WDPN33 PGTW 161500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.8N 118.9E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 334 NM NORTH-NORTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 30 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: HAVING UNDERGONE A PERIOD OF ARRESTED DEVELOPMENT OVER THE PREVIOUS SIX HOURS, TY 23W HAS STARTED ANOTHER ROUND OF RENEWED INTENSIFICATION. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A REDEVELOPED 40NM WIDE EYE FEATURE, WITH RELATIVELY WEAK CONVECTION IN THE NORTHEAST QUADRANT, AND DEEP CONVECTION DEVELOPING IN THE SOUTHWEST QUADRANT AND MOVING UPSHEAR. A 161021Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED DEEP CONVECTIVE BANDS WRAPPING INTO A WELL DEFINED MICROWAVE EYE, AND A SLIGHT WESTWARD TILT WITH HEIGHT COMPARED TO THE LOWER LEVEL EYE EVIDENT IN THE 37GHZ IMAGE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON MULTIPLE AGENCY FIX POSITIONS AND AN EXTRAPOLATION OF THE 37GHZ MICROWAVE EYE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, GENERALLY IN LINE WITH THE PGTW AND KNES T4.5 DVORAK CURRENT INTENSITY ESTIMATES, BUT BELOW THE ELEVATED ADT VALUES. ADDITIONAL SUPPORT FOR THE 75 KNOT INITIAL INTENSITY COMES FROM THE AIDT AND OPEN-AIIR TECHNIQUES, BOTH OF WHICH ARE ESTIMATING 74 KNOTS. EASTERLY SHEAR IS NOW ABOUT 10 KNOTS LOWER THAN SIX HOURS AGO BASED ON CIMSS VWS ESTIMATES, PROVIDING SUPPORT FOR THE RESURGENCE OF THE EYE AND RENEWED INTENSIFICATION, WITH THE OTHER ENVIRONMENTAL PARAMETERS REMAINING FAVORABLE. THERE DOES HOWEVER APPEAR TO BE SOME INFLUX OF DRY AIR SURGING UP FROM THE SOUTH AND WRAPPING INTO THE EASTERN SIDE OF THE EYEWALL, WHERE CONVECTION IS STRUGGLING TO MAINTAIN ITSELF, PRECLUDING DEVELOPMENT OF A COMPLETE EYEWALL. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN SIDE OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS RJTD: T3.5 - 55 KTS KNES: T4.5 - 77 KTS CIMSS ADT: 82 KTS AT 161210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: DRY AIR ENTRAINMENT IN THE EASTERN HEMISPHERE OF THE CIRCULATION. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 23W HAS LIKELY REACHED ITS MAXIMUM NORTHWARD POINT, RIGHT AROUND THE 20TH PARALLEL, WITH ANIMATED EIR OVER THE PAST TWO HOURS SUGGESTING A DUE WEST TRACK. THE SYSTEM HAS REACHED THE INFLECTION POINT DUE SOUTH OF A BREAK IN THE RIDGE INDUCED BY A PASSING MID-LATITUDE TROUGH OVER NORTHEAST CHINA. WHILE THE TROUGH IS NOT DEEP ENOUGH TO DIRECTLY IMPACT THE TRACK OF TY 23W, THE WEAKENING OF THE STEERING GRADIENT MEANS THAT THE SYSTEM SHOULD SLOW DOWN A BIT AS IT TRACKS MORE WESTWARD THROUGH THE NEXT 12 HOURS OR SO. BY AROUND TAU 24 THE STEERING MECHANISM SHIFTS TO A BUILDING STR OVER SOUTHEAST CHINA, WHICH WILL PUSH