WDPN31 PGTW 260300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.5N 117.6E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 235 NM WEST-SOUTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 17 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAGGED AND RELATIVELY DISORGANIZED CENTRAL DENSE OVERCAST (CDO) FEATURE, WITH ISOLATED VORTICAL HOT TOWERS AND OVERSHOOTING TOPS, WHICH ARE STARTING TO SHOW SIGNS OF ORGANIZING AROUND THE LIKELY VORTEX. A 252254Z SSMIS 91GHZ MICROWAVE IMAGE SUGGESTS A NASCENT MICROWAVE EYE FEATURE, WITH DEEP CONVECTION TO THE WEST AND SOUTHEAST OF THE CENTER, STARTING TO WRAP IN TOWARDS THE CENTER. HOWEVER, THERE APPEARS TO BE A FAIR AMOUNT OF VORTEX TILT TOWARDS THE NORTH WITH HEIGHT, BASED ON A COMPARISON OF THE 91GHZ AND 37GHZ CHANNELS AND CONFIRMED BY HAFS-A MODEL CROSS-SECTIONS. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE DUE TO THE WIDE DISPERSAL BETWEEN THE KNES, RJTD AND PGTW FIX POSITIONS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, BASED ON THE T3.5 DVORAK CURRENT INTENSITY ESTIMATES FROM BOTH PGTW AND KNES ALONG WITH THE CIMSS ADT AND AIDT ESTIMATES IN THE 50-59 KNOT RANGE. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, WITH DEEP-LAYER SHEAR STEADILY DECREASING, OUTFLOW ALOFT IMPROVING AND SSTS REMAINING QUITE WARM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED OVER THE PHILIPPINE SEA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.0 - 45 KTS RCTP: T3.0 - 45 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 48 KTS AT 252030Z CIMSS ADT: 59 KTS AT 260030Z CIMSS AIDT: 48 KTS AT 260000Z CIMSS D-MINT: 46 KTS AT 252253Z CIMSS D-PRINT: 47 KTS AT 260020Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: TROPICAL STORM (TS) 33W HAS SPED UP CONSIDERABLY OVER THE PAST SIX HOURS, NOW TRUCKING WEST-NORTHWESTWARD AT 17 KNOTS, AS THE STEERING GRADIENT IS NOW REACHING ITS STRONGEST. FROM THIS POINT FORWARD HOWEVER, THE SYSTEM IS EXPECTED TO BEGIN A STEADY SLOW-DOWN AS THE TRAJECTORY FLATTENS OUT A BIT, TO A MORE WESTWARD TRACK AS THE STEERING RIDGE OVER THE PHILIPPINE SEA MOVES EASTWARD AND THE SYSTEM BEGINS TO MOVE INTO A WEAK AND COMPETING STEERING PATTERN. BY TAU 24, THE SYSTEM WILL SLOW DOWN TO BELOW FIVE KNOTS FORWARD SPEED AS IT RUNS INTO THE EASTERN SIDE OF A BAND OF STRONG NORTHEASTERLY FLOW ASSOCIATED WITH A COLD-SURGE STREAMING SOUTHWARD INTO THE SOUTH CHINA SEA (SCS) AND SIMULTANEOUSLY GETS TRAPPED BETWEEN RIDGING OVER THAILAND, OVER THE PHILIPPINE SEA AND A NEAR EQUATORIAL RIDGE (NER) TO THE SOUTH. TRACK SPEEDS WILL CONTINUE TO DECREASE AFTER TAU 24, WITH THE SYSTEM BECOMING QUASI-STATIONARY AFTER TAU 48. THE SYSTEM WILL LIKELY DRIFT TOWARDS THE SOUTHWEST, THEN SHIFT TO A MORE NORTHWARD DRIFT, ALBEIT AT VERY SLOW SPEEDS, AFTER TAU 72, AS THE RIDGE TO SOUTH BUILDS NORTHWARD AND ENHANCES THE STEERING GRADIENT ALONG THE EASTERN FLANK OF TS 33W. BY THE END OF THE FORECAST PERIOD, THE SYSTEM WILL BEGIN TURNING WESTWARD AS THE RIDGE TO THE NORTHWEST STRENGTHENS AND TAKES OVER THE PRIMARY STEERING INFLUENCE. IN TERMS OF INTENSITY, THE SYSTEM HAS A SHORT WINDOW OF 24 HOURS OF FAVORABLE CONDITIONS TO CONTINUE TO INTENSIFY, AND IS EXPECTED TO REACH A PEAK INTENSITY OF 70 KNOTS BEFORE THE DOOR SLAMS SHUT AND CONDITIONS RAPIDLY DETERIORATE, WITH RAPIDLY INCREASING SHEAR BEING THE PRIMARY NEGATIVE DRIVER. THE GREATLY ENHANCED SHEAR WILL LEAD TO A VORTEX DECOUPLING AND DECAPITATION, AND THE SYSTEM WILL QUICKLY WEAKEN DOWN TO ABOUT 45 KNOTS AS IT DRIFTS SLOWLY ACROSS THE SCS. THE WINDOW OF HIGH SHEAR WILL BE SHORT HOWEVER AND SHEAR WILL DECREASE AGAIN AFTER TAU 72, AND THE SYSTEM SEPARATES FROM THE COLD SURGE FLOW, ALLOWING FOR A RENEWED VORTEX ALIGNMENT AND REINTENSIFICATION AFTER TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS COME INTO SLIGHTLY BETTER AGREEMENT SINCE THE PREVIOUS MODEL RUN, THOUGH IT REMAINS HIGHLY UNCERTAIN AFTER TAU 48 IN PARTICULAR. UP TO TAU 48, ALL CONSENSUS MEMBERS ARE IN TIGHT AGREEMENT, BOTH IN THE ALONG- AND CROSS-TRACK SENSE, BUT THINGS GET A BIT SQUIRRELLY AFTER THIS POINT. THE MAJORITY OF THE JTWC MODIFIED CONSENSUS (WITHOUT THE UKMET, UKMET ENSEMBLE AND GALWEM) MEMBERS VERY SLOWLY TRACK THE SYSTEM SOUTHWESTWARD THEN NORTHWARD THROUGH THE END OF THE FORECAST PERIOD, WHILE THE ECMWF-AIFS AND GDM MEAN TURN THE SYSTEM NORTHWEST AT ABOUT DOUBLE THE SPEED. THE RESULT IS A FAIRLY WIDE CROSS-TRACK SPREAD BETWEEN THE COAST OF VIETNAM AND THE CENTRAL SCS. THE JTWC FORECAST IS POSITIONED JUST WEST OF THE CONSENSUS MEAN AFTER TAU 72, WITH LOW CONFIDENCE. INTENSITY GUIDANCE REMAINS IN GOOD OVERALL AGREEMENT, WITH ALL MODELS INDICATING A PEAK OCCURRING AT TAU 24, WITH A RANGE BETWEEN 60-75 KNOTS, FOLLOWED BY A STEADY WEAKENING AND THEN REINTENSIFICATION AFTER TAU 96. SEVERAL RI AIDS CONTINUE TO BE TRIPPED WITH THIS CYCLE, BUT WITH THE LIMITED WINDOW OF OPPORTUNITY FOR INTENSIFICATION, THE MORE AGGRESSIVE RIPA, RICN AND RIDE MEMBERS (PEAKING AT 95 KNOTS) ARE CONSIDERED UNLIKELY TO OCCUR. THE JTWC FORECAST IS PLACED ON THE HIGHER END OF THE ENVELOPE ACROSS THE MAJORITY OF THE FORECAST, WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN