WDPN31 PGTW 300300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 022// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.0N 112.4E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 266 NM EAST-SOUTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS MODERATE CONVECTION BEGINNING TO REDEVELOP NEAR THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC), AND WELL-DEFINED SPIRAL BANDING FEATURES WRAPPING INTO THE OBSCURED LLCC. A 292221Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS FRAGMENTED CONVECTION ISOLATED TO THE EASTERN FLANK OF THE CIRCULATION AND SHALLOW SPIRAL BANDS ON THE WESTERN FLANK, A REVERSAL IN THE OVERALL STRUCTURAL ORIENTATION COMPARED TO 24 HOURS AGO. ANIMATED WATER VAPOR AND CIMSS ATMOSPHERIC MOTION VECTORS (AMVS) DEPICT AN AREA OF DEEP, DRY AIR MOVING IN FROM THE NORTHWEST AND BEGINNING TO IMPINGE ON THE OUTER FRINGES OF TS 33W, ALONG WITH A BROAD ARC OF OUTFLOW PUSHING WELL OUT TO THE SOUTHEAST. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC REVEALED IN THE MICROWAVE IMAGE NOTED ABOVE AND ON TOP OF A VERY TIGHT GROUPING OF AGENCY FIX POSITIONS. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE MARGINAL, WITH COMPETING INFLUENCES. SHEAR IS LOW, BUT OUTFLOW IS WEAK, WHILE DRY AIR IS BEGINNING TO INTRUDE UPON THE NORTHWESTERN SIDE OF THE SYSTEM AND SSTS REMAIN RELATIVELY COOL DUE TO CONTINUED UPWELLING DUE TO THE VERY SLOW MOVEMENT OF THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, WITH THE STRONGEST INFLUENCE COMING FROM THE SUBTROPICAL RIDGE (STR) DEVELOPING OVER LUZON. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.5 - 55 KTS RCTP: T3.0 - 45 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 48 KTS AT 292300Z CIMSS ADT: 47 KTS AT 300030Z CIMSS AIDT: 37 KTS AT 300030Z CIMSS D-MINT: 44 KTS AT 292221Z CIMSS D-PRINT: 45 KTS AT 300020Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK RADIAL OTHER FACTORS: DRY AIR MOVING IN FROM THE NORTHWEST, UPWELLING OF COOLER WATERS. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 33W IS STILL CREEPING NORTHWARD, STUCK IN A WEAK AND COMPETING STEERING PATTERN, WITH RIDGING DEVELOPING OVER LUZON AND A RIDGE OVER SOUTHERN MYANMAR. THE RIDGING OVER LUZON IS STRENGTHENING AND SLOWLY IMPARTING A GREATER INFLUENCE ON THE TRACK OF TS 33W AND THIS TREND IS EXPECTED TO CONTINUE FOR THE NEXT 12 TO 24 HOURS. ONE MAJOR CHANGE TO THE FORECAST OF THIS RIDGE IS THAT IT IS NOW EXPECTED TO PUSH WESTWARD SOONER THAN PREVIOUSLY EXPECTED. THIS WILL PUSH TS 33W ONTO A WESTWARD TRACK EARLIER THAN THE PREVIOUS FORECAST, NOW EXPECTED TO REACH ITS FURTHEST NORTHWARD POINT WITHIN THE NEXT 12 HOURS, THEN TURN SHARPLY WESTWARD. AT THE SAME TIME, THE RIDGE OVER MYANMAR WILL BUILD AND SHIFT EASTWARD, MERGING WITH THE RIDGE OVER THE SOUTH CHINA SEA (SCS) WITHIN 24 HOURS. THE STEERING INFLUENCE THEN QUICKLY SHIFTS TO THE WESTERN RIDGE, AND TS 33W WILL TURN SHARPLY SOUTHWESTWARD SHORTLY AFTER TAU 24. THE SYSTEM WILL THEN SLOWLY PICK UP SPEED AS IT TRACKS TOWARDS THE COAST OF VIETNAM, WHERE LANDFALL IS EXPECTED SHORTLY AFTER TAU 72. COMPETING ENVIRONMENTAL PARAMETERS (LOW SHEAR, BUT WEAK UPPER-LEVEL OUTFLOW, MODESTLY WARM SSTS AND ENHANCED DRY AIR INTRUSION FROM THE NORTHWEST) WILL RESULT IN A STEADY INTENSITY THROUGH TAU 36, THOUGH SLIGHT DEVIATIONS BOTH HIGHER AND LOWER ARE POSSIBLE. AFTER TAU 36 HOWEVER, RAPIDLY INCREASING SHEAR, DRY AIR ENTRAINMENT INTO THE CORE OF THE SYSTEM AND REDUCED SSTS WILL CONSPIRE TO WEAKEN THE SYSTEM RAPIDLY AS IT APPROACHES LANDFALL. THE SYSTEM WILL BE A MINIMAL TROPICAL DEPRESSION AS IT MOVES ASHORE IN VIETNAM AND DISSIPATE OVER LAND SHORTLY THEREAFTER. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERAL AGREEMENT IN THE SHORT-TERM, WITH ALL MEMBERS OF THE GUIDANCE PACKAGE SHOWING A TRACK NORTHWARD THROUGH TAU 12 FOLLOWED BY A SHARP TURN WEST THEN SOUTHWEST. HOWEVER, THEY DO DIFFER STRONGLY ON THE PACE OF ACCELERATION AFTER THE TURN, AND BOTH ALONG- AND CROSS-TRACK SPREAD OPEN UP RAPIDLY AFTER TAU 36. BY TAU 48, CROSS- AND ALONG-TRACK UNCERTAINTY BOTH OPEN UP TO ABOUT 150NM. BY TAU 72, ALONG-TRACK SPREAD INCREASES TO ABOUT 300NM BETWEEN NAVGEM WHICH IS SITUATED OVER CAMBODIA AND THE GEFS MEAN JUST OFFSHORE OF VIETNAM, WHILE ALONG-TRACK SPREAD INCREASES TO ABOUT 275NM BETWEEN NAVGEM AND THE MUCH SLOWER GFS, ALONG OFFSHORE OF VIETNAM. UNCERTAINTY INCREASES STILL FURTHER THROUGH THE END OF THE FORECAST AS THE MODELS BEGIN TO LOSE TRACK OF THE VORTEX. THE JTWC FORECAST IS POSITIONED CLOSE TO THE ECMWF ENSEMBLE MEAN WITH MEDIUM TO LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH ALL GUIDANCE SAVE FOR THE DECAY-SHIPS (BOTH GFS AND NAVGEM) INDICATING STEADY INTENSITY FOR ABOUT THE FIRST 24 HOURS OR SO FOLLOWED BY A GENERAL WEAKENING TREND THEREAFTER. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN 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