WDPN33 PGTW 282100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 23.9N 131.7E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 263 NM SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT, CONSOLIDATING SYSTEM WITH A CENTRAL DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 281725Z AMSR2 37GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS A SMALL MICROWAVE EYE FEATURE WITH A CYAN RING, WHICH TYPICALLY INDICATES IMMINENT RAPID INTENSIFICATION (RI). ANIMATED WATER VAPOR IMAGERY DEPICTS ROBUST POLEWARD OUTFLOW WITH TRANSVERSE BANDING ALONG THE WESTERN AND NORTHERN SEMICIRCLES. ADDITIONALLY, LOW VERTICAL WIND SHEAR AND WARM SST VALUES (28-29C) SUPPORT FURTHER INTENSIFICATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AMSR2 IMAGE. THE INITIAL INTENSITY OF 45 KTS IS HEDGED ABOVE THE DVORAK INTENSITY ESTIMATES, WHICH ARE TOO LOW DUE TO THE COMPACT SYSTEM SIZE. ADT ESTIMATES HAVE INCREASED STEADILY FROM 43 KNOTS AT 281740Z TO THE 281950Z ESTIMATE OF 49 KNOTS. THE ADT RAW T NUMBER IS AT 3.6 (ABOUT 55 KNOTS). INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.5 - 35 KTS CIMSS ADT: 43 KTS AT 281740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: PEAK INTENSITY IS HIGHER AT 70 KNOTS WITH INCREASING POTENTIAL FOR RAPID INTENSIFICATION OVER THE NEXT 36 HOURS. FORECAST DISCUSSION: TS 20W IS A COMPACT SYSTEM WITH A CDO AND A MICROWAVE EYE FEATURE AND APPEARS TO BE RAPIDLY CONSOLIDATING UNDER HIGHLY FAVORABLE CONDITIONS INCLUDING ROBUST POLEWARD OUTFLOW. THEREFORE, THE SYSTEM IS FORECAST TO INTENSIFY TO A PEAK OF 70 KNOTS WITHIN THE NEXT 36 HOURS AS IT ROUNDS THE STR AXIS. AFTER TAU 36, TS 20W SHOULD ENCOUNTER MIDLATITUDE WESTERLIES AS IT TRACKS ALONG THE NORTHWESTERN PERIPHERY OF THE STR WITH CONVERGENCE ALOFT LEADING TO A STEADY WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST PERIOD. AFTER TAU 72, THE SYSTEM IS EXPECTED TO SLOW AND STALL AS A LOW-LEVEL HIGH BUILDS TO THE NORTH AND NORTHEAST EFFECTIVELY BLOCKING ANY FURTHER POLEWARD PROGRESSION. TS 20W WILL WEAKEN SIGNIFICANTLY DUE TO THE UPPER-LEVEL CONVERGENCE AND BAROCLINIC INTERACTION DURING THE EXTENDED PERIOD. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 48 WITH AN 110NM SPREAD IN SOLUTIONS. HOWEVER, THE GUIDANCE DIVERGES QUICKLY WITH THE BULK OF THE GUIDANCE INDICATING A QUASI-STATIONARY OR SLOW TRACK THROUGH TAU 120. SOME MODELS INDICATE A FAST NORTHEASTWARD TRACK INCLUDING NAVGEM, AFUM, AEMN AND UEMN. EXAMINATION OF NAVGEM FIELDS INDICATES A QUASI-STATIONARY PHASE SOUTH-SOUTHEAST OF TOKYO, HOWEVER, THE VORTEX TRACKER IS JUMPING ERRONEOUSLY NORTHEASTWARD TO OTHER DISTURBANCES. THE 281200Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) BOTH SHOW THE LARGE MAJORITY OF SOLUTIONS STALLING THE SYSTEM SOUTH OF HONSHU; VERY FEW SOLUTIONS INDICATE A RECURVE SCENARIO. THE TRACK CONFIDENCE AFTER TAU 72 IS DUE PRIMARILY TO UNCERTAINTY IN THE EXACT TRACK ONCE THE SYSTEM SLOWS AND STALLS. THE 281200Z COAMPS-TC ENSEMBLE INDICATES A 60 TO 80 PERCENT PEAK PROBABILITY OF RI THROUGH TAU 36 SUPPORTING THE JTWC INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN