WDPN31 PGTW 061500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 020// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 33.5N 149.6E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 473 NM EAST-SOUTHEAST OF NARITA AIRPORT MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL STORM (TS) 04W (MUN), ACCOMPANIED BY WELL-DEFINED, ALBEIT SHALLOW, CONVECTIVE BANDING FEATURES. PERSISTENT DRY AIR ENTRAINMENT HAS INHIBITED THE DEVELOPMENT AND MAINTENANCE OF DEEP CONVECTION, THOUGH THE SYSTEM CONTINUES TO EXHIBIT A COHERENT LOW-LEVEL VORTEX STRUCTURE, AND SOME STRONGER CONVECTIVE ACTIVITY IS PRESENT WITHIN THE SOUTHEASTERN QUADRANT. ENVIRONMENTAL DIAGNOSTICS INDICATE MARGINALLY UNFAVORABLE CONDITIONS, INCLUDING INCREASING (20-25 KTS) NORTHEASTERLY VERTICAL WIND SHEAR (VWS), PERSISTENT DRY AIR ENTRAINMENT, OFFSET BY BORDERLINE WARM (26-27 C) SEA SURFACE TEMPERATURES (SST) AND MODERATE EQUATORWARD UPPER-LEVEL OUTFLOW. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE, SUPPORTED BY ANIMATED INFRARED SATELLITE IMAGERY OF THE LLCC. THE INITIAL INTENSITY ESTIMATE OF 50 KTS IS ASSIGNED WITH MEDIUM CONFIDENCE, BASED ON A SYNTHESIS OF AGENCY SUBJECTIVE DVORAK ESTIMATES AND AUTOMATED FIXES LISTED BELOW. INITIAL WIND RADII BASIS: 061025Z METOP-B ASCAT PASS CURRENT STEERING MECHANISM: BUILDING RIDGING TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS RCTP: T3.0 - 45 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 48 KTS AT 061200Z CIMSS ADT: 37 KTS AT 061200Z CIMSS AIDT: 39 KTS AT 061200Z CIMSS D-MINT: 43 KTS AT 060748Z CIMSS D-PRINT: 52 KTS AT 061200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 KTS SST: 26-27 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: PERSISTENT AND SIGNIFICANT DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 04W IS PROJECTED TO TRACK NORTH-NORTHWESTWARD UNDER THE INFLUENCE OF A STRENGTHENING SUBTROPICAL RIDGE TO THE EAST. AROUND TAU 24, THE SYSTEM IS EXPECTED TO BEGIN TURNING NORTHEASTWARD, AS IT ROUNDS THE PERIPHERY OF THE RIDGE AND BECOMES EMBEDDED WITHIN MID-LATITUDE DEEP-LAYER WESTERLY FLOW SHORTLY AFTERWARD. SUBTROPICAL TRANSITION IS ANTICIPATED TO INITIATE NEAR TAU 36, WITH COMPLETION LIKELY BY TAU 48. IN TERMS OF THERMODYNAMIC AND DYNAMIC SUPPORT, THE SYSTEM CURRENTLY RESIDES IN A MARGINALLY UNFAVORABLE ENVIRONMENT THAT IS FORECAST TO BECOME INCREASINGLY HOSTILE. VERTICAL WIND SHEAR IS EXPECTED TO INCREASE BEYOND 30 KTS WITHIN 6 TO 12 HOURS, WITH DRY MID TO UPPER TROPOSPHERIC AIR COMPLETELY ENGULFING THE SYSTEM WITHIN THE NEXT 36 HOURS. CONCURRENTLY, SST ARE FORECAST TO DECLINE BELOW 20 C BY THE END OF THE FORECAST PERIOD, COLLECTIVELY RESULTING IN A STEADY WEAKENING TREND THROUGH THE FORECAST PERIOD. MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN STRONG CONSENSUS THROUGH TAU 24, WITH ENSEMBLE AND DETERMINISTIC MODEL SPREADS CONFINED TO A CROSS-TRACK SPREAD OF 70 NM. BEYOND THIS PERIOD, FORECAST DIVERGENCE INCREASES DUE TO VARYING REPRESENTATIONS OF THE SYSTEM INTERACTING WITH THE BAROCLINIC ZONE AND ASSOCIATED UPPER-LEVEL FLOW. NAVGEM SOLUTION SUGGESTS A MORE RAPID AND TIGHTER RECURVATURE, WHILE ECMWF ENSEMBLE AND GFS DETERMINISTIC MODEL DEPICT A MORE GRADUAL AND BROADER TURN TOWARD THE NORTHEAST. THE OFFICIAL JTWC FORECAST TRACK LIES NEAR THE MULTI-MODEL CONSENSUS AND IS CARRIED WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ACROSS ALL CONSENSUS MEMBERS, SUPPORTING A FORECAST OF PROGRESSIVE WEAKENING. ACCORDINGLY, THE JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE THROUGH TAU 48. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH// NNNN