WDPN31 PGTW 232100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 022// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 23.2N 137.9E INITIAL INTENSITY: 110 KTS GEOGRAPHIC REFERENCE: 584 NM EAST-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS SIGNIFICANT WAVE HEIGHT: 48 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN APPROXIMATELY 15NM WIDE EYE FEATURE, WHICH IN THE MOST RECENT FRAMES OF EIR APPEARS TO BE SHRINKING ONCE AGAIN. THE EYEWALL REPLACEMENT CYCLE (ERC) WHICH STARTED YESTERDAY IS LIKELY ONGOING, ALTHOUGH A LACK OF RECENT MICROWAVE IMAGERY MAKES DETERMINATION OF THE CURRENT STATUS CHALLENGING. HOWEVER, THE OVERALL STRUCTURAL APPEARANCE OF THE SYSTEM IN THE EIR ALONG WITH A COMPARISON TO A 10 HOUR OLD MICROWAVE IMAGE SUGGESTS THAT THE ERC HAS NOT YET FULLY COMPLETED. ANIMATED WATER VAPOR IMAGERY DEPICTS AN UPPER-LEVEL ANTICYCLONE DRAPED ACROSS THE NORTH- NORTHEASTERN SIDE OF THE SYSTEM, INDUCING LIGHT EASTERLY FLOW ALOFT AND EASTERLY SHEAR OVER TOP OF TY 17W. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE IN THE EIR. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE FAVORABLE OVERALL, WITH LIGHT WIND SHEAR, WARM SSTS, HIGH OHC AND MODERATE OUTFLOW ALOFT, OFFSET BY THE IMPACTS OF THE ONGOING ERC. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) WHICH EXTENDS SOUTHEASTWARD FROM SOUTHERN JAPAN TO A POSITION NORTHEAST OF GUAM. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T5.5 - 102 KTS RCTP: T5.5 - 102 KTS KNES: T5.5 - 102 KTS CIMSS SATCON: 116 KTS AT 231830Z CIMSS ADT: 112 KTS AT 231830Z CIMSS AIDT: 105 KTS AT 231830Z CIMSS D-MINT: 105 KTS AT 231646Z CIMSS D-PRINT: 108 KTS AT 231800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL OTHER FACTORS: ONGOING EYEWALL REPLACEMENT CYCLE (ERC) 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: TYPHOON (TY) 17W (SAUDEL) CONTINUES TO TRACK WEST- NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF THE EXPANSIVE STR SITUATED TO THE NORTHEAST. NO SIGNIFICANT CHANGES IN TRACK OR SPEED IS EXPECTED FOR THE 36 HOURS AS THE STR IS FORECAST TO REMAIN FIRMLY ENTRENCHED. AROUND TAU 36 HOWEVER, THE RIDGING PATTERN BEGINS TO SHIFT, WITH A WEAKNESS OR BREAK IN THE RIDGE DEVELOPING OVER SOUTH KOREA. AS TY 17W APPROACHES THE RYUKYU ISLANDS, IT WILL BEGIN TO SLOW DOWN WHILE CONTINUING TO GAIN LATITUDE. AROUND TAU 60, THE SYSTEM REACHES AN INFLECTION POINT, REACHING ITS FURTHEST POLEWARD EXTENT, AND BEGINS TO GRADUALLY TURN WESTWARD AS THE PRIMARY STEERING INFLUENCE SHIFTS TO A BUILDING RIDGE OVER EASTERN CHINA. AFTER TAU 72, THE STEERING SHIFT WILL BE COMPLETE, AND TY 17W WILL QUICKLY TURN SOUTHWESTWARD ALONG THE SOUTHEASTERN FLANK OF THE BUILDING RIDGE TO THE WEST. THE SYSTEM IS EXPECTED TO MAKE LANDFALL ALONG THE SOUTHEASTERN COAST OF CHINA BY TAU 120. REGARDING INTENSITY, THE LENGTHY ERC HAS PROVEN TO BE A SIGNIFICANT INHIBITING FACTOR, PRECLUDING TY 17W FROM REACHING ITS INITIALLY PREDICTED INTENSITY. AT THIS POINT, ONCE THE ERC WRAPS UP, THE SYSTEM WILL HAVE MOVED INTO A LESS FAVORABLE ENVIRONMENT WHICH WILL LIMIT ITS ABILITY TO REINTENSIFY POST-ERC. THE PRIMARY INHIBITOR GOING FORWARD WILL BE A LACK OF OUTFLOW, WHICH WILL BE CHOKED OFF BY THE PRESENCE OF A NEARBY UPPER-LEVEL ANTICYCLONE TO THE NORTH. AS THE SYSTEM BECOMES ISOLATED FROM AN OUTFLOW PERSPECTIVE, IT ALSO BECOMES COMPLETELY SURROUNDED BY DRY AIR, IN EFFECT COCOONING THE SYSTEM. INTENSITY IS FORECAST TO REMAIN RELATIVELY STEADY FOR THE FIRST 36 HOURS, THEN BEGIN TO STEADILY WEAKEN THROUGH THE REMAINDER OF THE FORECAST. MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EARLY PHASES OF THE FORECAST. CROSS-TRACK SPREAD INCREASES TO 165NM BY TAU 72, WITH NAVGEM DIVERGING FROM THE REMAINDER OF THE GUIDANCE AND MARKING THE SOUTHERN OUTLIER, WHILE THE GFS AND AI-BASED MODELS MARK THE NORTHERN EDGE OF THE ENVELOPE. THROUGH TAU 72, ENSEMBLE MEMBER DISPERSION IS MINOR, AND THE ENSEMBLE MEAN TRACKERS ARE CONSISTENT WITH THE CONSENSUS MEAN. THE JTWC FORECAST THROUGH TAU 72 IS PLACED NEAR THE AI CONSENSUS WITH HIGH CONFIDENCE. AFTER TAU 72, CROSS-TRACK MODEL SPREAD INCREASES TO NEARLY 400NM, WITH THE GALWEM TRACK THIS SYSTEM WESTWARD INTO CHINA ALONG THE 28TH PARALLEL, WHILE GFS DIVES THE SYSTEM JUST WEST OF ISHIKAGIJIMA BEFORE MAKING LANDFALL ALONG THE EAST-CENTRAL COAST OF TAIWAN PRIOR TO TAU 120. THE REMAINDER OF THE GUIDANCE MEMBERS ARE DISPERSED BETWEEN THE TWO OUTLIERS. ENSEMBLE DISPERSION INCREASES SHARPLY AFTER TAU 72 AS WELL, WITH THE EXPERIMENTAL JTWC SUPER ENSEMBLE DEPICTING MEMBERS EXTENDING FROM THE SOUTH COAST OF KOREA ALL THE WAY TO HAINAN, THOUGH THE MOST CONCENTRATED TRACK DENSITY IS FOCUSED ALONG THE OVERALL ENSEMBLE MEAN TRACK. THE JTWC FORECAST IS PLACED NEAR THE EXPERIMENTAL GOOGLE DEEPMIND TRACKER THROUGH TAU 120, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN STRONG AGREEMENT DEPICTING A FLAT INTENSITY TREND THROUGH TAU 36 FOLLOWED BY STEADY WEAKENING THROUGH TAU 120. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN