ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:42 UTC