000
WTNT42 KNHC 111436
TCDAT2
 
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.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  11/1500Z 32.5N  65.9W   40 KT  45 MPH
 12H  12/0000Z 33.1N  66.5W   40 KT  45 MPH
 24H  12/1200Z 33.8N  67.1W   40 KT  45 MPH
 36H  13/0000Z 35.5N  67.2W   40 KT  45 MPH
 48H  13/1200Z 38.6N  65.9W   45 KT  50 MPH
 72H  14/1200Z 48.5N  58.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  15/1200Z...DISSIPATED
 
$$
FORECASTER BRENNAN