ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION TWELVE-E DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM PDT WED SEP 08 2004 THERE HAS BEEN A MODEST INCREASE IN THE OVERALL AMOUNT OF DEEP CONVECTION OVER THE PAST SEVERAL HOURS...BUT THE BASIC STRUCTURE HAS NOT CHANGED. EASTERLY SHEAR IS KEEPING THE LOW-LEVEL CIRCULATION CENTER LOCATED NEAR AND JUST UNDERNEATH THE NORTHEAST EDGE OF THE CONVECTION. DVORAK INTENSITY ESTIMATES RANGE FROM 25 TO 35 KT FROM THE THREE AGENCIES. THE QUIKSCAT PASS FROM LATE LAST NIGHT SUGGESTED PEAK WINDS WERE AT LEAST 30 KT AND SO THE INITIAL INTENSITY ESTIMATE IS INCREASED TO THAT VALUE FOR THIS ADVISORY. QUIKSCAT AMBIGUITIES AND MORNING MICROWAVE DATA INDICATE THAT THE DEPRESSION IS MOVING AT 270/8. SYNOPTIC STEERING IS BEING PROVIDED BY A MID- TO UPPER-LEVEL HIGH OVER BAJA CALIFORNIA THAT IS FORECAST BY GLOBAL MODELS TO PERSIST OVER THE NEXT COUPLE OF DAYS...AND THIS PATTERN SHOULD RESULT IN A WEST-NORTHWESTERLY TRACK OVER THAT TIME FRAME. BY DAY THREE...THE CYCLONE IS EXPECTED TO BE SOUTH OF A WEAKNESS IN THE SUBTROPICAL RIDGE THAT WOULD PROVIDE AN OPPORTUNITY FOR A MORE NORTHWARD TRACK. HOWEVER...NONE OF THE EXPLICIT TRACK GUIDANCE TAKES THE CYCLONE INTO THIS WEAKNESS...PERHAPS BECAUSE THE MODELS GENERALLY KEEP THE SYSTEM QUITE WEAK THROUGHOUT THE FORECAST PERIOD. ADDITIONAL UNCERTAINTY STEMS FROM A POOR INITIALIZATION OF THE LOW-LEVEL VORTEX...WHICH APPEARS TO RESULT IN A SPURIOUS NORTHWEST TRACK INITIALLY IN THE GFS AND GFDL. I AM INCLINED TO DISCOUNT THIS NORTHWEST TRACK IN FAVOR OF CONTINUITY WITH THE CURRENT MOTION ESTIMATE. THE OFFICIAL FORECAST IS ADJUSTED SOUTH OF THE PREVIOUS ADVISORY FOR THE FIRST 72 HOURS...AND IS SLIGHTLY NORTH OF AND SLOWER THAN THE PREVIOUS ADVISORY AFTER THAT. CIMSS ANALYSES SHOW 25 KT OF EASTERLY SHEAR OVER THE DEPRESSION. GLOBAL MODELS SUGGEST THAT THIS SHEAR WILL PERSIST OVER THE NEXT 36 HOURS OR SO...AND THE OFFICIAL FORECAST SHOWS ONLY SLOW STRENGTHENING DURING THIS TIME. SSTS UNDER THE FORECAST TRACK DECREASE SLIGHTLY OVER THE NEXT FIVE DAYS...SO IF THE SHEAR GRADUALLY DIMINSHES AS EXPECTED THE CYCLONE WILL LIKELY BE SLOW TO SPIN DOWN. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 08/1500Z 15.2N 111.3W 30 KT 12HR VT 09/0000Z 15.4N 112.6W 35 KT 24HR VT 09/1200Z 15.9N 114.5W 40 KT 36HR VT 10/0000Z 16.5N 116.5W 45 KT 48HR VT 10/1200Z 17.0N 119.0W 55 KT 72HR VT 11/1200Z 17.5N 123.5W 55 KT 96HR VT 12/1200Z 18.0N 129.0W 45 KT 120HR VT 13/1200Z 18.5N 135.0W 35 KT $$ NNNN
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Page last modified: Wednesday, 08-Sep-2004 14:34:33 UTC