WDPN31 PGTW 120900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (CONSON) WARNING NR 026// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.3N 109.2E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 67 NM SOUTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: EASTWARD AT 01 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH WELL DEFINED LOW LEVEL CLOUD BANDS WRAPPING INTO A CLEAR CENTER. ANIMATED RADAR IMAGERY PROVIDES ADDITIONAL SUPPORT AND LENT HIGH CONFIDENCE TO THE INITIAL POSITION. THE SYSTEM HAS REMAINED STATIONARY OVER THE PAST SIX HOURS, WITH ONLY VERY SLIGHT MOVEMENTS TOWARDS THE EAST. THE INITIAL INTENSITY OF 30 KNOTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON PGTW CURRENT INTENSITY ESTIMATES OF 30 KNOTS, SUPPORTED BY A 120254Z ASCAT PASS WHICH SHOWED A SMATTERING OF 30 KNOT WINDS BOTH SOUTH AND NORTH OF THE LLCC. WHILE THE ADT CURRENT INTENSITY IS ASSESSED AT 41 KNOTS, THE RAW DATA T-NUMBER IS ONLY 1.5 (25 KNOTS) AND MORE SUPPORTIVE OF THE TRUE INTENSITY. ENVIRONMENTAL CONDITIONS ARE MARGINALLY UNFAVORABLE WITH HIGH (25-30 KTS) VWS OFFSETTING WEAK DIVERGENT OUTFLOW ALOFT AND WARM SSTS. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A WEAK SUBTROPICAL RIDGE (STR) TO THE NORTH, A NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH AND AN EXTENSION OF A DEEP-LAYER STR EXTENDING SOUTHEAST OVER THE PHILIPPINES. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS CIMSS ADT: 41 KTS AT 120540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 25-30 KTS SST: 27-28 CELSIUS OUTFLOW: WEAK WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 18W IS CURRENTLY EMBEDDED IN A COMPLEX STEERING PATTERN WITH THREE RIDGES COMPETING TO DOMINATE THE STEERING FLOW. OVER THE NEXT 12 HOURS, THE RIDGE TO THE NORTH IS FORECAST TO WEAKEN AND MOVE EASTWARD, WHILE THE RIDGE TO THE EAST BUILDS IN OVER THE SOUTH CHINA SEA AND PUSHES TD 18W OUT OF ITS CURRENT QUASI-STATIONARY POSITION. THROUGH THE REMAINDER OF THE FORECAST PERIOD THE SYSTEM WILL TRACK NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF DEEP SUBTROPICAL RIDGING. THE SYSTEM IS EXPECTED TO MAKE LANDFALL NEAR DA NANG, VIETNAM IN ABOUT 24 HOURS, BEFORE PROCEEDING FURTHER INLAND. DUE TO THE PERSISTENT HIGH VWS, THE SYSTEM IS NOT EXPECTED TO INTENSIFY, AND WILL MAINTAIN ITS CURRENT INTENSITY THROUGH LANDFALL. ONCE OVER LAND, TERRAIN INTERACTION WILL LEAD TO RAPID DISSIPATION NO LATER THAN TAU 48. MODEL DISCUSSION: THE BULK OF THE TRACK GUIDANCE, WITH THE EXCEPTION OF NAVGEM, SUPPORTS A TURN TO THE NORTH BY TAU 12, FOLLOWED BY AN ACCELERATION NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD, THOUGH THE GFS AND HWRF SOLUTIONS KEEP THE TRACK OFFSHORE UNTIL TAU 48. THE JTWC FORECAST IS A BIT FURTHER EAST THAN THE PREVIOUS FORECAST, AND CLOSELY TRACKS THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. THE JTWC INTENSITY FORECAST IS HELD SLIGHTLY HIGHER THAN THE GUIDANCE THROUGH TAU 12, THEN FOLLOWS THE CONSENSUS MEAN THEREAFTER WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN