WDPN31 PGTW 260900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 20W (MINDULLE) WARNING NR 016// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.8N 136.7E INITIAL INTENSITY: 145 KTS GEOGRAPHIC REFERENCE: 442 NM SOUTHWEST OF IWO TO MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 48 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES SUPER TYPHOON MINDULLE HAS MAINTAINED A 20-NM WIDE STADIUM EYE WITH VERY WARM (21C) EYE TEMPERATURES OVER THE PAST SIX HOURS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE. SUBSEQUENT MSI FRAMES SUGGEST THE SYSTEM HAS BECOME QUASI-STATIONARY, EVEN WOBBLING A BIT TO THE EAST. A 250421Z AMSR2 COMPOSITE 36GHZ IMAGE DEPICTED A SOLID INNER EYEWALL OF INTENSE CONVECTION, WITH A SECONDARY EYEWALL BEGINNING TO FORM ABOUT 40 NM FROM THE CENTER, SEEMINGLY CONFIRMING THE M-PERC EYEWALL REPLACEMENT CYCLE (ERC) PREDICTION AID, WHICH INDICATED A HIGH PROBABILITY (OVER 90 PERCENT) OF AN IMMINENT ERC. THE INITIAL INTENSITY IS INCREASED SLIGHTLY TO 145 KNOTS WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY ABOVE THE T7.0 CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES, HEDGED UPWARD IN LIGHT OF THE VERY WARM EYE TEMPERATURE, INDICATING THAT DVORAK ESTIMATES ARE VERY POSSIBLY TOO LOW. OBJECTIVE ESTIMATES CONTINUE TO LAG BEHIND THE AGENCY FIXES BUT HAVE CLOSED THE GAP OVER THE PAST FEW HOURS. THE STORM HAS LIKELY PEAKED IN INTENSITY AS LOOKS TO BEGIN AN ERC AND SLOWLY MOVES OVER AN AREA OF LOWER OHC WATERS. THE ENVIRONMENT OTHERWISE REMAINS VERY FAVORABLE, THOUGH OUTFLOW IS SOMEWHAT LIMITED TO THE NORTHWEST DUE TO SOME NORTHEASTERLY FLOW 300 NM TO THE WEST OF THE CORE. OUTFLOW ELSEWHERE REMAINS STRONGLY RADIAL, TURNING ANTICYCLONICALLY INTO THE BASE OF 200 MB TROUGH TO THE NORTHEAST. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT BETWEEN AND EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED NEAR SHANGHAI EXTENDING EAST ALONG 30N TO 140E, AND A DEVELOPING STR CENTERED TO THE EAST-SOUTHEAST NEAR GUAM. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T7.0 - 140 KTS RJTD: T7.0 - 140 KTS RCTP: T7.0 - 140 KTS KNES: T7.0 - 140 KTS CIMSS SATCON: 133 KTS AT 260435Z CIMSS ADT: 129 KTS AT 260540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG RADIAL OTHER FACTORS: OUTFLOW LIMITED TO THE NORTHWEST. SYSTEM IS ENTERING AN POOL OF LOW OHC. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: SUPER TYPHOON 20W IS FORECAST TO DRIFT SLOWLY NORTHWARD OVER THE NEXT 24 TO 36 HOURS, CAUGHT IN THE CLUTCHES OF TWO COMPETING STEERING INFLUENCES. A STR CENTERED TO THE SOUTHEAST IS CURRENTLY BUILDING AND WHILE THE STRENGTHENING GRADIENT TO THE SOUTHEAST WOULD SUGGEST A PUSH NORTHWARD, THIS MOTION IS CURRENTLY BLOCKED BY THE PRESENCE OF A STRONG EAST-WEST ORIENTED RIDGE ALONG THE 30N LATITUDE. UNTIL SUCH TIME AS THIS RIDGE BREAKS DOWN, STY 20W IS EFFECTIVELY STUCK IN THE VICINITY OF ITS CURRENT POSITION. TRACK SPEEDS ARE EXPECTED TO BE THREE KNOTS OR LESS, AND THE MOST RECENT IMAGERY LOOPS SUGGEST THE SYSTEM HAS ALREADY BECOME QUASI-STATIONARY. BY TAU 36, THE PASSAGE OF A SUCCESSION OF MID-LATITUDE TROUGHS IS EXPECTED TO SLOWLY ERODE THE RIDGE TO THE NORTH WHILE THE RIDGE TO THE EAST DEVELOPS INTO A HIGH AMPLITUDE NORTH-SOUTH ORIENTATION, ALLOWING STY 20W TO ESCAPE THE WEAK STEERING ENVIRONMENT AND BEGIN TRACKING NORTHWESTWARD. THE SYSTEM IS EXPECTED TO ACCELERATE NORTHEASTWARD AFTER TAU 72 ALONG THE ENHANCED GRADIENT BETWEEN THE HIGH AMPLITUDE RIDGE TO THE EAST AND AN APPROACHING MID-LATITUDE TROUGH MOVING IN FROM THE WEST. THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 120 AS IT MOVES EAST OF TOKYO. STY 20W HAS LIKELY REACHED ITS PEAK INTENSITY, AND IS EXPECTED TO BEGIN AN ERC IMMINENTLY, LEADING TO A NEAR-TERM WEAKENING AS THE EYEWALL WEAKENS, EXPANDS AND BECOMES REESTABLISHED. HOWEVER, DUE TO THE SLOW FORWARD MOTION OVER RELATIVELY LOW OHC WATERS, IT IS NOT EXPECTED THAT THE SYSTEM WILL REINTENSIFY AFTER COMPLETION OF ERC, MORE LIKELY MAINTAINING ITS WEAKENED STATE. THE SYSTEM IS EXPECTED TO MAINTAIN STEADY STATE OR WEAKEN SLIGHTLY AFTER TAU 24 AS IT STRUGGLES TO OBTAIN THE NECESSARY ENERGY FROM THE LOW OHC WATERS. THE RATE OF WEAKENING WILL ACCELERATE AFTER TAU 72 AS THE SYSTEM ENCOUNTERS INCREASING MID-LEVEL SHEAR AND ENTRAINMENT OF DRY AIR FROM THE WEST. BY TAU 96 THE SYSTEM ENCOUNTERS SOME CONVERGENT FLOW ALOFT WHICH WILL SERVE TO FURTHER ACCELERATE THE PACE OF WEAKENING. AS THE SYSTEM MOVES NORTH THE WIND FIELD IS EXPECTED TO DRAMATICALLY INCREASE, AND WHILE THE CENTER IS EXPECTED TO REMAIN WELL OFFSHORE, GALE FORCE WINDS ARE EXPECTED OVER A SIGNIFICANT PORTION OF EASTERN HONSHU, AND STORM FORCE WINDS ARE A POSSIBILITY NEAR THE TOKYO METRO AREA EASTWARD. MODEL DISCUSSION: TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT OVERALL IN TERMS OF BOTH CROSS AND ALONG-TRACK SPREAD. CROSS-TRACK SPREAD IS 185 NM AT BOTH TAU 72 AND 120 WITH THE ENVELOPE DEFINED BY NAVGEM ON THE WEST AND THE GFS ENSEMBLE MEAN ON THE RIGHT. ALONG-TRACK SPREAD UNSURPRISINGLY INCREASES AFTER RECURVATURE TO A MODEST 250 NM AT TAU 120. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, SLIGHTLY WEST AND SLOWER THAN THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN FAIRLY GOOD AGREEMENT, ALL MODELS EXCEPT THE SHIPS GUIDANCE SUGGESTING A NEAR-TERM DECREASE IN INTENSITY, LEVELING OFF AFTER TAU 36. THE JTWC FORECAST CLOSELY TRACKS THE HWRF SOLUTION TO TAU 12, THEN LEVELS OFF ABOUT 15 KNOTS HIGHER THAN THE CONSENSUS MEAN THROUGH THE REMAINDER OF THE FORECAST. UNCERTAINTY SURROUNDING THE TIMING AND IMPACT OF THE ERC AND THUS THE LONGER RANGE FORECAST, ARGUES FOR MEDIUM TO LOW CONFIDENCE IN THE INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN