Tropical Depression GILMA

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TROPICAL DEPRESSION GILMA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP082006
200 AM PDT WED AUG 02 2006
 
EASTERLY SHEAR HAS TAKEN A TOLL ON GILMA...AS THE CONVECTION
WEST OF THE CENTER HAS LARGELY DISSIPATED LEAVING BEHIND A
WELL-DEFINED LOW-LEVEL CIRCULATION CLEARLY SEEN IN SHORTWAVE
INFRARED AND MICROWAVE IMAGERY.  DATA-T NUMBERS OF 2.0 FROM TAFB AND
SAB AND 1.0 FROM AFWA COMBINED WITH THE LACK CONVECTION RESULT IN
GILMA BEING DOWNGRADED TO A DEPRESSION. THE SHIPS MODEL INDICATES
THAT EASTERLY SHEAR WILL INCREASE IN THE NEXT DAY OR TWO AS GILMA
MOVES INTO A DRIER ENVIRONMENT...AND BOTH OF THESE FACTORS ARGUE
AGAINST RESTRENGTHENING IN THE SHORT TERM. HOWEVER...A QUICK BURST
OF CONVECTION NEAR THE CENTER COULD QUICKLY BRING GILMA BACK TO
TROPICAL STORM STRENGTH AT ANY TIME SINCE THE CIRCULATION REMAINS
WELL DEFINED. LATER IN THE PERIOD...THE SHEAR IS FORECAST TO
RELAX...HOWEVER THE ENVIRONMENT REMAINS DRY AND SEA SURFACE
TEMPERATURES DECREASE TO MARGINAL VALUES. THEREFORE THE INTENSITY
IS HELD AT 30 KT FOR THE FORECAST PERIOD.

THE SIX-HOUR MEAN MOTION IS AROUND 315/04...HOWEVER GILMA APPEARS TO
HAVE NEARLY STALLED IN THE LAST COUPLE OF HOURS AS THE IMPACT OF
THE DEEP EASTERLY SHEAR ON THE NOW SHALLOW CIRCULATION HAS
DECREASED. THE FORECAST TRACK IS SLIGHTLY TO THE RIGHT AND SLOWER
THAN THE PREVIOUS FORECAST THROUGH 96 HOURS. THIS IS DUE TO THE
SLOWER AND MORE NORTHWARD INITIAL MOTION OF GILMA IN THE PAST FEW
HOURS. THE UKMET...NOGAPS AND GFDL MODELS SHOW A STRONGER GILMA
RECURVING INTO THE UPPER TROUGH/CLOSED LOW DIGGING SOUTH OFF THE
WEST COAST.  THE GFS...GFS ENSEMBLE MEAN AND ECMWF SHOW THE TROUGH
BYPASSING GILMA... AND THIS SCENARIO IS PREFERRED WITH A WEAKER AND
MORE SHALLOW CYCLONE.  THE DAY FIVE POSITION HAS BEEN ADJUSTED TO
THE SOUTHEAST OF THE PREVIOUS FORECAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0900Z 14.6N 106.0W    30 KT
 12HR VT     02/1800Z 15.2N 106.9W    30 KT
 24HR VT     03/0600Z 15.7N 108.2W    30 KT
 36HR VT     03/1800Z 16.1N 109.8W    30 KT
 48HR VT     04/0600Z 16.6N 111.4W    30 KT
 72HR VT     05/0600Z 17.5N 114.0W    30 KT
 96HR VT     06/0600Z 19.0N 116.5W    30 KT
120HR VT     07/0600Z 20.5N 119.5W    30 KT
 
$$
FORECASTER BRENNAN/STEWART
 
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