WDPN31 PGTW 281500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 016// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.7N 112.4E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 310 NM SOUTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 22 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: VERTICAL WIND SHEAR (VWS) HAS EASED (CURRENTLY LOW TO MODERATE, 15-20 KNOTS) OVER THE PAST 12 HOURS ALLOWING DEEP CONVECTION TO REBUILD OVER THE LOW-LEVEL CIRCULATION CENTER (LLCC) AS REVEALED IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY. HOWEVER, DRY AIR ENTRAINMENT AND UPWELLING COOLER WATER CONTINUES TO HINDER SIGNIFICANT DEVELOPMENT. A 280959Z SSMIS 91GHZ MICROWAVE IMAGE INDICATES CURVED DEEP CONVECTIVE BANDING OVER THE WESTERN SEMICIRCLE BUT SHOWS NO DEEP CONVECTION OVER THE EASTERN SEMICIRCLE. THE SSMIS 37GHZ IMAGE DEPICTS SLIGHTLY IMPROVED LOW-LEVEL STRUCTURE, WITH SHALLOW BANDING WRAPPING AROUND A WEAK MICROWAVE EYE FEATURE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. A 281039Z RCM-3 SAR IMAGE ALSO SUPPORTS THE INITIAL POSITION REVEALING AN ELONGATED CENTER, WITH 50-56 KNOT MAXIMUM WINDS. THIS SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 50 KNOTS WITH HIGH CONFIDENCE. CIMSS OBJECTIVE INTENSITY ESTIMATES HAVE CONTINUED TO BE TOO LOW RANGING FROM 30-40 KNOTS WHILE AGENCY SUBJECTIVE ESTIMATES RANGE FROM 35-55 KNOTS. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT, WITH A SUBTROPICAL RIDGE (STR) TO THE EAST AND ANOTHER STR POSITIONED TO THE NORTHWEST OVER SOUTHEAST ASIA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.5 - 55 KTS RCTP: T3.5 - 55 KTS KNES: T2.5 - 35 KTS DEMS: T3.0 - 45 KTS CIMSS SATCON: 40 KTS AT 280959Z CIMSS ADT: 32 KTS AT 281130Z CIMSS AIDT: 30 KTS AT 281130Z CIMSS D-MINT: 35 KTS AT 281031Z CIMSS D-PRINT: 33 KTS AT 281240Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 33W IS EMBEDDED IN A COMPLEX STEERING ENVIRONMENT, WITH A BROAD SUBTROPICAL RIDGE (STR) TO THE EAST AND ANOTHER STR TO THE NORTH. CONSEQUENTLY, TS 33W IS FORECAST TO TRACK SLOWLY POLEWARD THROUGH TAU 36 ALONG THE WESTERN PERIPHERY OF THE STR POSITIONED TO THE EAST. THE SYSTEM WILL MAINTAIN INTENSITY NEAR 50 KNOTS DUE TO DRY AIR ENTRAINMENT, PERSISTENT SOUTHERLY VERTICAL WIND SHEAR, AND POSSIBLY COOL UPWELLING WATER. AFTER TAU 36, THE SYSTEM IS FORECAST TO TRACK SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE WESTERN STR, WITH STEADY WEAKENING AS THE SYSTEM APPROACHES VIETNAM. MODEL DISCUSSION: DETERMINISTIC GUIDANCE IS IN POOR AGREEMENT WITH A LARGE SPREAD THROUGH THE FORECAST PERIOD. IN GENERAL, THE BULK OF THE DETERMINISTIC GUIDANCE SHOWS A BRIEF 36-48 HOUR POLEWARD TRACK THEN A WESTWARD TO SOUTHWESTWARD TRACK AFTER TAU 48 TOWARD THE COAST OF VIETNAM. THE 280600Z EPS RUN SHOWS A SIMILAR TRACK AND SPREAD SUPPORTING THE JTWC TRACK FORECAST WITH MEDIUM CONFIDENCE. THE 280600Z GEFS RUN IS CHAOTIC WITH A LARGE SPREAD AND SOLUTIONS VARYING FROM A WESTWARD TRACK INTO CENTRAL VIETNAM TO A SOUTHWARD TRACK. RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 48 WITH A FAIRLY FLAT INTENSITY TREND. AFTER TAU 48, HAFS-A AND COAMPS-TC (GFS INITIAL BOUNDARY CONDITIONS), AND GFS SHOW A MODEST INTENSIFICATION TO ABOUT 55 KNOTS THEN STEADY WEAKENING THROUGH TAU 120. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: HIGH INTENSITY 72-120 HR: HIGH// NNNN