WDPN31 PGTW 231500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 021// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 22.6N 139.4E INITIAL INTENSITY: 110 KTS GEOGRAPHIC REFERENCE: 675 NM EAST-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS SIGNIFICANT WAVE HEIGHT: 46 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE CORE OF TYPHOON 17W (SAUDEL) CONTINUING TO REORIENT AS THE SYSTEM CONTINUES TO UNDERGO AN EYEWALL REPLACEMENT CYCLE (ERC). THE MOST RECENT HIGH RESOLUTION MICROWAVE IMAGERY OVER THE SYSTEM WAS A 230811Z WSFM 37 GHZ IMAGE, WHICH SHOWED THE INNER EYEWALL CONTINUING TO ERODE AND BEING SURROUNDED BY THE MORE DOMINANT OUTER EYEWALL. THE LACK OF MORE RECENT MICROWAVE IMAGERY CAUSES THERE TO BE SOME UNCERTAINTY IN THE PROGRESSION OF THE ERC. THE EIR DOES SHOW A DISTINCT WEAKNESS IN THE NORTHWESTERN QUADRANT OF THE EYEWALL, INDICATING THAT THE INNER EYEWALL IS LIKELY BEING CHOKED OFF AND ERODING IN THE LATER STAGES OF THE ERC TIMELINE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN ANIMATED EIR AND SUPPORTED BY A TIMELY 231143Z METOP-B ASCAT PASS. THE INITIAL 34 AND 50 KT WIND RADII ARE PLACED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA. THE INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 17W REMAINS PLACED WITHIN A FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG RADIAL OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: 231143Z METOP-B ASCAT SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF AN ELONGATED SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T5.5 - 102 KTS RCTP: T6.0 - 115 KTS KNES: T5.0 - 90 KTS CIMSS ADT: 104 KTS AT 231200Z CIMSS AIDT: 103 KTS AT 231200Z CIMSS D-PRINT: 101 KTS AT 231200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG RADIAL OTHER FACTORS: ONGOING EYEWALL REPLACEMENT CYCLE ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 17W IS FORECAST TO CONTINUE TRACKING WEST- NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO THE NORTHEAST THROUGH TAU 12. NEAR TAU 12, THE STR IS EXPECTED TO MERGE WITH A SEPARATE STR CENTERED OVER SOUTHERN JAPAN, WHICH WILL KEEP 17W ON A WEST-NORTHWESTWARD TRAJECTORY THROUGH TAU 60. THE SYSTEM IS FORECAST TO SKIRT THE NORTHERN COAST OF OKINAWA BETWEEN TAU 48 AND 60. AFTER TAU 60, TRACK SPEEDS ARE EXPECTED TO SLOW THROUGH TAU 96 AS THE SYSTEM ENTERS A WEAKNESS IN THE STEERING PATTERN AS THE PRIMARY STEERING INFLUENCE TRANSITIONS TO A STR CENTERED OVER EASTERN CHINA. 17W IS THEN FORECAST TO TRACK WEST-SOUTHWESTWARD, ALONG THE SOUTHEASTERN EXTENT OF THAT STR THROUGH THE REMAINDER OF THE FORECAST PERIOD. A FINAL LANDFALL IS CURRENTLY FORECAST TO OCCUR JUST BEFORE TAU 120, NORTHWEST OF TAIWAN, THOUGH THERE IS SOME UNCERTAINTY IN THE TIMING AND LOCATION OF THE LANDFALL. IN TERMS OF INTENSITY, 17W IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY OF 110 KTS THROUGH TAU 24 AS THE SYSTEM ATTEMPTS TO RECOVER FROM THE ONGOING ERC. 17W IS ALSO ENTERING WATERS CONTAINING A LOWER OCEAN HEAT CONTENT (OHC), WHICH WILL ALSO HINDER THE CHANCES FOR REDEVELOPMENT AFTER THE ERC COMPLETES. AROUND TAU 24, THE UPPER-LEVEL TROUGH TO THE WEST OF 17W WILL FILL, CAUSING THE POLEWARD OUTFLOW CHANNEL TO WEAKEN. ADDITIONALLY, NORTHERLY SHEAR WILL INCREASE, CAUSING 17W TO GRADUALLY WEAKEN AS IT APPROACHES OKINAWA. ONCE THE SYSTEM ENTERS THE EAST CHINA SEA, NORTHEASTERLY SHEAR INDUCED BY THE STRONG RIDGE OVER CHINA WILL CAUSE FURTHER WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH TAU 72 WITH ONLY NAVGEM BEING AN OUTLIER, WHICH TRACKS THE VORTEX MUCH FURTHER SOUTH. DISCOUNTING NAVGEM, THE CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO ONLY BE ABOUT 90 NM. AFTER TAU 72, THERE IS QUITE A BIT MORE SPREAD BETWEEN MODELS. NOTABLY, THE GFS SHOWS A SHARPER SOUTHWESTWARD TURN, MAKING LANDFALL IN NORTHERN TAIWAN. ON THE OTHER HAND, GALWEM SHOWS NO SOUTHWESTWARD TURN AT ALL AND ACTUALLY SHOWS A TURN TO THE NORTHWEST. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 72 WITH HIGH CONFIDENCE AND THEN CLOSER TO THE EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEAN THROUGH TAU 120 WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE GENERALLY SHOWS A STEADY WEAKENING TREND FROM TAU 24 ONWARD, HOWEVER, THERE ARE SOME MODELS THAT DIFFER. FIRST, COAMPS-TC SHOWS THE SYSTEM MAINTAINING ITS CURRENT INTENSITY THROUGH TAU 60 BEFORE WEAKENING. HAFS-A DEPICTS A PERIOD OF REINTENSIFICATION AFTER PASSING OKINAWA AND IS THE ONLY MODEL TO DO SO. THE PRIMARY REASON FOR THIS IS ATTRIBUTED TO A SIGNIFICANTLY SHARPER SOUTHWESTWARD TURN TOWARD TAIWAN, ALLOWING FOR THE VORTEX TO NOT FEEL THE NORTHEASTERLY SHEAR NEARLY AS MUCH. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGH TAU 72 AND THEN WITHIN THE MAIN GUIDANCE ENVELOPE THROUGH TAU 120 WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN