WDPN31 PGTW 060300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 018// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.2N 149.1E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 504 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM (TS) 04W (MUN) WITH SHALLOW CONVECTION ENCIRCLING A WELL-DEFINED, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). A 052203Z GMI 89 GHZ MICROWAVE IMAGE REVEALS THE WEAK NATURE OF THE CONVECTION AND THE EXPOSED LOW-LEVEL CLOUD LINES WITHIN THE CENTER OF THE CIRCULATION. ENVIRONMENTAL ANALYSIS INDICATES THAT 04W IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD AND EQUATORWARD OUTFLOW, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARMISH (26-27 C) SEA SURFACE TEMPERATURES GREATLY OFFSET BY SIGNIFICANT AMOUNTS OF DRY AIR BEING ENTRAINED INTO THE CORE OF THE VORTEX. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION FROM THE MENTIONED GMI MICROWAVE IMAGE AND THE PARTIALLY EXPOSED LLCC IN ANIMATED MSI. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ADDITIONALLY, A 052006Z RCM-1 SAR IMAGE HAD A VMAX OF 53 KTS, FURTHER SUPPORTING THE INITIAL INTENSITY AND WIND RADII ASSESSMENTS. INITIAL WIND RADII BASIS: 052006Z RCM-1 SAR DATA CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSION OF RIDGING TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS RCTP: T2.5 - 35 KTS KNES: T4.0 - 65 KTS CIMSS ADT: 35 KTS AT 060000Z CIMSS AIDT: 46 KTS AT 060000Z CIMSS DPRINT: 48 KTS AT 060000Z CIMSS DMINT: 50 KTS AT 052203Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 5-10 KTS SST: 26-27 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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 FORECAST TO BEGIN TURNING NORTHWARD AS RIDGING TO THE EAST BUILDS IN NEXT TO THE VORTEX. A NORTHWARD TRACK IS FORECAST TO CONTINUE THOUGH TAU 24 BEFORE A TURN BACK TO THE NORTH-NORTHWEST BEGINS, IN RESPONSE TO THE FURTHER DEVELOPMENT OF THE RIDGE. 04W IS THEN FORECAST TO ROUND THE RIDGE AXIS NEAR TAU 48 AND ACCELERATE TO THE NORTHEAST THROUGH TAU 72. SUBTROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 48 AND BE COMPLETE NO LATER THAN TAU 72 AS THE VORTEX ENTERS COOLER WATERS AND BECOMES COMPLETELY ENGULFED BY DRY AIR. 04W IS FORECAST TO MAINTAIN INTENSITY THROUGH TAU 24 AS SEA SURFACE TEMPERATURES REMAIN RELATIVELY WARM AND SHEAR REMAINS LOW. AFTER TAU 24, THESE FACTORS BEGIN TO SIGNIFICANTLY WORSEN, CAUSING WEAKENING THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. SHEAR IS EXPECTED TO INCREASE TO AROUND 30 KTS NEAR TAU 36 AND THEN SEA SURFACE TEMPERATURES DROP BELOW 24 C NEAR TAU 48. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT WITH A 149 NM CROSS-TRACK SPREAD AT TAU 48. AFTER TAU 48, MODELS DIVERGE DUE TO DIFFERENCES IN HOW THE SHALLOW VORTEX INTERACTS WITH THE UPPER-LEVEL ENVIRONMENT. NAVGEM AND GALWEM BOTH RACE THE VORTEX OFF TO THE NORTHEAST AFTER TAU 48 WHILE THE REMAINDER OF GUIDANCE SUGGEST A SLOWER TURN TO THE NORTHEAST. THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE, CLOSE TO THE CONSENSUS THROUGH TAU 48 AND SLOWER THROUGH TAU 72. INTENSITY GUIDANCE NOW AGREES ON A STEADY INTENSITY THROUGH TAU 12 AND THEN WEAKENING THEREAFTER. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN