WDPN31 PGTW 151500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W (SINLAKU) WARNING NR 027// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2N 144.6E INITIAL INTENSITY: 110 KTS GEOGRAPHIC REFERENCE: 92 NM NORTHWEST OF SAIPAN MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 39 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE, POWERFUL TYPHOON WITH AN EYE MEASURING 30 NM IN DIAMETER. THE STORM MOTION HAS SLOWED FROM 06 KTS TO 04 KTS TOWARDS THE NORTHWEST OVER THE PAST 06 HOURS, PROLONGING THE DESTRUCTIVE IMPACTS FOR THE MARIANA ISLANDS. THE CONVECTIVE STRUCTURE HAS IMPROVED SLIGHTLY, WITH COOLING SURROUNDING CLOUD TOPS AND EXPANDING RADIAL OUTFLOW. A 150801Z WSF-M MWI 37 GHZ IMAGE DEPICTED AN OUTER, 100 NM-WIDE, CONVECTIVE RING IN WHAT MAY FORESHADOW A SECOND EYEWALL REPLACEMENT CYCLE (ERC). IN FACT, EIR IMAGERY IS BEGINNING TO SHOW A MOAT FORMING IN THE NORTHERN SEMICIRCLE, SEPARATING THE EXTREMELY LARGE RING WITH THE INNER EYEWALL. DEEP CONVECTION HAS FLARED OVER LARGE SECTIONS OF THE OUTER BAND. A TIMELY 151156Z ASCAT-C PASS CONFIRMS THAT THE WIND FIELD IS VERY LARGE, WITH GALES EXTENDING OUTWARD TO OVER 200 NM. GUAM WILL BE SITUATED WITHIN THE 34-KT WIND RADII FOR AT LEAST THE NEXT 12 HOURS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE DEFINED EYE ON EIR IMAGERY. THE INITIAL INTENSITY IS HELD AT 110 KTS BASED A BLEND OF AGENCY DVORAK FIXES RANGING FROM T5.5 TO T6.5. THE DVORAK ESTIMATE FROM KNES INCREASED TO T6.0, AND THE CIMSS AI-RI INDICATES A 25 PERCENT PROBABILITY OF A 30 KT INCREASE IN 24 HOURS, THOUGH THIS APPEARS UNLIKELY GIVEN THE SIZE OF THE STORM. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: NORTHERN EXTENSION OF A NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.5 - 102 KTS RJTD: T6.5 - 127 KTS RCTP: T6.5 - 127 KTS KNES: T6.0 - 115 KTS CIMSS ADT: 94 KTS AT 151140Z CIMSS AIDT: 100 KTS AT 151140Z CIMSS D-PRINT: 104 KTS AT 151200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST FOR THE FIRST 36 HOURS HAS BEEN INCREASED. FORECAST DISCUSSION: TY 04W IS BEING STEERED VERY SLOWLY TO THE NORTHWEST BY THE NORTHERN EXTENSION OF A NER TO THE SOUTHEAST. THIS RIDGE HAS EXTENDED TO THE NORTHEAST OF THE SYSTEM, THEREBY SUPPRESSING THE NORTHWARD MOTION FOR THE MOMENT. THE OVERALL TRACK HAS SHIFTED 10-20 NM POLEWARD DUE TO THE INITIAL SLOWER SPEED. THE EXTRA TIME WILL ALLOW THE RIDGE TO THE EAST TO BUILD MORE STRONGLY AND STEER THE SYSTEM FURTHER TO THE NORTH. A TROUGH PASSING OVER HONSHU WILL IMMINENTLY ERODE THE FAR NORTHERN EXTENSION OF THE RIDGE AND ALLOW FOR A SLIGHTLY FASTER TRAJECTORY TOWARDS THE NORTH. AS THE STORM GAINS LATITUDE, IT WILL COME UNDER THE INFLUENCE OF THE MID-LATITUDE WESTERLIES, WHICH WILL IMPART AN EASTWARD FORCE ON DIRECTION OF TRAVEL. TY SINLAKU WILL TURN TOWARDS THE NORTH-NORTHEAST AT TAU 24 AND THEN NORTHEAST TO EAST-NORTHEAST AT TAU 72, BECOMING EMBEDDED IN THE WESTERLY FLOW. THE ENVIRONMENT WILL REMAIN FAVORABLE FOR DEVELOPMENT, CHARACTERIZED BY MINIMAL VWS AND 28 DEGREE CELSIUS SST. WITH THE SATELLITE PRESENTATION OF TY 04W IMPROVING, THE FORECAST NOW CALLS FOR SLIGHT INTENSIFICATION TO AT LEAST 115 KTS DURING THE NEXT 24 HOURS, LIMITED BY POTENTIAL ERC. STEADY TO RAPID WEAKENING WILL COMMENCE AFTER TAU 24 AS THE STORM TRAVELS OVER SEA SURFACE TEMPERATURES (SST) OF BELOW 26 DEGREES CELSIUS AND THE VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH THE WESTERLIES INCREASES TO 20-30 KTS. THE VWS WILL RAPIDLY ERODE THE WESTERN SIDE OF THE CIRCULATION AND ENABLE DRY AIR TO RAPIDLY INFILTRATE THE INNER CORE. EXTRATROPICAL TRANSITION WILL BEGIN AT TAU 96 AND QUICKLY COMPLETE BY TAU 120. MODEL DISCUSSION: NAVGEM HAS ONCE AGAIN BECOME THE OUTLIER, DEPICTING A MORE POLEWARD TRAJECTORY FOR THE FIRST 72 HOURS. NOTABLY, ECMWF HAS ALSO SHIFTED POLEWARD. FOR NOW, THE JTWC TRACK IS LAID ON TOP OF THE TIGHT GROUPING OF MODELS CONSISTING OF HAFS-A, GFS, AND COAMPS-TC, ALL OF WHICH ARE AT THE CENTER OF THE GUIDANCE ENVELOPE. HOWEVER, FUTURE ADJUSTMENTS TO THE NORTH MAY BE NECESSARY. EXCLUDING NAVGEM, THE CROSS-TRACK SPREAD IS 40 NM AT TAU 24 AND 50 NM AT TAU 48. THE ALONG-TRACK SPREAD IS LOW THROUGH TAU 96. THESE FACTORS GIVE HIGH CONFIDENCE TO THE 72-HR FORECAST TRACK AND MEDIUM CONFIDENCE THEREAFTER. THE JTWC INTENSITY FORECAST IS SET ABOVE ALL OF THE RELIABLE INTENSITY AIDS AND IS CLOSEST TO ECMWF FOR THE FIRST 24 HOURS TO ACCOUNT FOR THE TRENDS OBSERVED IN THE EIR IMAGERY. THE INTENSITY FORECAST THEN ALIGNS MORE CLOSELY WITH HAFS-A AND HWRF FROM TAU 48 TO TAU 72. THE EXTRATROPICAL TRANSITION TO A 55 KT, STORM-FORCE LOW ALIGNS BEST WITH THE GFS MODEL AT THE END OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN