WDPN31 PGTW 282100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 017// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.9N 112.5E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 307 NM SOUTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS SIGNIFICANT WAVE HEIGHT: 19 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 33W CONTINUES TO DRIFT SLOWLY NORTHWARD, CAUGHT IN A WEAK AND COMPETING STEERING PATTERN. THE PRIMARY DRIVER PUSHING THE SYSTEM NORTHWARD IS THE RELATIVELY STRONGER STR TO THE PRODUCING A SLIGHTLY ENHANCED STEERING GRADIENT ALONG THE EASTERN SIDE OF THE SYSTEM, AND THE MODERATE MONSOONAL SOUTHWESTERLIES TO THE EASTERN FLANK OF THE SYSTEM. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT OVER THE PAST 6-12 HOURS, THE PREVIOUSLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) HAS TUCKED BACK UP UNDER THE SOUTHERN EDGE OF A RECENTLY DEVELOPED CENTRAL DENSE OVERCAST (CDO) FEATURE. HOWEVER, A 281749Z AMSR2 36GHZ MICROWAVE IMAGE REVEALED THE WELL-DEFINED LLCC TO BE FURTHER SOUTH THAN PREVIOUSLY ANALYZED, REQUIRING A LAST-MINUTE ADJUSTMENT IN THE BEST TRACK POSITION. THE MICROWAVE IMAGE ALSO REVEALED WELL-DEFINED CONVECTIVE BANDING FEATURES ALONG THE WESTERN PERIPHERY OF THE CIRCULATION, WRAPPING INTO THE SOUTHERN PORTION OF THE INNER CORE, THOUGH THE EASTERN SIDE IS MUCH WEAKER DUE TO THE PRESENCE OF MID-LEVEL DRY AIR IN THAT PORTION OF THE CIRCULATION. THE INITIAL POSITION IS ASSESSED WITH CONFIDENCE BASED ON THE ARCHER ANALYSIS OF THE AMSR2 IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, CONSISTENT WITH THE HIGHER AGENCY DVORAK CURRENT INTENSITY ESIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS HAVE IN GENERAL IMPROVED, WITH SHEAR DROPPING BELOW 10 KNOTS, HOWEVER DEEP-LAYER OUTFLOW HAS WEAKENED AND SIGNIFICANT UPWELLING HAS RESULTED IN MUCH COOLER SSTS IN VICINITY OF THE SLOW-MOVING SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, CAUGHT BETWEEN A SUBTROPICAL RIDGE (STR) OVER THE PHILIPPINE SEA AND AN STR OVER SOUTHERN MYANMAR. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.5 - 55 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS DEMS: T3.0 - 45 KTS CIMSS SATCON: 50 KTS AT 281758Z CIMSS ADT: 41 KTS AT 281730Z CIMSS AIDT: 33 KTS AT 281730Z CIMSS D-MINT: 37 KTS AT 281758Z CIMSS D-PRINT: 37 KTS AT 281900Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 25-26 CELSIUS OUTFLOW: WEAK POLEWARD AND EQUATORWARD OTHER FACTORS: DRY AIR ENTRAINMENT, PARTICULARLY ALONG THE EASTERN FLANK. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: AS IT IS SITUATED IN A WEAK AND COMPETING STEERING PATTERN, THE TRACK FORECAST FOR TS 33W IS FRAUGHT WITH UNCERTAINTY AND ERRATIC AND UNEXPECTED MOTION IS LIKELY OVER THE NEXT DAY OR TWO. OVERALL, GLOBAL MODELS ARE IN AGREEMENT THAT OVER THE NEXT DAY OR TWO, RIDGING WILL BUILD OVER LUZON AND ULTIMATELY EXTEND ALONG A NORTHEAST-SOUTHWEST AXIS FROM BORNEO TO LUZON. A LARGER BUT SLIGHTLY WEAKER RIDGE IS EXPECTED TO PERSIST OVER SOUTHERN MYANMAR AT THE SAME TIME. THE NET RESULT IS THAT TS 33W WILL TRACK VERY SLOWLY NORTHWARD AS THE STRONGEST STEERING GRADIENT WILL FACE THE RIDGE TO THE EAST. AFTER TAU 48, THE RIDGE OVER LUZON WILL SHIFT NORTHWESTWARD AND PUSH OUT INTO THE NORTHERN REACHES OF THE SOUTH CHINA SEA, WHICH WILL BLOCK TS 33W FROM ANY FURTHER NORTHWARD PROGRESSION AFTER TAU 48. AFTER REACHING AN INFLECTION POINT AROUND TAU 48, THE RIDGING TO THE WEST OVER MYANMAR WILL COME TO DOMINATE THE STEERING PATTERN, WITH THE PRIMARY AND STRONGEST STEERING GRADIENT SHIFTING TO THE WEST SIDE OF TS 33W. THE SYSTEM THEN RAPIDLY TURNS SOUTHWESTWARD, ACCELERATING THROUGH THE REMAINDER OF THE FORECAST PERIOD. LANDFALL IS EXPECTED ALONG THE COAST OF SOUTHERN VIETNAM BETWEEN TAU 96 AND TAU 120. IN TERMS OF INTENSITY, UPPER-LEVEL CONDITIONS ARE SET TO IMPROVE SLOWLY OVER THE NEXT 24 HOURS, WITH DECREASING SHEAR, IMPROVED OUTFLOW ALOFT AND INCREASING MOISTURE. HOWEVER, THE SLOW MOVEMENT OF TS 33W AND THE RESULTANT UPWELLING HAVE ROBBED IT OF AN ENERGY SOURCE, AND UNTIL IT MOVES FAR ENOUGH AWAY FROM THIS UPWELLED COLD POOL, THE LACK OF SUFFICIENT ENERGY WILL KEEP THE SYSTEM FROM INTENSIFYING TO ANY SIGNIFICANT DEGREE. BY TAU 48, THE SYSTEM SHOULD HAVE MOVED INTO SLIGHTLY WARMER WATERS, WHICH WILL ALLOW IT TO INTENSIFY BRIEFLY. AS IT TURNS SOUTHWESTWARD HOWEVER, TS 33W WILL SUCCUMB TO A SIGNIFICANT INFLUX OF DRY AIR AND INCREASINGLY EASTERLY SHEAR, WHICH WILL WEAKEN IT THROUGH AND AFTER LANDFALL. MODEL DISCUSSION: TRACK GUIDANCE IS WIDELY DISPERSED, ESPECIALLY AFTER TAU 48 AS THE SYSTEM REACHES THE INFLECTION POINT IN ITS TRACK. UP THROUGH TAU 48, ALL MODELS AGREE ON A SLOW NORTHWARD TRACK. THE NAVGEM IS SITUATED ON THE FAR WESTERN AND NORTHERN EDGE OF THE ENVELOPE, TRACKING THE LLCC ALL THE WAY INTO THE GULF OF THAILAND BY THE END OF THE FORECAST. THE ECMWF-AIFS MEANWHILE TURNS THE SYSTEM TO THE EAST, THEN SOUTHWESTWARD, POSITIONING IT ON THE FAR EASTERN EDGE OF THE GUIDANCE PACKAGE. THE RESULTING SPREAD BETWEEN OUTLIERS IS 550NM. THE REMAINDER OF THE CONSENSUS MEMBERS ARE RELATIVELY EVENLY SPACED BETWEEN THE TWO OUTLIERS, GENERATING A HIGH UNCERTAINTY IN THE FORECAST. THE JTWC FORECAST IS POSITIONED NEAR THE CONSENSUS MEAN AND HEDGED SLIGHTLY TOWARDS THE ECMWF DETERMINISTIC TRACKER. INTENSITY GUIDANCE IS SPLIT, WITH THE HAFS-A AND HWRF DEPICTING WEAKENING FROM THE START OF THE FORECAST, WHILE THE COAMPS-TC (BOTH VERSIONS) AND THE GFS SHOW INTENSIFICATION AFTER TAU 24, UP TO 65 KNOTS AT TAU 48. THE JTWC FORECAST IS PLACED NEAR OR SLIGHTLY ABOVE THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN