WDPN31 PGTW 042100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.7N 146.0E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 420 NM SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL STORM (TS) 04W (MUN) WITH DISORGANIZED CONVECTIVE BURSTS OBSCURING A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A 041532Z AMSR2 89 GHZ MICROWAVE IMAGE SHOWS THE EXPOSED LOW-LEVEL CLOUDS TIGHTLY WRAPPING INTO THE CENTER WITH DEEP CONVECTION CONFINED TO THE NORTHERN SECTOR. ENVIRONMENTAL ANALYSIS INDICATES THAT 04W IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY ROBUST POLEWARD OUTFLOW, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES, SLIGHTLY OFFSET BY DRY AIR WITHIN THE SOUTHERN PORTION OF THE VORTEX. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM THE MENTIONED AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE TO THE SOUTH AND SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 45 KTS AT 041528Z CIMSS ADT: 39 KTS AT 041800Z CIMSS AIDT: 56 KTS AT 041800Z CIMSS DPRINT: 37 KTS AT 041800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: DRY AIR ENTRAINMENT WITHIN THE SOUTHERN SEMICIRCLE 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: 04W IS FORECAST TO TRACK EAST-NORTHEASTWARD THROUGH TAU BEFORE MAKING A TURN NORTHWARD AS RIDGING BUILDS IN TO THE EAST OF THE SYSTEM. 04W WILL THEN CONTINUE ON A GENERALLY NORTHWARD TRACK THROUGH TAU 72, ALONG THE WESTERN PERIPHERY OF THE RIDGE EXTENSION. AFTER TAU 72, THE SYSTEM IS FORECAST TO ROUND THE RIDGE AXIS AND TURN TOWARD THE NORTHEAST. SUBTROPICAL TRANSITION WILL BEGIN AROUND TAU 72 AND COMPLETE BY TAU 96 AS THE VORTEX SHALLOWS, BECOMES ENGULFED BY DRY AIR, AND ENTERS VERY COLD OCEAN TEMPERATURES. REGARDING INTENSITY, 04W IS FORECAST TO INTENSIFY OVER THE NEXT 24 HOURS TO A PEAK OF 65 KTS AS POLEWARD OUTFLOW REMAINS ROBUST AND SHEAR REMAINS LOW. AFTER TAU 24, SEA SURFACE TEMPERATURES WILL BEGIN TO DROP AND SHEAR WILL BEGIN TO RISE AS THE VORTEX GAINS LATITUDE, CAUSING A WEAKENING TREND TO PERSIST THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT WITH A 169 NM CROSS-TRACK SPREAD AT TAU 72. AFTER TAU 72, ALONG-TRACK SPREAD BEGINS TO INCREASE DUE TO DIFFERING INTERACTIONS WITH THE UPPER-LEVEL ENVIRONMENT. THE JTWC TRACK FORECAST IS PLACED WITH OVERALL MEDIUM CONFIDENCE THROUGHOUT THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH ALL MODELS DEPICTING INTENSIFICATION THROUGH TAU 24 AND WEAKENING THEREAFTER. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE AS WELL. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN