WDPN31 PGTW 041500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.2N 145.3E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 247 NM NORTHEAST OF CHICHI JIMA MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 25 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 04W HAS MAINTAINED ROBUST EASTWARD OUTFLOW, ENHANCED BY A JET AND TUTT CELL TO THE EAST. THE SYSTEM HAS DEVELOPED LIMITED OUTFLOW OVER THE CORE, WITH PERSISTENT DEEP CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED ENHANCED INFRARED SATELLITE IMAGERY, WHICH DEPICTS A COMPACT CENTRAL DENSE OVERCAST FEATURE AND PARTIALLY EXPOSED LLCC OVER THE SOUTHWESTERN QUADRANT. THE INITIAL POSITION IS ALSO SUPPORTED BY A FORTUITOUS 040811Z RCM-1 SAR IMAGE, WHICH SHOWS A WELL-DEFINED CENTER. THE INITIAL INTENSITY REMAINS ASSESSED AT 55 KNOTS BASED ON THE RCM-1 DATA, WHICH INDICATED A VMAX OF 54 KNOTS AND THE CIMSS AIDT ESTIMATE OF 54 KNOTS. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T2.5 - 35 KTS RCTP: T2.5 - 35 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 46 KTS AT 041133Z CIMSS ADT: 37 KTS AT 041130Z CIMSS AIDT: 54 KTS AT 041130Z CIMSS D-PRINT: 43 KTS AT 041150Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 25-26 CELSIUS OUTFLOW: STRONG EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 04W IS EMBEDDED WITHIN A REVERSE TROUGH FORMATION, WITH THE SUBTROPICAL STEERING RIDGE EXTENDING FROM THE PHILIPPINES NORTHEASTWARD TO THE EASTERN PERIPHERY OF THE SYSTEM. THIS IS GENERAL STEERING PATTERN WILL STEER THE SYSTEM NORTHEASTWARD THROUGH TAU 36 TOWARD A BREAK IN THE STR ASSOCIATED WITH AN UPPER- LEVEL SHORTWAVE TROUGH. MODEST INTENSIFICATION IS EXPECTED DUE TO MARGINAL SST VALUES (24-25C) AND ROBUST OUTFLOW, WITH A PEAK INTENSITY OF 70 KNOTS EXPECTED BY TAU 24. AFTER TAU 36, THE TROUGH WILL PROPAGATE EASTWARD AND THE STR WILL REBUILD TO THE NORTH, WHICH WILL RESULT IN A MORE NORTHWARD TRACK THROUGH TAU 96. AFTER TAU 96, THE SYSTEM WILL ROUND THE STR AXIS AND ENCOUNTER SUBTROPICAL WESTERLIES. RAPID WEAKENING WILL OCCUR THROUGH THE REMAINDER OF THE PERIOD DUE TO COLD SST VALUES AND HIGH (25-40 KNOTS) VERTICAL WIND SHEAR. MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 36 BUT DIVERGES QUICKLY THROUGH TAU 120. WITH THE EXCEPTION OF NAVGEM, THE SOLE OUTLIER, THE DETERMINISTIC MODELS HAVE COME INTO BETTER AGREEMENT, WITH GFS NOW SHIFTING SIGNIFICANTLY CLOSER TO THE BULK OF THE GUIDANCE. THE 040600Z GEFS ENSEMBLE CONTINUES TO INDICATE A WIDE SPREAD OF SOLUTIONS, WITH THE BULK OF THE GUIDANCE WELL EAST OF JAPAN. THE ECENS ENSEMBLE REMAINS IN TIGHTER AGREEMENT AND SUPPORTS THE JTWC TRACK FORECAST WITH MEDIUM OVERALL CONFIDENCE. RELIABLE INTENSITY GUIDANCE INDICATES A PEAK INTENSITY NEAR TAU 24 BUT VARIES SIGNIFICANTLY FROM 58 TO 76 KNOTS. THIS REFLECTS THE UNCERTAINTY IN THE JTWC INTENSITY FORECAST, WITH MEDIUM OVERALL CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN