WDPN31 PGTW 292100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 021// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.7N 112.2E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 265 NM EAST-SOUTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 02 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL STORM (TS) 33W WITH A WEAK, COMPACT INNER-CORE OF MODERATE CONVECTION, WITH WEAKER CONVECTION FORMING INTO BANDS THAT ARE WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC). EARLIER ASCAT AND SAR PASSES INDICATE THAT THE LLCC REMAINS SMALL BUT WELL-DEFINED AND IS DRIFTING SLOWLY NORTHWARD. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE EARLIER ASCAT DATA ALONG WITH ANALYSIS OF THE EIR. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED TOWARDS THE LOWER END OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES IN LIGHT OF THE LOW (40 KNOT) SAR AND ASCAT MEASUREMENTS. WATER VAPOR IMAGERY AS WELL AS THE EIR AND HIGH-RESOLUTION MODEL CROSS-SECTION SUGGEST THAT THE ENVIRONMENT HAS MOISTENED OVERNIGHT, ESPECIALLY IN THE EASTERN FLANK, THROUGH SOME RESIDUAL MID-LEVEL DRY AIR IS STILL EVIDENT IN THE SOUTHEASTERN PORTION OF THE CIRCULATION. CIRA DERIVED MOTION VECTOR (DMV) UPPER-LEVEL ANALYSIS SUPPORTED BY WATER VAPOR IMAGERY, INDICATES A BURST OF RADIAL OUTFLOW EMANATING OUTWARD FROM THE CENTER, THOUGH AT PRESENT IT REMAINS RELATIVELY WEAK. SHEAR HAS DROPPED SIGNIFICANTLY OVER THE PAST SIX HOURS AS THE OUTFLOW HAS IMPROVED, WITH THE LATEST CIMSS SHEAR ESTIMATES DOWN TO 5-7 KNOTS. ADDITIONALLY, THE SYSTEM IS MOVING FURTHER AWAY FROM THE UPWELLING INDUCED COLD-POOL AND INTO WARMER WATERS. INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SAR DATA CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSION OF THE DEEP-LAYER SUBTROPICAL RIDGE (STR) OVER LUZON. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.5 - 55 KTS RCTP: T3.5 - 55 KTS KNES: T3.5 - 55 KTS DEMS: T3.0 - 45 KTS CIMSS SATCON: 50 KTS AT 291830Z CIMSS ADT: 47 KTS AT 291730Z CIMSS AIDT: 36 KTS AT 291730Z CIMSS D-MINT: 42 KTS AT 291439Z CIMSS D-PRINT: 40 KTS AT 291830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 33W HAS DRIFTED SLOWLY NORTHWARD OVER THE LAST 24 HOURS, AND CONTINUES TO DO SO, AS IT REMAINS TRAPPED IN A COMPETING STEERING PATTERN, WITH RIDGING DEVELOPING OVER LUZON AND RIDGING OVER SOUTHERN MYANMAR. THIS GENERAL SETUP IS EXPECTED TO PERSIST FOR ABOUT ANOTHER 24 HOURS AND THE SYSTEM WILL CONTINUE TO PUSH NORTHWARD AT ABOUT 2 KNOTS DURING THIS PERIOD. BY THIS POINT IN THE FORECAST, THE RIDGE PATTERN BEGINS TO SHIFT. FIRST THE RIDGE OVER LUZON PUSHES WESTWARD WHICH WILL HAVE THE EFFECT OF GIVING TS 33W A GENTLE NUDGE TOWARDS THE WEST AT TAU 36. THEN THE RIDGE OVER MYANMAR SHIFTS EASTWARD, BUILDS AND BECOMES THE DOMINATE STEERING INFLUENCE BY TAU 48. TS 33W REACHES THE INFLECTION POINT IN ITS TRACK AT TAU 24, SHIFTS WEST TO TAU 36 AND THEN TURNS SOUTHWEST BETWEEN TAU 36 AND TAU 48. THE SYSTEM ACCELERATES SOUTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD, MAKING LANDFALL ALONG THE SOUTHEASTERN COAST OF VIETNAM BETWEEN TAU 72 AND TAU 96. DUE TO THE IMPROVING ENVIRONMENTAL CONDITIONS, A BRIEF WINDOW OF OPPORTUNITY EXISTS FOR TS 33W TO INTENSIFY OVER THE NEXT 24-36 HOURS. WHILE CONDITIONS DO IMPROVE, THEY ARE NOT EXPECTED TO SUPPORT SIGNIFICANT INTENSIFICATION, PRIMARILY LIMITED BY RELATIVELY COOL SSTS (WARMER THAN THEY ARE CURRENTLY BUT STILL HOVERING AROUND 26C-27C). THE SYSTEM WILL PEAK OUT BETWEEN 50-55 KNOTS BY TAU 24, THEN HOVER AT THAT INTENSITY FOR ABOUT 12 HOURS BEFORE BEING SHELLACKED BY INCREASING SOUTHEASTERLY SHEAR AND DRY AIR ENTRAINMENT AS IT MOVES SOUTHWESTWARD TOWARDS LANDFALL. THE SYSTEM WILL WEAKEN BELOW TROPICAL STORM STRENGTH BY TAU 72, THEN DISSIPATE OVER SOUTHEASTERN VIETNAM BY TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS COME INTO BETTER AGREEMENT OVER THE LAST COUPLE OF RUNS, WITH ALL MODELS NOW AGREEING ON A NORTHWARD TRACK THROUGH TAU 24, THEN A TURN WEST FOLLOWED BY A TURN SOUTHWESTWARD. THERE REMAINS SOME DIFFERENCES IN THE EXACT TIMING OF THE TURNS AND THE AMOUNT OF ACCELERATION AFTER THE TURN OCCURS, LEADING TO SOME ENHANCED CROSS- AND ALONG-TRACK SPREAD, PARTICULARLY AFTER TAU 48. BY TAU 72, ALONG-TRACK SPREAD BETWEEN THE NAVGEM AND THE ECMWF OPENS UP TO 250NM, WITH ROUGHLY THE SAME AMOUNT OF CROSS-TRACK SPREAD. THESE VALUES INCREASE FURTHER BY THE END OF THE FORECAST PERIOD, WITH THE GFS AND ECMWF DEPICTING A MUCH SLOWER TRACK PROGRESSION AS COMPARED TO THE NAVGEM AND JGSM. THE JTWC FORECAST IS POSITIONED ON A BLEND OF THE ECMWF ENSEMBLE MEAN AND THE GDM ENSEMBLE MEAN, AND CONSISTENT WITH THE PREVIOUS FORECASTS. CONFIDENCE IS MEDIUM IN THE NEAR-TERM, TRENDING TO LOW IN THE EXTENDED FORECAST. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT THAT THE SYSTEM WILL INTENSIFY OVER THE NEXT 24-36 HOURS, WITH A RANGE OF PEAK INTENSITIES BETWEEN 45-55 KNOTS. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD 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