TY 23W ONTO A SOUTHWESTWARD TRACK THROUGH ABOUT TAU 48. BY TAU 48 THE STR WILL QUICKLY REPOSITION TO NEAR TAIWAN WITH THE WESTERN SIDE OF THE RIDGE BECOMING ORIENTED TO A MORE NORTHWEST TO SOUTHEAST AXIS. THIS WILL LEAD TO A GRACEFULLY ARCING TRACK, GRADUALLY TURNING TOWARDS THE NORTHWEST AFTER TAU 72. THE SYSTEM IS CURRENTLY FORECAST TO SKIRT THE SOUTHERN COAST OF HAINAN ISLAND AROUND TAU 72 AND THEN MOVE INTO THE SOUTHERN GULF OF TONKIN, WITH LANDFALL SOUTH OF HANOI EXPECTED NEAR TAU 120. THE PRIMARY INFLUENCE ON INTENSIFICATION IN THE NEXT 24 HOURS WILL BE THE DRY AIR WHICH IS CLEARLY IMPINGING ON THE EASTERN SIDE OF THE SYSTEM. THERE ARE SIGNS THAT THIS DRY AIR WILL RECEDE AND MOISTEN OVER THE NEXT 24 HOURS, AND THUS THE SYSTEM IS FORECAST TO INTENSIFY TO A PEAK OF 95 KNOTS BY TAU 24. THEREAFTER, THE SHEAR VECTOR IS EXPECTED TO SHIFT TO A SOUTHERLY DIRECTION, WITH SHEAR VALUES ANTICIPATED TO INCREASE SHARPLY, RESULTING IN A SLOW BUT STEADY WEAKENING TREND THROUGH TAU 72. AS THE SYSTEM APPROACHES HAINAN, DISRUPTION OF THE LOW-LEVEL INFLOW AND VORTEX, ALONG WITH ENCROACHMENT OF DRY AIR FROM THE WEST AND SOUTH, WILL COMBINE TO QUICKEN THE PACE OF WEAKENING, SUCH THAT BY THE TIME THE SYSTEM MAKES LANDFALL IN NORTHERN VIETNAM, IT WILL BE A MINIMAL TROPICAL DEPRESSION. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS IN GOOD AGREEMENT ON THE GENERAL TRACK SCENARIO THROUGH MOST OF THE FORECAST BUT IS STARTED TO INDICATE INCREASED UNCERTAINTY TOWARDS THE END OF THE FORECAST PERIOD. THE GUIDANCE ENVELOPE IS DEFINED BY NAVGEM ON THE NORTHERN EDGE AND THE UKMET ENSEMBLE MEAN ON THE SOUTH, WITH SPREAD GRADUALLY INCREASING TO 135NM AT TAU 72. AT THIS POINT THINGS BEGIN TO DIVERGE DRASTICALLY, WITH THE ECMWF AND UKMET ENSEMBLES AS WELL AS THE GALWEM TURNING THE SYSTEM SHARPLY SOUTHWARDS, OR EVEN DOUBLING BACK TOWARDS THE EAST, AROUND TAU 96. MEANWHILE THE HWRF AND COAMPS-TC TRACKERS RACE THE SYSTEM STRAIGHT AHEAD, FAR OUTPACING THE REMAINDER OF THE GUIDANCE WHICH REMAINS CLUSTERED ON A SLIGHTLY SLOWER TRACK WHICH REMAINS OVER WATER BY TAU 120. THE JTWC FORECAST IS LAID ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE THROUGH TAU 72 WITH HIGH CONFIDENCE, THEN MOST CLOSELY TRACKS THE GFS SOLUTION THROUGH TAU 96 WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE REMAINS MIXED, WITH RIPA, RI25 AND RI30 CONTINUING TO FIRE, PEAKING AS HIGH AS 110 KNOTS, WHILE THE DECAY SHIPS AND GFS DETERMINISTIC MODELS DEPICT A PEAK CLOSER TO 80 KNOTS. THE JTWC FORECAST LIES SLIGHTLY ABOVE THE COAMPS-TC (GFS VERSION) AND CONSENSUS MEAN PEAK OF 92 KNOTS THROUGH TAU 24, THEN LIES SLIGHTLY ABOVE THE CONSENSUS MEAN THROUGH THE REMAINDER OF THE FORECAST WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN