WDPN31 PGTW 241500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SEPAT) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.6N 140.1E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 283 NM SOUTH OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DECOUPLING LOW-LEVEL CIRCULATION CENTER THAT CONTINUES ON A NORTH-NORTHWESTWARD TRACK WHILE DEEP CONVECTION IS SHEARED SOUTHWARD. THE SYSTEM REMAINS IN AN UNFAVORABLE ENVIRONMENT WITH STRONG VERTICAL WIND SHEAR FROM THE UPPER-LEVEL TROUGH TO THE NORTH AND THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE SOUTHWEST. WATER VAPOR IMAGERY HIGHLIGHTS HOW OUTFLOW HAS CEASED AS THE UPPER-LEVEL TROUGH HAS MOVED EASTWARD, PUTTING THE SYSTEM IN CLOSE PROXIMITY TO THE CONVERGENT REGION OF THE TROUGH. SIMULTANEOUSLY, THE TUTT CELL TO THE SOUTHWEST HAS CUT OFF THE WESTWARD EXHAUST CHANNEL, PREVENTING A FAVORABLE UPPER-LEVEL ENVIRONMENT OVERALL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 241128Z GPM GMI 37GHZ MICROWAVE IMAGE REVEALING THE SHALLOW LOW-LEVEL CIRCULATION CENTER THAT COULD NOT HAVE BEEN IDENTIFIES EASILY ON ANIMATED EIR. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW ALONGSIDE A PARTIAL 241204Z METOP-C ASCAT WIND VECTOR IMAGE REVEALING 25-30KTS IN THE EASTERN PERIPHERY OF THE CIRCULATION. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.5 - 35 KTS KNES: T2.5 - 35 KTS CIMSS SATCON: 40 KTS AT 240937Z CIMSS ADT: 43 KTS AT 241120Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 15-20 KTS SST: 24-25 CELSIUS OUTFLOW: WEAK RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 02W WILL TRACK NORTH-NORTHWESTWARD FOR THE NEXT 12 HOURS UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE TO THE NORTHEAST. BETWEEN TAU 12-24, THE SYSTEM WILL ROUND THE RIDGE AXIS AND BEGIN A NORTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD. VERTICAL WIND SHEAR WILL REMAIN UNFAVORABLE FOR THE FIRST 24 HOURS OF THE FORECAST, RESULTING IN SLIGHT WEAKENING TO 30KTS BY TAU 12. AFTER TAU 24, VERTICAL WIND SHEAR WILL LESSEN, BUT AN APPROACHING UPPER-LEVEL TROUGH AND COOL SEA SURFACE TEMPERATURES WILL CAUSE THE SYSTEM TO BEGIN EXTRATROPICAL TRANSITION BY TAU 36. DURING THE EXTRATROPICAL TRANSITION, BAROCLINIC FORCING WILL ALLOW FOR SLIGHT INTENSIFICATION FROM TAU 36 UNTIL TAU 48. EXTRATROPICAL TRANSITION WILL COMPLETE BY TAU 72 AT AN INTENSITY OF 30KTS. MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN STRONG AGREEMENT THAT THE SYSTEM WILL ROUND THE STR TO THE NORTHEAST, BUT THE TRACK SPEED VARIES SLIGHTLY BETWEEN THE JTWC CONSENSUS MEMBERS. NAVGEM IS SIGNIFICANTLY SLOWER THAN THE BULK OF THE CONSENSUS MEMBERS, WITH AN ALONG-TRACK SPREAD OF 275NM BY TAU 48. THE INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, INDICATING A CONSISTENT INTENSITY BETWEEN 30-35TS FOR THE REMAINDER OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN