WDPN31 PGTW 251500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (MINDULLE) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.1N 137.4E INITIAL INTENSITY: 115 KTS GEOGRAPHIC REFERENCE: 457 NM SOUTH-SOUTHWEST OF IWO TO MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 38 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TYPHOON 20W HAS UNDERGONE A SHORT PERIOD OF RAPID INTENSIFICATION OVER THE PAST SIX HOURS, WITH THE APPEARANCE OF A WELL DEFINED BUT VERY SMALL EYE IN THE EIR IMAGERY. HOWEVER, SUBSEQUENT ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM STRUGGLING TO MAINTAIN THE EYE AND EYEWALL STRUCTURE, PARTICULARLY ON THE NORTHWEST SIDE, WITH THE EYE WINKING IN AND OUT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE EVIDENT AT THE 1200Z HOUR. THE INITIAL INTENSITY OF 115 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, ON THE HIGH END OF AGENCY CURRENT INTENSITY ESTIMATES FROM PGTW AND KNES. WHILE THE SATCON HAS COME UP TO A MORE REALISTIC 91 KNOTS, THE ADT STILL REFUSES TO ACKNOWLEDGE THE PRESENCE OF THE EYE, AND THUS LAGS THE REMAINDER OF THE INTENSITY ESTIMATES TO A MASSIVE DEGREE. A 250821Z SMAP FIX OF 107 KNOTS (1-MIN CONVERSION), PRIOR TO DEVELOPMENT OF A SOLID AND DEFINED EYE FEATURE, PROVIDED ADDITIONAL SUPPORT TO THE INITIAL INTENSITY. OVERALL, THE ENVIRONMENT REMAINS FAVORABLE WITH LOW VWS AND STRONG POLEWARD AND EQUATORWARD OUTFLOW. THE OUTFLOW IN THE NORTHWEST SECTOR HOWEVER IS BEING IMPINGED UPON BY SOME NORTHWESTERLY FLOW ALOFT, WHICH MAY ALSO BE ENTRAINING SOME MID-LEVEL DRY AIR INTO THE WEST SIDE OF THE SYSTEM. SSTS REMAIN WARM (30C) AND OHC LEVELS HIGH FOR NOW, BUT THE SYSTEM WILL SHORTLY MOVE OVER A COLD EDDY WITH RELATIVELY LOW OHC, WHICH LIES ALONG THE FORECAST TRACK. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN BETWEEN AN EAST-WEST ORIENTED EXTENSION OF THE STR LYING ALONG THE 30N LATITUDE, AND A DEVELOPING STR CENTERED NEAR GUAM. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T5.5 - 102 KTS RCTP: T5.5 - 102 KTS KNES: T6.0 - 115 KTS CIMSS SATCON: 91 KTS AT 250902Z CIMSS ADT: 59 KTS AT 251140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD OTHER FACTORS: IMPINGING NORTHWESTERLY FLOW REDUCING OUTFLOW IN THE NORTHWEST SECTOR. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: TYPHOON 20W IS FORECAST TO CONTINUE TRACKING SLOWLY NORTHWESTWARD THROUGH TAU 48, IN A COMPETING STEERING ENVIRONMENT. THE STRENGTHENING STR CENTERED NEAR GUAM IS CREATING A TIGHTENING GRADIENT ON THE SOUTHEAST SIDE OF THE CIRCULATION, TENDING TO PUSH THE SYSTEM TO THE NORTH. HOWEVER, THE RIDGE EXTENDING EAST FROM THE STR CENTERED NEAR SHANGHAI IS BLOCKING MUCH IN THE WAY OF POLEWARD MOVEMENT FOR THE TIME BEING. THE NET RESULT WILL BE A SLOW DRIFT TO THE NORTHWEST THROUGH ABOUT TAU 36, WITH THE POSSIBILITY OF SHORT PERIOD OF QUASI-STATIONARY MOTION IN THE NEXT 24 HOURS. A SERIES OF MID-LATITUDE TROUGHS TRANSITING TO THE NORTH WILL ERODE THE NORTHERN RIDGE, SUCH THAT BY TAU 48, THE PRIMARY STEERING MECHANISM WILL SHIFT TO THE STRONG STR TO THE EAST. TY 20W WILL EJECT NORTHWARD AFTER TAU 48, THEN TURN NORTHEASTWARD AND ACCELERATE TO THE SOUTHEAST OF HONSHU, NOT ROUNDING THE RIDGE AXIS AS MUCH AS TURNING NORTHEAST AHEAD OF AN APPROACHING DEEP MID-LATITUDE TROUGH. THE SYSTEM HAS ABOUT ANOTHER 12 TO 24 HOURS TO FURTHER INTENSIFY BEFORE IT MOVES OVER THE COLD EDDY IN ITS PATH. THE SLOW FORWARD TRACK SPEEDS WILL ONLY SERVE TO ACCENTUATE THE UPWELLING OF COOLER WATERS, WHICH WILL SERVE TO PUT A BRAKE ON INTENSIFICATION AFTER TAU 24. IN THE NEAR-TERM, THE SYSTEM SHOULD BE ABLE TO PUSH BACK THE WEAK NORTHWESTERLY FLOW CURRENTLY IMPINGING ON THE NORTHWEST SIDE OF THE SYSTEM, AND IMPROVE THE OVERALL OUTFLOW. THE SYSTEM IS EXPECTED TO PEAK AT 130 KNOTS AT TAU 24. THEN THE SYSTEM WILL STEADILY WEAKEN AS IT STRUGGLES AGAINST DECREASED OHC, DECREASED OUTFLOW ALOFT AND INCREASING MID-LEVEL SHEAR. ONCE THE SYSTEM STARTS TO ACCELERATE TO THE NORTHEAST, SSTS REMAIN HIGH ENOUGH TO SUPPORT A BRIEF PERIOD OF STEADY INTENSITY TO TAU 96 AS THE SYSTEM ONCE AGAIN TAPS INTO ROBUST POLEWARD OUTFLOW INTO THE BASE OF A STRONG MID-LATITUDE TROUGH, BUT BY TAU 96 INCREASING SHEAR WILL BEGIN TO TAKE A TOLL, AND THE SYSTEM WILL BEGIN TO WEAKEN ONCE MORE. MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN MODERATE AGREEMENT, WITH 155 NM SPREAD AT TAU 72 BETWEEN THE ECMWF ENSEMBLE ON THE LEFT AND JGSM ON THE RIGHT. CROSS-TRACK SPREAD INCREASES TO A MODEST 210 NM BY TAU 120, BUT ALONG TRACK SPREAD INCREASES DRAMATICALLY AFTER TAU 96, UP TO 400 NM BY TAU 120. THE DUE TO THE UNCERTAINTY IN THE TIMING OF THE EROSION OF THE BLOCKING RIDGE TO THE NORTH AND THE EJECTION OF TY 20W TO THE NORTH, AND THE SUBSEQUENT TIMING OF THE RECURVE AND ACCELERATION TO THE NORTHEAST, THERE IS OVERALL LOW CONFIDENCE IN THE TRACK FORECAST. INTENSITY GUIDANCE REMAINS MIXED, WITH RIPA STILL BEING TRIGGERED AND THE SHIPS GUIDANCE INDICATING ADDITIONAL INTENSIFICATION TO 135 KNOTS OR HIGHER. THE COAMPS-TC, HWRF AND GFS MEANWHILE INDICATE EITHER IMMEDIATE WEAKENING OR WEAKENING AFTER A SHORT INCREASE TO TAU 12. THE JTWC FORECAST LIES ABOVE THE CONSENSUS MEAN, BUT BELOW THE SHIPS AND RIPA GUIDANCE WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN