WDPN31 PGTW 060900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 019// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.7N 149.4E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 481 NM EAST-SOUTHEAST OF NARITA AIRPORT MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL STORM (TS) 04W (MUN) WITH WELL DEFINED, BUT SHALLOW CONVECTIVE SPIRAL BANDS. THE SYSTEM IS STRUGGLING TO SUSTAIN DEEP CONVECTION DUE TO SIGNIFICANT DRY AIR ENTRAINMENT, BUT MANAGES TO MAINTAIN STRUCTURALLY SOUND LOW- LEVEL VORTEX AT THE MOMENT. ADDITIONAL ENVIRONMENTAL ANALYSIS REVEALS BORDERLINE WARM (26-27 C) SEA SURFACE TEMPERATURES (SST), LOW (5-10 KTS) VERTICAL WIND SHEAR AND MODERATE, PRIMARILY EQUATORWARD UPPER LEVEL OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE LLCC LOCATION PRESENT IN VISIBLE SATELLITE IMAGERY, AS WELL AS EXTRAPOLATION FROM A 060316Z GCOMW1 AMSR2 37 GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND AUTOMATED FIXES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: RIDGING TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.0 - 45 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 53 KTS AT 060530Z CIMSS ADT: 34 KTS AT 060530Z CIMSS AIDT: 42 KTS AT 060530Z CIMSS D-MINT: 48 KTS AT 060551Z CIMSS D-PRINT: 49 KTS AT 060600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 10-15 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: LOW 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 TRACK NORTHWARD IN RESPONSE TO CONTINUOUSLY BUILDING RIDGING TO THE EAST OF THE SYSTEM. AS A RESULT, AFTER TAU 12, THE SYSTEM WILL SHIFT TOWARD THE NORTHWEST. BETWEEN TAUS 24 AND 36, TS MUN IS EXPECTED TO ROUND THE AXIS OF THE RIDGE AND BEGIN TRANSITING NORTHEASTWARD, WHILE EVENTUALLY BECOMING EMBEDDED IN A DEEP-LAYER WESTERLY FLOW. THE SYSTEM IS FORECAST TO BEGIN ITS SUBTROPICAL TRANSITION AROUND TAU 36, WITH COMPLETION EXPECTED BY TAU 48. IN REGARD TO INTENSITY, TS 04W IS CURRENTLY IN A MARGINAL ENVIRONMENT, WHICH IS SOON EXPECTED TO BECOME INCREASINGLY HOSTILE. WHILE VWS IS EXPECTED TO INCREASE TO OVER 30 KTS BY TAU 12, THE SYSTEM IS EXPECTED TO BE COMPLETELY SURROUNDED BY DRY AIR WITHIN THE NEXT 36 HOURS. ADDITIONALLY, SST WILL DROP TO BELOW 20 C BEFORE THE END OF THE FORECAST PERIOD, RESULTING IN STEADY WEAKENING OF THE STORM. MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE NEXT 24 HOURS, AS WITNESSED BY A CROSS-TRACK SPREAD OF 50 NM AT TAU 24. HOWEVER UNCERTAINTY INCREASES AFTERWARDS, DRIVEN BY DIFFERENCES IN UPPER-LEVEL ENVIRONMENT INTERACTION ASSESSMENT BY THE MODELS. WHILE NAVGEM AND JGSM PREDICT A TIGHTER AND QUICKER TURN, OTHER MODELS LIKE EMCWF AND ECMWF ENSEMBLE PREDICT A WIDER AND SLOWER TURN TOWARD THE NORTHEAST. JTWC TRACK FORECAST IS LAID CLOSE TO THE CONSENSUS WITH MEDIUM CONFIDENCE. IN TERMS OF INTENSITY, JTWC FORECAST IS ASSESSED WITH HIGH CONFIDENCE DRIVEN BY TIGHT AGREEMENT AMONG ALL CONSENSUS MEMBER, INDICATING STEADY WEAKENING THROUGH TAU 48. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH// NNNN