000 WTPZ42 KNHC 310254 TCDEP2 TROPICAL STORM BARBARA DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022007 800 PM PDT WED MAY 30 2007 THE BANDING FEATURES EVIDENT EARLIER TODAY HAVE MOSTLY DIMINISHED...RELEGATING THE DEEP CONVECTION TO ONE CLUSTER VERY NEAR THE CIRCULATION CENTER. DVORAK DATA-T NUMBERS FROM TAFB AND SAB HAVE BOTH COME DOWN TO 2.5 BUT A BLEND OF THE CI VALUES SUPPORTS MAINTAINING THE ADVISORY INTENSITY AT 40 KT. BARBARA FELL IN THE GAP BETWEEN QUIKSCAT SWATHS TONIGHT...SO THERE IS NOTHING TO CONFIRM OR DENY THE INTENSITY ESTIMATE. THE TRACK FORECAST REMAINS EXTREMELY LOW-CONFIDENCE. NOT ONLY ARE THERE SIGNIFICANT DISAGREEMENTS AMONG THE PRIMARY DYNAMICAL MODELS...THE ENSEMBLES BASED ON INDIVIDUAL MODELS SUCH AS THE GFS AND ECMWF ARE ALL OVER THE PLACE TOO. FOR EXAMPLE...THE CONTROL RUN OF THE 12Z ECMWF FORECASTS BARBARA TO BE PICKED UP BY THE TROUGH OVER THE GULF OF MEXICO AND TO MOVE INLAND OVER GUATEMALA IN LESS THAN 72 HOURS...WHILE ITS VARIOUS ENSEMBLE MEMBERS INCLUDE NORTHWESTWARD TRACKS ALONG THE PACIFIC COAST OF MEXICO. MEANWHILE THE GFS...WHICH HAD BEEN ADAMANT ABOUT A NORTHEASTWARD TRACK...HAS DRAMATICALLY SHIFTED AND NOW FORECASTS A RELATIVELY BRISK NORTHWESTWARD MOTION TO THE SOUTH OF THE MEXICAN RIDGE ON DAYS 4 AND 5. OTHER MODELS SUCH AS GFDL AND NOGAPS ARE IN BETWEEN...BUT THEY LOSE THE CIRCULATION IN THREE OR FOUR DAYS NEAR THE GULF OF TEHUANTEPEC. ALL OF THE MODEL FLIP-FLOPPING GIVES ME LITTLE JUSTIFICATION TO SHIFT THE OFFICIAL TRACK IN ANY DIRECTION...SO IT IS VERY SIMILAR TO THE PREVIOUS ADVISORY. THIS TRACK IS SLOW SOUTHWARD FOR A DAY OR SO...THEN SLOW NORTHWARD TOWARD THE WEAKNESS IN THE SUBTROPICAL RIDGE...WITH A SUBTLE WESTWARD BEND ON DAYS 4 AND 5 WHEN THE MODELS FORECAST THE RIDGE TO BUILD SLIGHTLY OVER THE GULF OF MEXICO. WATER VAPOR IMAGERY REVEALS THAT THE MID-LEVEL NORTHERLY FLOW BEHIND THE GULF OF MEXICO TROUGH HAS REACHED THE CENTER OF BARBARA...WITH THE ANTICIPATED INHIBITING EFFECTS ON THE INTENSITY. THAT PATTERN SHOULD GRADUALLY ABATE DURING THE NEXT COUPLE OF DAYS...AND BARBARA WILL STILL BE OVER VERY WARM WATERS AND IN AN ENVIRONMENT OF WEAK VERTICAL WIND SHEAR. THEREFORE...GRADUAL STRENGTHENING IS FORECAST IN ACCORDANCE WITH MOST OF THE INTENSITY GUIDANCE. IN GENERAL... THE NEW OFFICIAL FORECAST IS ONLY ADJUSTED VERY SLIGHTLY DOWNWARD AS COMPARED TO THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INITIAL 31/0300Z 13.0N 96.9W 40 KT 12HR VT 31/1200Z 12.6N 96.8W 45 KT 24HR VT 01/0000Z 12.4N 96.7W 50 KT 36HR VT 01/1200Z 12.7N 96.5W 55 KT 48HR VT 02/0000Z 13.1N 96.3W 60 KT 72HR VT 03/0000Z 14.0N 96.0W 65 KT 96HR VT 04/0000Z 15.0N 96.5W 70 KT 120HR VT 05/0000Z 15.5N 97.5W 70 KT $$ FORECASTER KNABB