WDPN31 PGTW 192100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.5N 116.0E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 111 NM EAST-SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 17 KTS SIGNIFICANT WAVE HEIGHT: 27 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LOPSIDED SYSTEM, WITH PRONOUNCED CONVECTIVE AREAS DISPLACED SOUTH OF A PARTIALLY OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). MINIMAL DEEP CONVECTIVE ACTIVITY IS OBSERVED ACROSS THE NORTHERN HEMISPHERE OF THE CIRCULATION. VORTICAL HOT TOWERS CONTINUE TO DEVELOP THE SOUTHERN PERIPHERY OF THE STORM, ROUGHLY ALONG THE RADIUS OF MAXIMUM WINDS (RMW). HOWEVER, DUE TO THE PERSISTENT MODERATE NORTHEASTERLY SHEAR, THESE VHTS HAVE BEEN UNABLE TO SUSTAIN UP-SHEAR PROPAGATION ON A PERSISTENT BASIS. A 191819Z NOAA-20 ATMS 89GHZ MICROWAVE IMAGE REVEALED SHALLOW BANDING FEATURES ACROSS THE NORTHERN PORTION OF THE ROTATION, WITH MORE SIGNIFICANT CONVECTIVE BANDING FEATURES TO THE SOUTH AND SOUTHEAST. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON ANALYSIS OF THE ANIMATED EIR, THE NOTED MICROWAVE IMAGE AND ANIMATED RADAR DATA FROM HONG KONG. RADAR IMAGERY SUGGESTS A DUE WEST TRACK SINCE APPROXIMATELY 1700Z, WITH THE LATEST FRAMES INDICATING THE POTENTIAL FORMATION OF A SMALL EYE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, ROUGHLY AT THE AVERAGE OF THE SUBJECTIVE DVORAK ESTIMATES FROM MULTIPLE AGENCIES, AS WELL AS THE OBJECTIVE ESTIMATES NOTED ABOVE. ENVIRONMENTAL CONDITIONS, WITH THE EXCEPTION OF SHEAR, REMAIN FAVORABLE. HOWEVER, PERSISTENT NORTHEASTERLY SHEAR (CURRENTLY ESTIMATED BY CIMSS AT 18 KNOTS) IS IMPEDING SIGNIFICANT INTENSIFICATION AND DEGRADING THE OVERALL ENVIRONMENTAL ASSESSMENT. OTHERWISE, SEA SURFACE TEMPERATURES (SSTS) ARE QUITE WARM, AND OUTFLOW IS STRONG TO THE SOUTHWEST. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSION OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.0 - 45 KTS RCTP: T3.5 - 55 KTS KNES: T4.0 - 65 KTS DEMS: T3.5 - 55 KTS CIMSS SATCON: 60 KTS AT 191731Z CIMSS ADT: 61 KTS AT 191730Z CIMSS AIDT: 52 KTS AT 191800Z CIMSS D-MINT: 55 KTS AT 191731Z CIMSS D-PRINT: 48 KTS AT 191830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: TROPICAL STORM (TS) 09W (WIPHA) IS FORECAST TO RAPIDLY SHIFT TO A MORE WESTWARD TRACK AND PASS SOUTH OF HONG KONG OVER THE NEXT 12 HOURS. RECENT RADAR DATA FROM HONG KONG INDICATES THIS TRACK SHIFT IS ALREADY UNDERWAY. THE SYSTEM IS EXPECTED TO MAKE LANDFALL TO THE WEST OF MACAU, NEAR THE MOUTH OF THE HUANGMAO RIVER BY TAU 12. SUBSEQUENTLY, TS 09W IS FORECAST TO TURN WEST-SOUTHWEST, SKIRTING THE CHINESE COAST AND REACHING THE VICINITY OF ZHANJIANG, CHINA BY TAU 24. THE SYSTEM WILL BEGIN TO SLOW AFTER THE INITIAL LANDFALL DUE TO FRICTIONAL EFFECTS. THIS DECELERATION WILL BE MORE PRONOUNCED AFTER TAU 24 AS THE EXTENSION OF THE RIDGE BREAKS DOWN TO THE NORTH DUE TO PASSAGE OF AN UPPER-LEVEL TROF. TS 09W IS FORECAST TO MOVE BACK OVER WATER, ENTERING THE NORTHERN GULF OF TONKIN BY TAU 36, BUT DUE TO THE WEAKENED STEERING PATTERN, TRACK SPEEDS WILL BE SIGNIFICANTLY SLOWER ONCE IT ENTERS THE GULF. THE PRIMARY STEERING INFLUENCE JUMPS FROM THE RIDGE TO THE EAST TO A DEEP-LAYER RIDGE OVER THE TIBETAN PLATEAU AFTER TAU 48, STRENGTHENING THE STEERING GRADIENT, PROVIDING AN IMPETUS FOR TS 09W TO ACCELERATE WESTWARD. A SECOND LANDFALL IS FORECAST AROUND TAU 60, NEAR THE RED RIVER DELTA SOUTHEAST OF HANOI, VIETNAM. AFTER LANDFALL, THE SYSTEM WILL CONTINUE TRACKING INLAND THROUGH THE END OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, TS 09W IS FORECAST TO INTENSIFY SLIGHTLY OVER THE NEXT 12 HOURS, WITH A PEAK INTENSITY OF 60 KNOTS EXPECTED AS THE SYSTEM MAKES LANDFALL. DUE TO FRICTIONAL EFFECTS AND TERRAIN INTERACTIONS, THE SYSTEM WILL WEAKEN SHARPLY THROUGH TAU 24 AS IT SKIRTS THE COASTLINE. AS IT MOVES BACK OVER WATER IN THE GULF OF TONKIN, THE SLOWER SPEEDS AND SLIGHTLY IMPROVED UPPER-LEVEL CONDITIONS (LOWER SHEAR AND INCREASED EQUATORWARD OUTFLOW), WILL FACILITATE RAPID INTENSIFICATION, CAPITALIZING ON THE VERY WARM (30-31C) SSTS IN THE GULF OF TONKIN. THE FORECAST CALLS FOR A PEAK OF 55 KNOTS AT TAU 48, HOWEVER IT IS POSSIBLE THE ACTUAL PEAK COULD BE SLIGHTLY HIGHER, OCCURRING IMMEDIATELY PRIOR TO LANDFALL, EXPECTED NEAR TAU 60. REGARDLESS, ONCE THE SYSTEM MAKES LANDFALL, IT WILL RAPIDLY WEAKEN AS IT TRAVERSES FURTHER INLAND, ULTIMATELY DISSIPATING OVER NORTHERN LAOS NO LATER THAN TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE EXHIBITS STRONG AGREEMENT, PARTICULARLY IN THE CROSS-TRACK REALM, THROUGH THE ENTIRE FORECAST PERIOD. FAIRLY LARGE ALONG-TRACK DIFFERENCES BEGIN TO APPEAR AROUND TAU 36, AND ARE PARTICULARLY EVIDENT BETWEEN THE GFS-GEFS AND THE ECMWF-ECEPS-ECAIFS COMBINATIONS. THE GFS-GEFS IS CONSIDERABLY FASTER, INDICATING LANDFALL IN VIETNAM AT OR BEFORE TAU 48, WHILE THE ECMWF SERIES INDICATE A MUCH SLOWER TRACK ACROSS THE GULF OF TONKIN. ADDITIONALLY, AFTER TAU 48, THE GFS-GEFS COMBO SHOW THE SYSTEM TURNING SHARPLY BACK TO THE SOUTHEAST AND MOVING BACK OVER HAINAN ISLAND. NO OTHER MODEL EXHIBITS THIS BEHAVIOR, THUS INTRODUCING SIGNIFICANT UNCERTAINTY IN THE GFS-GEFS SOLUTIONS. THE JTWC FORECAST IS CONSISTENT WITH THE ECMWF-ECEPS-ECAIFS SOLUTIONS THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT, ALTHOUGH THE JTWC FORECAST DEVIATES SLIGHTLY HIGHER THROUGH TAU 12, THEN REJOINS THE PACK CONSENSUS BY TAU 12. ALL CONSENSUS MEMBERS INDICATE THE SYSTEM WILL MAINTAIN OR INTENSIFY BETWEEN TAU 24 AND 48, FOLLOWED BY RAPID WEAKENING. THE JTWC FORECAST IS ABOUT 10 KNOTS HIGHER THAN THE HAFS-A AND ABOUT 5 KNOTS LOWER THAN THE HWRF, THOUGH ABOUT 20 KNOTS HIGHER THAN THE CONSENSUS MEAN AT TAU 48 DUE TO THE INFLUENCE OF THE MUCH LOWER DECAY-SHIPS OUTPUT. INTENSITIES WILL BE LARGELY DRIVEN BY HOW FAR INLAND THE SYSTEM TRACK THROUGH TAU 24 AND HOW MUCH IT SLOWS AFTER TAU 24, SO CONFIDENCE IS SET TO LOW THOUGH THE FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN