DISSIPATE DUE TO INTRUSIONS OF DRY AIR. AN AIR FORCE RESERVE RECON AIRCRAFT INVESTIGATING THE CYCLONE HAS FOUND MAXIMUM 850 MB FLIGHT-LEVEL WINDS OF 53 KT AND A FEW UNCONTAMINATED 49-51 KT SFMR WINDS IN THE EASTERN SEMICIRCLE...ACCOMPANIED BY A MINIMUM PRESSURE OF NEAR 1000 MB. BASED ON THIS INFORMATION...THE INTENSITY IS SET AT 50 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 010/10 KT. THERE IS NO CHANGE TO THE PREVIOUS FORECAST REASONING. GERT HAS BEEN MOVING NORTHWARD THROUGH A BREAK IN THE SUBTROPICAL RIDGE AND HAS NOW REACHED THE AXIS OF THE EAST-WEST ORIENTED RIDGE THAT LIES ALONG 32N LATITUDE. AS THE LARGE FULL LATITUDE TROUGH CURRENTLY MOVING OFF THE U.S. EAST COAST CONTINUES ITS EASTWARD PROGRESS...GERT SHOULD GRADUALLY ACCELERATE AND TURN TOWARD THE NORTH-NORTHEAST LATER TODAY AND TOWARD THE NORTHEAST BY LATE TONIGHT OR TUESDAY. THE OFFICIAL TRACK FORECAST IS A LITTLE TO THE RIGHT OF THE PREVIOUS TRACK AND IS A BLEND OF THE ECMWF AND GFS MODEL SOLUTIONS. SOME FURTHER INTENSIFICATION OF GERT IS POSSIBLE DURING THE NEXT 24 HOURS AS THE CYCLONE REMAINS OVER RELATIVELY WARM WATER AND BENEATH AN UPPER-LEVEL ANTICYCLONE. HOWEVER...GERT IS A SMALLER THAN AVERAGE SIZE TROPICAL CYCLONE...WHICH MEANS IT WILL BE SUSCEPTIBLE TO INTRUSIONS OF DRY AIR AND SLIGHT INCREASES IN VERTICAL SHEAR. AS A RESULT...THE INTENSITY FORECAST IS BEING HELD JUST BELOW HURRICANE STRENGTH. BY 24 HOURS...GERT WILL BE MOVING OVER SEA-SURFACE TEMPERATURES COOLER THAN 26C...AND OVER WATER COOLER THAN 20C BY 48 HOURS. AS A RESULT...GRADUAL WEAKENING IS EXPECTED AFTER 24 HOURS AND EXTRATROPICAL TRANSITION IS EXPECTED TO OCCUR BY 48 HOURS WHEN THE CYCLONE BEGINS TO MERGE WITH A FRONTAL SYSTEM AND ALSO BEGINS TO FEEL THE EFFECTS OF STRONG SOUTHWESTERLY UPPER-LEVEL WIND SHEAR. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND CLOSELY FOLLOWS THE SHIPS AND LGEM MODEL SOLUTIONS. EXTRATROPICAL INTENSITY FORECASTS WERE PROVIDED BY THE NOAA OCEAN PREDICTION CENTER. THE BERMUDA WEATHER SERVICE HAS DISCONTINUED THE TROPICAL STORM WARNING FOR BERMUDA. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 32.0N 63.2W 50 KT 60 MPH 12H 16/0000Z 34.3N 62.0W 55 KT 65 MPH 24H 16/1200Z 37.8N 59.0W 60 KT 70 MPH 36H 17/0000Z 40.8N 54.6W 55 KT 65 MPH 48H 17/1200Z 43.4N 48.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 18/1200Z 48.5N 33.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 19/1200Z...DISSIPATED $$ FORECASTER STEWART |
