000 WTNT42 KNHC 120247 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 PM AST WED SEP 11 2013 DEEP CONVECTION ASSOCIATED WITH GABRIELLE HAS DISSIPATED AGAIN THIS EVENING...LEAVING THE CYCLONE AS A SWIRL OF LOW-LEVEL CLOUDS...EXCEPT FOR ONE SMALL THUNDERSTORM THAT HAS RECENTLY DEVELOPED WELL EAST OF THE CENTER. SUBJECTIVE AND OBJECTIVE DVORAK INTENSITY ESTIMATES HAVE DECREASED BELOW TROPICAL STORM STRENGTH... AND BASED ON THESE DATA THE SYSTEM HAS BEEN DOWNGRADED TO A 30-KT TROPICAL DEPRESSION. LITTLE CHANGE IN STRENGTH IS EXPECTED DURING THE NEXT 24 HOURS AS THE CYCLONE REMAINS WITHIN AN AREA OF MODERATE WESTERLY WIND SHEAR AND DRY MID-LEVEL AIR. SOME INTENSIFICATION IS POSSIBLE AS GABRIELLE INTERACTS WITH A MID- TO UPPER-LEVEL TROUGH IN 36 TO 48 HOURS. THE TROUGH IS EXPECTED TO PROVIDE SOME BAROCLINIC FORCING AND SHOULD ALSO CAUSE THE CYCLONE TO BECOME EXTRATROPICAL IN ABOUT 2 DAYS. THE SYSTEM IS LIKELY TO BE ABSORBED BY A FRONT OVER NOVA SCOTIA SHORTLY THEREAFTER...HOWEVER A 72-HOUR POINT WAS PROVIDED ONCE AGAIN FOR FORECAST CONTINUITY. WITH THE LACK OF DEEP CONVECTION THIS EVENING...AN ALTERNATIVE SCENARIO IS THAT GABRIELLE COULD DEGENERATE INTO A REMNANT LOW ON THURSDAY OR BECOME AN OPEN TROUGH AS IT BEGINS TO ACCELERATE NORTH- NORTHEASTWARD IN A DAY OR SO. GABRIELLE CONTINUES MOVING SLOWLY WEST-NORTHWESTWARD. THE CYCLONE SHOULD TURN NORTHWARD ON THURSDAY AS IT IS STEERED AROUND THE WESTERN PORTION OF A LOW- TO MID-LEVEL RIDGE OVER THE WEST-CENTRAL ATLANTIC. AFTER 24 HOURS...GABRIELLE IS FORECAST TO ACCELERATE NORTH-NORTHEASTWARD AHEAD OF THE TROUGH MOVING INTO THE NORTHEASTERN UNITED STATES. THE TRACK GUIDANCE AGREES ON THIS SCENARIO AND THE UPDATED NHC TRACK IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 33.0N 67.0W 30 KT 35 MPH 12H 12/1200Z 33.7N 67.6W 30 KT 35 MPH 24H 13/0000Z 35.7N 67.6W 30 KT 35 MPH 36H 13/1200Z 39.4N 66.1W 35 KT 40 MPH 48H 14/0000Z 44.4N 62.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 15/0000Z 54.5N 50.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 16/0000Z...ABSORBED BY FRONT $$ FORECASTER BROWN