ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION FIFTEEN-E DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM PDT WED SEP 28 2005 TROPICAL DEPRESSION 15-E HAS BECOME A LITTLE BETTER ORGANIZED EVEN THOUGH CONVECTION HAS DECREASED IN COVERAGE AND INTENSITY SOMEWHAT. CONVECTIVE BANDING HAS IMPROVED AND NEARBY SHIP REPORTS INDICATE THE SURFACE WIND FIELD HAS BECOME BETTER DEFINED. AT 1200Z... SHIP MCDW9 LOCATED 100 NMI NORTHEAST OF THE CENTER REPORTED AN EAST-SOUTHEAST WIND OF 24 KT AND SHIP MKYJ8 LOCATED 120 NMI WEST OF THE CENTER REPORTED A NORTHWEST WIND OF 20 KT AND A PRESSURE OF 1006.8 MB. THESE OBSERVATIONS... ALONG WITH A SATELLITE INTENSITY ESTIMATE OF T2.0/30 KT FROM TAFB AND SAB...SUPPORT AN INITIAL INTENSITY OF 30 KT AND A CENTRAL PRESSURE OF AT LEAST 1005 MB. THE INITIAL MOTION ESTIMATE REMAINS 270/06. WATER VAPOR IMAGERY AND UPPER-AIR DATA INDICATE A BROAD EAST-WEST ORIENTED SUBTROPICAL RIDGE LOCATED ACROSS TEXAS AND NORTHERN MEXICO. THIS FEATURE SHOULD KEEP TD-15E MOVING IN A WEST TO WEST-NORTHWESTWARD MOTION FOR THE NEXT 36-48 HOURS. AFTER THAT...A MID-LEVEL SHORTWAVE TROUGH IS FORECAST BY ALL OF THE MODELS TO DIG SOUTHWARD FROM THE FAR NORTHEASTERN PACIFIC AND ERODE THE WESTERN PORTION OF THE RIDGE... AND POSSIBLY EVEN DEVELOP A CLOSED LOW OFF THE CALIFORNIA COAST BY 120 HOURS. THE MAIN DIFFERENCE IN THE MODELS IS THE TIMING AND DEGREE OF EROSION OF THE RIDGE. THE GFDL AND UKMET MODELS ARE THE FASTEST AND STRONGEST WITH ERODING THE RIDGE...AND THOSE MODELS RECURVE THE CYCLONE ACROSS BAJA CALIFORNIA IN 96-120 HOURS. IN CONTRAST... THE GFS...GFS-ENSEMBLE...AND THE NOGAPS MODELS ARE SLOWER AND WEAKER WITH EROSION OF THE RIDGE. GIVEN THE LACK OF SIGNIFICANT DATA OFF THE CALIFORNIA COAST AND THE RATHER WEAK LOOKING APPEARANCE OF THE TROUGH IN WATER VAPOR IMAGERY... THE OFFICIAL FORECAST IS A BLEND OF THE NHC MODEL GUIDANCE AND ALSO LEANS CLOSER TO THE PREVIOUS FORECAST TRACK... WHICH TURNS THE CYCLONE NORTHWESTWARD BY 72 HOURS. IT SHOULD BE POINTED OUT THAT NONE OF THE GLOBAL MODELS INITIALIZED TD-15E VERY WELL... SO THERE MAY BE SOME SIGNIFICANT TRACK CHANGES IN SUBSEQUENT FORECASTS. THE VERTICAL SHEAR IS CURRENTLY NEAR 20 KT AND IS NOT EXPECTED TO WEAKEN SIGNIFICANTLY UNTIL AFTER 36 HOURS. IN THE 48-84 HOUR TIME FRAME... THE SHEAR IS FORECAST TO DECREASE TO 5 KT OR LESS... WHICH SHOULD ALLOW FOR MORE SIGNIFICANT STRENGTHENING TO OCCUR SINCE THE CYCLONE WILL ALSO BE OVER 28-29C SSTS. BY DAYS 4 AND 5... THE CYCLONE IS EXPECTED TO MOVE OVER SLIGHTLY COOLER WATER... WHICH MAY BRING ABOUT SOME SLOW WEAKENING. HOWEVER... IF THE SYSTEM MOVES SLOWER THAN CURRENTLY FORECAST... IT WOULD REMAIN OVER 27-29C SSTS ... AND THE OFFICIAL INTENSITY FORECAST WOULD BE TOO LOW IN THE LATER PERIODS. THE OFFICIAL INTENSITY FORECAST FOLLOWS THE TREND OF THE SHIPS INTENSITY MODEL...BUT IS A LITTLE HIGHER AT 48H AND 72H. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 28/1500Z 17.0N 105.7W 30 KT 12HR VT 29/0000Z 17.3N 106.8W 35 KT 24HR VT 29/1200Z 17.9N 108.2W 40 KT 36HR VT 30/0000Z 18.7N 109.7W 45 KT 48HR VT 30/1200Z 19.7N 111.1W 55 KT 72HR VT 01/1200Z 21.0N 112.5W 65 KT 96HR VT 02/1200Z 22.5N 113.5W 60 KT 120HR VT 03/1200Z 24.5N 114.5W 55 KT $$ NNNN
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Page last modified: Wednesday, 28-Sep-2005 14:40:20 UTC