WDPN31 PGTW 141500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W (SINLAKU) WARNING NR 023// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.9N 145.8E INITIAL INTENSITY: 125 KTS GEOGRAPHIC REFERENCE: 18 NM SOUTH OF SAIPAN MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 45 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SLOWLY WEAKENING TYPHOON UNDERGOING AN EYEWALL REPLACEMENT CYCLE (ERC). WHILE THE CENTRAL DENSE OVERCAST (CDO) HAS BECOME MORE RAGGED, THE CONVECTION REMAINS HEALTHY, WITH CLOUD TOP TEMPERATURES AS COLD AS -80 DEGREES CELSIUS. THE CONVECTION IS NOW PRIMARILY WRAPPING AROUND THE OUTER EYEWALL WITH THE INNER EYEWALL ERODING AWAY, WHICH IS CLEARLY SHOWCASED BY A 140821Z WSF-M MWI 89 GHZ IMAGE. THE PGUA RADAR CONFIRMS THAT THE INNER EYEWALL IS SHALLOWING OUT AND OPENING UP, ENABLING A GRADUAL OUTWARD TRANSFER OF MOMENTUM TO THE CONSOLIDATING OUTER EYEWALL. FOR 141200Z, THE RADIUS OF MAXIMUM WIND WILL REMAIN ALIGNED WITH THE INNER EYEWALL, GIVEN THAT SAIPAN INTERNATIONAL AIRPORT IS REPORTING EVEN HIGHER WIND SPEEDS INSIDE THE OUTER RING. IN FACT, THE AIRPORT SENSOR REPORTED A SUSTAINED WIND OF 71 KTS AND A GUST OF 113 KTS AT 141200Z, AND EARLIER METAR RETURNED A MEAN SEA LEVEL PRESSURE OF 948.8 MB. ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH AMPLE OCEAN HEAT CONTENT OF NEAR 150 KJ CM2, ABUNDANT DEEP-LAYER MOISTURE, AND LOW VERTICAL WIND SHEAR (VWS), THOUGH THE ONGOING ERC IS LEADING TO SOME WEAKENING. THE UPPER-LEVEL OUTFLOW REMAINS ROBUST IN THE WESTERN SEMICIRCLE BUT IS SOMEWHAT RESTRICTED IN THE SOUTHEAST QUADRANT. THE FORWARD SPEED OF TYPHOON 04W HAS SIGNIFICANTLY SLOWED TO 04 KTS, PROLONGING THE DESTRUCTIVE CONDITIONS OVER THE MARIANA ISLANDS. AFTER A BRIEF WEST-NORTHWEST MOTION, SINLAKU APPEARS TO HAVE RESUMED ITS AVERAGE TRAJECTORY TOWARDS THE NORTHWEST, AND THE WESTERN EYEWALL HAS MOVED OVER SAIPAN AND TINIAN. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN THE EIR AND RADAR IMAGERY. THE INITIAL INTENSITY IS SET AT 125 KTS WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE T6.0-T7.0 DVORAK FIXES FROM PGTW, KNES, RJTD, AND RCTP. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.5 - 127 KTS RJTD: T7.0 - 140 KTS RCTP: T7.0 - 140 KTS KNES: T6.0 - 115 KTS CIMSS ADT: 119 KTS AT 141140Z CIMSS AIDT: 114 KTS AT 141140Z CIMSS D-PRINT: 121 KTS AT 141140Z 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: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 04W WILL CONTINUE TO SLOWLY TRAVEL TOO THE NORTHWEST UNDER THE STEERING INFLUENCE OF THE BUILDING NEAR TO THE EAST. AS SINLAKU GAINS LATITUDE AND APPROACHES A WEAKNESS IN THE SUBTROPICAL RIDGE (STR) TO THE NORTH, IT WILL BEGIN ROUND THE STR AXIS BY TAU 24. A SHARPENING SHORTWAVE TROUGH PASSING SOUTH OF HONSHU WILL BRIEFLY ERODE THE STR, ALLOWING FOR A MORE NORTHWARD TO NORTH- NORTHEASTWARD MOTION AND A GRADUAL INCREASE IN FORWARD SPEED. BY TAU 72, THE SYSTEM WILL BECOME INCREASINGLY EMBEDDED IN THE WESTERLIES POLEWARD OF THE STR AXIS, ACCELERATE TOWARDS THE NORTHEAST, AND UNDERGO EXTRATROPICAL TRANSITION (ETT) AS A STORM-FORCE LOW. THE POWERFUL TYPHOON CONTINUES TO SLOWLY WEAKEN DUE TO THE ERC. FOR THE NEXT 24 HOURS, ENVIRONMENTAL CONDITIONS WILL BE CONDUCIVE DUE TO LOW VWS, WARM SEA SURFACE TEMPERATURES (SST), AND AMPLE MID-LEVEL MOISTURE. IF THE SYSTEM IS ABLE TO QUICKLY COMPLETE THE ERC, THE INTENSITY WILL HOLD, AND SLIGHT INTENSIFICATION IS NOT OUT OF THE QUESTION. THE FORECAST INTENSITY REFLECTS A SCENARIO IN WHICH THE ERC WILL BE SLOW TO COMPLETE, AND THE INITIAL RATE OF WEAKENING WILL BE SLOW. ENVIRONMENTAL ANALYSIS DEPICTS A VAST REGION OF DRY AIR IMMEDIATELY WEST OF THE STORM. FASTER WEAKENING WILL COMMENCE BEYOND TAU 24 AS TY 04W TRAVERSES OVER PROGRESSIVELY COOLER SST AND ENTERS A DRIER, MORE STABLE ENVIRONMENT WITH A SIGNIFICANTLY LARGER EYE. MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, MODELS ARE IN FAIR AGREEMENT FOR THE FIRST 48 HOURS. THE CROSS-TRACK SPREAD INCREASES FROM 55 NM AT TAU 24 TO 100 NM AT TAU 48, THOUGH A LARGE MAJORITY OF MODELS ARE GROUPED TIGHTLY WITHIN THE CENTER OF THE UNCERTAINTY ENVELOPE. GREATER SPREAD ARISES AT THE LATER TAUS BECAUSE DIFFERENCES IN HOW THE MODELS HANDLE THE EVOLUTION OF THE TROUGHS PASSING NORTH OF THE STR AND THE STRENGTH OF THE STR SHAPE THE AMOUNT OF RECURVATURE IN THE TRACK. THE JTWC FORECAST TRACK IS LAID WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER, ALIGNING CLOSELY WITH THE GROUPING CONSISTING OF HAFS-A, THE GFS ENSEMBLE MEAN, ECMWF, AND GALWEM. THE INTENSITY FORECAST IS SET CLOSE TO HAFS-A AND THE MULTI-MODEL CONSENSUS IN DEPICTING SLOW INITIAL WEAKENING FOLLOWED BY STEADY WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. COAMPS-TC AND GFS DEPICT RAPID WEAKENING, THE SOLUTIONS OF WHICH ARE DISCOUNTED AS BEING UNREALISTIC GIVEN THE FAVORABLE CONDITIONS. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN