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Tropical Depression GABRIELLE Forecast Discussion Number 16
2013-09-12 10:47:43| National Hurricane Center (Atlantic)
Issued at 500 AM AST THU SEP 12 2013 000 WTNT42 KNHC 120847 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST THU SEP 12 2013 A NEW BURST OF CONVECTION HAS FORMED JUST EAST OF THE CENTER OF GABRIELLE DURING THE PAST FEW HOURS. THE SATELLITE INTENSITY ESTIMATE FROM TAFB IS 30 KT...AND AN EARLIER OSCAT OVERPASS SHOWED 25-30 KT WINDS NORTHEAST OF THE CENTER. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 30 KT. ALTHOUGH GABRIELLE REMAINS SHEARED...ANALYSES FROM CIMSS INDICATE THAT THE SHEAR HAS DECREASED TO 10-15 KT OVER THE PAST 24 HOURS. THE INITIAL MOTION IS NOW 305/6. WATER VAPOR IMAGERY AND SURFACE OBSERVATIONS SHOW A DEEP-LAYER TROUGH AND ASSOCIATED SURFACE COLD FRONT MOVING INTO THE NEW ENGLAND STATES. THE DYNAMICAL MODELS FORECAST A LOW TO FORM ON THE FRONT DURING THE NEXT 48 HOURS. THIS EVOLUTION SHOULD CREATE A BREAK IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC AND ALLOW GABRIELLE TO RECURVE INTO THE WESTERLIES. THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK...CALLING FOR A TURN TOWARD THE NORTH DURING THE NEXT 24 HOURS FOLLOWED BY A NORTH-NORTHEASTWARD ACCELERATION TOWARD ATLANTIC CANADA. THE TRACK GUIDANCE CONTINUES TO AGREE ON THIS SCENARIO...AND THE NEW TRACK IS AGAIN AN UPDATE OF THE PREVIOUS ADVISORY. THE INTENSITY FORECAST IS A LITTLE TRICKY. ON ONE SIDE...THE DECREASED SHEAR...24 HOURS BEFORE CROSSING THE NORTH WALL OF THE GULF STREAM...AND POSSIBLE INTERACTION WITH A BAROCLINIC TROUGH SUGGEST SOME POTENTIAL FOR STRENGTHENING. ON THE OTHER HAND...THE CYCLONE IS LIKELY TO MERGE WITH THE NON-TROPICAL SYSTEM IN 36-48 HOURS...AND THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT IN THE CYCLONE DECAYING TO A TROUGH IN 36 HOURS OR LESS. ON THE PREMISE THAT THE PROS WILL OUTWEIGH THE CONS...THE INTENSITY FORECAST SHOWS MODEST STRENGTHENING BEFORE EXTRATROPICAL TRANSITION. THE ALTERNATIVE SCENARIO REMAINS THAT GABRIELLE COULD DECAY TO A REMNANT LOW OR TROUGH AT ANY TIME DURING THE NEXT 48 HOURS. AFTER EXTRATROPICAL TRANSITION...THE CYCLONE OR ITS REMNANTS WILL QUICKLY BE ABSORBED BY THE LARGER NON-TROPICAL LOW. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 33.5N 67.7W 30 KT 35 MPH 12H 12/1800Z 34.4N 67.9W 30 KT 35 MPH 24H 13/0600Z 36.9N 67.5W 35 KT 40 MPH 36H 13/1800Z 41.2N 65.4W 35 KT 40 MPH 48H 14/0600Z 46.7N 61.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 15/0600Z...DISSIPATED $$ FORECASTER BEVEN
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