WDPN31 PGTW 221500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MA-ON) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2N 123.2E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 159 NM NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT THE PREVIOUSLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) HAS NOW TUCKED UNDER AN AREA OF FLARING CONVECTION, WHICH HAS SUCCESSFULLY PUSHED BACK AGAINST THE PERSISTENT, BUT WEAKENING, NORTHEASTERLY FLOW ALOFT. THERE HAS NOT BEEN ANY RECENT MICROWAVE IMAGERY, BUT THE MOST RECENT SSMIS 91GHZ IMAGE FROM 220805Z SHOWED A NAKED CIRCULATION TO THE NORTH OF THE CONVECTION AT THAT TIME, WHICH WAS PRIOR TO THE RECENT FLARE-UP. HOWEVER, AN EXTRAPOLATION OF THE WELL-DEFINED LLCC IN THE MICROWAVE IMAGERY AND AGENCY FIX POSITIONED, LEND MEDIUM CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS INCREASED TO 45 KNOTS, SLIGHTLY ABOVE THE MAJORITY OF AGENCY FIXES BASED ON THE PGTW CURRENT INTENSITY ESTIMATE OF T3.0 AND THE SAME FROM THE RAW ADT. THE SYSTEM HAS SLOWED SIGNIFICANTLY, DOWN TO A FIVE KNOT SOA, AS THE STEERING RIDGE TO THE NORTH HAS WEAKENED A BIT AND WESTERLY FLOW OFFSHORE OF LUZON HAS PUSHED BACK AGAINST THE FORWARD MOTION OF THE SYSTEM. BASED ON JTWC HAND ANALYSIS AND CIMSS ATMOSPHERIC MOTION VECTORS, THE UPPER-LEVEL FLOW PATTERN, WHILE STILL PREDOMINANTLY FROM THE NORTHEAST, HAS BECOME STRONGLY DIVERGENT OVER TOP OF TS 10W, RELAXING THE SHEAR AND ALLOWING FOR DEVELOPMENT OF THE CORE OF THE SYSTEM. THE ENVIRONMENT IS GENERALLY FAVORABLE FOR INTENSIFICATION WITH WARM (30-31C) SSTS, HIGH OHC, LOW (10-15 KNOTS) VWS AND STRONG POLEWARD OUTFLOW. WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS KNES: T2.5 - 35 KTS CIMSS ADT: 39 KTS AT 221210Z CIMSS SATCON: 40 KTS AT 221342Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG EQUATORWARD OTHER FACTORS: HIGH OHC ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. FORECAST DISCUSSION: AS MENTIONED ABOVE, TS 10W HAS SLOWED SIGNIFICANTLY OVER THE PAST SIX HOURS AS THE STEERING RIDGE HAS WEAKENED SLIGHTLY AND IT HAS RUN INTO SOME HEADWINDS FLOWING OFF THE COAST OF LUZON. THE STEERING RIDGE IS FORECAST TO RESTRENGTHEN AND REORIENT TO A SLIGHTLY MORE NORTHWEST TO SOUTHEAST AXIS OVER THE NEXT 12 HOURS. IN COMBINATION WITH THE BUFFER EFFECT OF THE TERRAIN FEATURES OF LUZON, THE SYSTEM IS EXPECTED TO TURN SHARPLY NORTHWARD, MAKE LANDFALL AROUND TAU 12, AND THEN TURN ONTO A MORE NORTHWESTWARD TRACK, REEMERGING OVER WATER OFF THE NORTHWEST COAST OF LUZON BY TAU 24. THE SYSTEM WILL THEN TURN IN A GRACEFUL ARC TOWARDS THE SOUTHEAST COAST OF CHINA, MAKING LANDFALL JUST SOUTH OF HONG KONG JUST PRIOR TO TAU 72 AND THEN MOVING QUICKLY INLAND. WHILE THE SYSTEM IS EXPERIENCING A BETTER ENVIRONMENT CURRENTLY, THE SHORT TIME REMAINING OVER LAND MEANS IT HAS ONLY A SMALL WINDOW OF OPPORTUNITY TO INTENSIFY PRIOR TO LANDFALL, WITH THE CURRENT FORECAST CALLING FOR A PEAK OF 50 KNOTS BY TAU 12. THE SYSTEM WILL WEAKEN SLIGHTLY AS IT CROSSES LUZON DUE TO TERRAIN INFLUENCES, BUT RESTRENGTHEN ONCE IN THE SOUTH CHINA SEA. THE ULTIMATE INTENSITY WILL BE CONSTRAINED BY THE FACT THAT AS THE SYSTEM MOVES ACROSS THE SOUTH CHINA SEA IT WILL BE UNDER THE INFLUENCE OF MODERATE EAST-NORTHEASTERLY FLOW ALOFT, AND WHILE ALL OTHER PARAMETERS ARE FAVORABLE, THE PERSISTENT MODERATE SHEAR WILL LIMIT THE PEAK INTENSITY, CURRENTLY FORECAST AT 55 KNOTS. IT REMAINS POSSIBLE HOWEVER THAT THE SYSTEM COULD BRIEFLY REACH A SLIGHTLY HIGHER INTENSITY BETWEEN TAUS 48 AND 72, NOT CAPTURED IN THE FORECAST, PRIOR TO LANDFALL. ONCE ASHORE IN CHINA, THE SYSTEM WILL RAPIDLY WEAKEN TO BELOW WARNING CRITERIA NO LATER THAN TAU 96. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS IN GOOD AGREEMENT, WITH THE NAVGEM MARKING THE SOUTHERN EDGE OF THE ENVELOPE OVER THE FAR SOUTHERN CHINESE COAST NORTH OF HAINAN, AND THE CTCX AND ECMWF MARKING THE NORTHERN EDGE TAKING THE TRACK OVER HONG KONG. ECENS AND GEFS ENSEMBLE GUIDANCE IS CONSTRAINED IN A SIMILAR ENVELOPE. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND NEAR THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE REMAINS VERY LIMITED DUE TO CONTINUING TECHNICAL ISSUES, AND HAS NOT CHANGED SIGNIFICANTLY FROM THE PREVIOUS FORECAST. THE CTCX AND COTC MODELS REMAIN VERY AGGRESSIVE, PEAKING THE SYSTEM AT OVER 75 KNOTS PRIOR TO LANDFALL, BUT THE JTWC FORECAST REMAINS WELL BELOW THESE OVERLY AGGRESSIVE ESTIMATES. HOWEVER, DUE TO THE LACK OF RELIABLE INTENSITY GUIDANCE, CONFIDENCE REMAINS LOW. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN