WDPN33 PGTW 151500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.8N 123.0E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 277 NM NORTH-NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SOMEWHAT LOPSIDED SYSTEM, WITH PERSISTENT BUT DISORGANIZED DEEP CONVECTION PUSHED TO THE WEST OF THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC) BY PERSISTENT MODERATE EASTERLY SHEAR. THE LLCC REMAINS OBSCURED BY CIRRUS BLOWOFF THOUGH THE EXTREME OUTER BANDS ARE EVIDENT IN THE CLEAR AIR EAST OF THE CENTER. A 151025Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED A PARTIALLY EXPOSED LLCC TO THE EAST OF A MID-LEVEL MICROWAVE EYE FEATURE, REPRESENTING THE WESTERLY TILT OF THE VORTEX WITH HEIGHT TO GOOD EFFECT. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC SEEN IN THE MICROWAVE IMAGERY AND JUST SOUTH OF THE PGTW AND RJTD FIX POSITIONS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE T2.5 DVORAK CURRENT INTENSITY ESTIMATES FROM PGTW AND KNES, SUPPORTED BY THE ADT AND AIDT AS WELL AS THE EXPERIMENTAL CIMSS DEEP MICRONET (DMN) AND OPEN-AIIR, BOTH ESTIMATING AN INTENSITY OF 40 KNOTS AT 1200Z. WITH THE EXCEPTION OF THE MODERATE EASTERLY SHEAR (CIMSS ANALYSIS IS 15.5 KNOTS), THE OVERALL ENVIRONMENT IS FAVORABLE WITH GOOD WESTWARD OUTFLOW AND WARM SSTS. THE SYSTEM IS TRACKING TOWARDS THE WEST ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED SOUTHEAST OF KYUSHU AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T2.5 - 35 KTS CIMSS ADT: 41 KTS AT 151210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE STEERING RIDGE TO THE NORTH HAS STARTED TO MOVE EASTWARD, WITH THE SOUTHWESTERN SIDE OF RIDGE ORIENTING TO A MORE NORTHWEST-SOUTHEAST AXIS, ALLOWING FOR TS 23W TO TRACK SLIGHTLY NORTH OF DUE WEST OVER THE PAST SIX HOURS. THIS TREND IS EXPECTED TO CONTINUE AS A MID-LATITUDE TROUGH MOVING IN FROM THE WEST WILL ERODE THE STR AND INDUCE A WEAKNESS WHICH WILL PULL TS 23W SLIGHTLY MORE POLEWARD THROUGH TAU 36, THOUGH THE TROUGH IS FAR ENOUGH NORTH THAT THE EFFECT WILL BE RELATIVELY SMALL. BY TAU 36, THE SYSTEM REACHES AND INFLECTION POINT AND SLOWS DOWN AS IT WEAKNESS IN THE RIDGE LIES DUE NORTH OF THE SYSTEM. AFTER THIS POINT A STR CENTERED OVER NORTHERN MYANMAR WILL BUILD TOWARDS THE EAST AND ASSUME THE DOMINANT STEERING ROLE. AT THE SAME TIME, STRONG NORTHEASTERLY FLOW WILL DIVE DOWN OUT OF THE TAIWAN STRAIT, SLIDING SOUTHWARDS ALONG THE WESTERN SIDE OF TS 23W. THE COMBINED EFFECTS OF THESE PATTERN CHANGES WILL TURN TS 23W ONTO A SOUTHWESTWARD TRACK AFTER TAU 36. BY TAU 96 THE PATTERN SHIFTS AGAIN, WITH THE STR SHIFTING TO A POSITION OVER THE TAIWAN STRAIT, ALLOWING FOR TS 23W TO TURN NORTHWESTWARD ONCE MORE TOWARDS THE END OF THE FORECAST, SKIRTING THE COAST OF HAINAN. IN THE NEAR-TERM, THE SYSTEM IS STILL STRUGGLING TO CONSOLIDATE A VERTICALLY STACKED CONVECTIVE CORE. RECENT WATER VAPOR IMAGERY SUGGESTS THE DEVELOPMENT OF AN UPSHEAR ARC, SUGGESTIVE OF A POSSIBLE MESOSCALE REDUCTION IN SHEAR, WHICH WOULD ALLOW FOR A MORE RAPID PACE OF INTENSIFICATION. HOWEVER, THE PROXIMITY OF THE LLCC TO LUZON WILL DISRUPT THE LOW-LEVEL FLOW PATTERN SUFFICIENTLY TO OFFSET THE REDUCED SHEAR AND ONLY MODEST INTENSIFICATION IS EXPECTED FOR THE NEXT 12 HOURS. ONCE THE SYSTEM EMERGES BACK OVER OPEN WATERS, THE FORECAST CALLS FOR A FASTER RATE OF INTENSIFICATION, AS THE SYSTEM MOVES AWAY FROM THE TERRAIN AND TAPS INTO A STRONGER OUTFLOW REGIME. PEAK INTENSITY IS FORECAST AROUND TAU 48, BUT AFTER THIS POINT THE SYSTEM WEAKENS THROUGH THE REMAINDER OF THE FORECAST DUE TO THE EFFECTS OF INCREASING SHEAR, AND ENTRAINMENT OF DRY AIR FROM THE WEST, ESPECIALLY AFTER TAU 96. MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72, WITH ALL CONSENSUS MEMBERS ALIGNED WITHIN A TIGHT ENVELOPE THAT GRADUALLY EXPANDS TO 80NM AT TAU 72. THEREAFTER THE MODELS DO BEGIN TO DIVERGE WITH SPREAD INCREASING TO 230NM BY TAU 120. ENSEMBLE GUIDANCE SUPPORTS THE OVERALL TRACK SCENARIO BUT DOES SHOW A WIDER RANGE OF POTENTIAL TRACKS, WITH BOTH THE GEFS AND ECENS MEANS INDICATING A TRACK INTO NORTH CENTRAL VIETNAM, WHILE THE DETERMINISTIC TRACKERS TAKE THE SYSTEM INTO THE GULF OF TONKIN. THE JTWC TRACK IS IN THE MIDDLE OF THE PACK THROUGH TAU 72, THEN MOVES TO THE NORTHERN SIDE OF THE ENVELOPE THROUGH TAU 120, WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE REMAINS MIXED, WITH CTCX, CTR1 AND HWRF MARKING THE HIGH END, PEAKING BETWEEN 95-115 KNOTS, WHILE THE COTC AND DECAY SHIPS (NAVGEM AND GFS) MARKING THE LOW END, PEAKING THE SYSTEM AT JUST 60 KNOTS. ENSEMBLE INTENSITY GUIDANCE HAS BACKED OFF THE RAPID INTENSIFICATION PROBABILITIES, BUT CONTINUES TO SHOW VERY HIGH PROBABILITIES OF MODERATE INTENSIFICATION. THE JTWC FORECAST LIES CLOSE TO THE HWRF SOLUTION AND ABOUT 10 KNOTS LOWER THAN THE CTCX PEAK AND WELL ABOVE THE CONSENSUS MEAN, WHICH IS BEING PULLED LOWER DUE TO THE DECAY SHIPS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN