Tropical Storm Gabrielle - 10am Wednesday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM GABRIELLE DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013
1100 AM AST WED SEP 11 2013

GABRIELLE IS BARELY HANGING ON AS A TROPICAL CYCLONE...WITH A SMALL AREA OF DEEP CONVECTION TO THE EAST OF THE EXPOSED LOW-LEVEL CENTER. THIS IS LIKELY DUE TO THE 15-20 KT OF SOUTHWESTERLY SHEAR OVER THE CYCLONE. THE INTITAL INTENSITY HAS BEEN CONSERVATIVELY LOWERED TO 40 KT FOR THIS ADVISORY. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 36 HOURS OR SO AS MODERATE SHEAR CONTINUES...BUT SOME INTENSIFICATION IS SHOWN AT 48 HOURS AS AN UPPER-LEVEL TROUGH MAY PROVIDE SOME BAROCLINIC SUPPORT FOR INTENSIFICATION. BY 72 HOURS...GABRIELLE SHOULD BE EXTRATROPICAL AND BE ABSORBED OR DISSIPATE SHORTLY THEREAFTER. ALTERNATIVELY...IF DEEP CONVECTION DISSIPATES ENTIRELY...GABRIELLE COULD BECOME A POST-TROPICAL CYCLONE AT ANY TIME DURING THE FORECAST PERIOD.

THE CYCLONE HAS BEEN MOVING LITTLE OVER THE PAST FEW HOURS...AND IS NOW DRIFTING WESTWARD AT ABOUT 3 KT. HOWEVER THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON A SLOW NORTHWESTWARD MOTION DEVELOPING DURING THE NEXT 12 TO 24 HOURS DUE TO AN UPPER-LEVEL LOW TO THE SOUTHWEST OF GABRIELLE AND A LOW/MID-LEVEL RIDGE TO THE NORTH AND NORTHEAST. RECURVATURE IS EXPECTED BY 48 HOURS AS THE CYCLONE ACCELERATES NORTH-NORTHEASTWARD AHEAD OF AN ADVANCING MID/UPPER-LEVEL TROUGH. THE TRACK MODEL GUIDANCE HAS TRENDED A LITTLE SLOWER AND TO THE LEFT THIS CYCLE AND SO HAS THE NHC TRACK WHICH NOW LIES ALONG...BUT IS A LITTLE FASTER THAN...THE TVCA MULTI-MODEL CONSENSUS.


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