WDPN31 PGTW 200900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.5N 115.3E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 236 NM SOUTH-SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 22 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE CLASSIC SHRIMP-LIKE STRUCTURE OF AN ASYMMETRIC TROPICAL CYCLONE, WITH THE INITIAL POSITION PLACED AT THE HEAD OF THE SHRIMP, AND STRONG SOUTHERLY INFLOW FORMING THE TAIL. A 200527Z AMSR2 COLOR-ENHANCED 89GHZ IMAGE DEPICTED STRONG CONVECTIVE BANDING EXTENDING FROM SOUTH TO NORTHEAST OF THE CENTER AND SMALL INNER-CORE OF WEAKER CONVECTIVE BANDING FEATURES WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC), DEFINED BY A WEAK LOW EMISSIVITY REGION. ANIMATED WATER VAPOR IMAGERY AND CIMSS AMV ANALYSIS DEPICTS STRONG POLEWARD OUTFLOW INTO THE BASE OF A JET MAX EAST OF SHANGHAI, AND WEAKER EQUATORWARD OUTFLOW PUSHING SOUTH OVER THE PHILIPPINES. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON ANALYSIS OF THE MICROWAVE IMAGERY NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A BLEND OF OBJECTIVE AND SUBJECTIVE FIX ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE HOLDING STEADY, WITH STRONG OUTFLOW ALOFT, WARM SSTS, MODERATELY HIGH OHC AND LOW SOUTHERLY WIND SHEAR. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 45 KTS AT 200557Z CIMSS ADT: 43 KTS AT 200540Z CIMSS AIDT: 39 KTS AT 200540Z CIMSS D-MINT: 34 KTS AT 200529Z CIMSS D-PRINT: 35 KTS AT 200620Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: WEAK POLEWARD OUTFLOW. DRY MID-LEVEL AIR TO THE SOUTH. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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) 30W HAS CONTINUED TO TRACK NORTHWESTWARD ALONG THE SOUTHWESTERN SIDE OF THE STR OVER THE PAST 12 HOURS, THOUGH THE TRAJECTORY HAS SLOWLY BEEN TURNING MORE WESTWARD OVER THE LAST FEW HOURS BASED ON THE ANIMATED MSI. RIDGING IS BUILDING WESTWARD OVER SOUTHERN CHINA, WITH A SECONDARY STR CENTER DEVELOPING OVER NORTHERN VIETNAM. THE PRIMARY STEERING INFLUENCE WILL QUICKLY SHIFT TO THE EAST-WEST ORIENTED RIDGE OVER CHINA IN THE NEXT FEW HOURS, WITH TS 30W RAPIDLY TURNING DUE WEST IN RESPONSE. BY TAU 24 THE PRIMARY STEERING MECHANISM SHIFTS TO THE DEVELOPING RIDGE OVER NORTHERN VIETNAM, AND TS 30W WILL QUICKLY TURN TOWARDS THE SOUTHWEST AFTER TAU 24. STRONG NORTHEASTERLY FLOW EXCEEDING 35 KNOTS IS ALREADY PUSHING SOUTH OUT OF THE TAIWAN STRAIT, TRAPPED BETWEEN TS 30W AND THE SOUTHERN COAST OF CHINA, AS SEEN IN EARLIER SCATTEROMETER DATA. THESE ELEVATED, BUT RELATIVELY SHALLOW WINDS, WILL CONTINUE TO PUSH SOUTH OF HONG KONG OVER THE NEXT 12 HOURS, AND ACT LIKE A GUTTER-BUMPER AT THE BOWLING ALLEY, BLOCKING TS 30W FROM PUSHING MUCH FURTHER WEST AFTER TAU 24. THESE WINDS WILL ALSO ALIGN WITH THE MID-LAYER FLOW ASSOCIATED WITH THE DEEP RIDGE OVER VIETNAM, GIVING EVEN MORE IMPETUS FOR TS 30W TO QUICKLY TURN SOUTHWESTWARD. LANDFALL ALONG THE COAST OF VIETNAM, LIKELY BETWEEN HUE AND DA NANG, IS EXPECTED AROUND TAU 60, WITH THE REMNANTS OF TS 30W PUSHING FURTHER INLAND INTO LAOS OR EVEN CAMBODIA BY THE END OF THE FORECAST PERIOD. THE SYSTEM HAS SHOWN SIGNS OF IMPROVED ORGANIZATION OVER THE PAST 12 HOURS, FORMING WHAT APPEARS TO BE VERTICALLY ALIGNED VORTEX. THE ROBUST POLEWARD OUTFLOW WILL FUEL CONTINUED INTENSIFICATION FOR THE NEXT 24 HOURS, WITH THE SYSTEM REACHING A PEAK OF 60-65 KNOTS BEFORE LEVELING OFF. BY TAU 48, A MASSIVE INFLUX OF VERY DRY AND STABLE AIR IS FORECAST TO COMPLETELY ENGULF THE SYSTEM AND SMOTHER THE VORTEX, LEADING TO RAPID WEAKENING AS THE SYSTEM TRACKS TOWARDS VIETNAM. BY THE TIME THE SYSTEM MAKES LANDFALL, IT IS FORECAST TO BE A MINIMAL TROPICAL STORM AT BEST, WITH SOME MODELS SUGGESTING IT WONT EVEN MAKE IT TO THE COAST BEFORE DISSIPATING. AFTER MOVING INLAND, THE SYSTEM WILL DISSIPATE NO LATER THAN TAU 96, POTENTIALLY AS EARLY AS TAU 72. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD CROSS-TRACK AGREEMENT, WITH ALL MODELS CONTINUING TO CONCUR ON THE OVERALL TRACK SCENARIO. CROSS-TRACK SPREAD IS JUST 75NM AT TAU 36, INCREASING TO 105NM AT THE LANDFALL POINT. HOWEVER, ALONG-TRACK SPREAD IS MUCH HIGHER, PRIMARILY DUE TO THE COMPLETELY UNREALISTIC GFS AND GEFS, WHICH ARE RACING THE SYSTEM SOUTHWEST AT OVER 30 KNOTS, REACHING THE GULF OF THAILAND BY TAU 96. THE REMAINDER OF THE CONSENSUS MEMBERS DEPICT A MUCH MORE REALISTIC TRACK SPEED, GENERALLY CLOSE TO THE JTWC FORECAST POSITION, WHICH IS PLACED ON THE NORTHERN EDGE OF THE ENVELOPE, CLOSE TO THE ECMWF AND FNV3 TRACKERS. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH ALL CONSENSUS MEMBERS TIGHTLY PACKED ENVELOPE, PEAKING AT TAU 243 BETWEEN 55 KNOTS AND 60 KNOTS. TWO RAPID INTENSIFICATION (RI) AIDS, RIDE AND FRIA, CONTINUE TO BE TRIPPED, BUT WHILE CONDITIONS ARE FAVORABLE FOR INTENSIFICATION, THE PROBABILITY OF THE SYSTEM REACHING 85-100 KNOTS AS DEPICTED BY THE RI AIDS IS EXTREMELY LOW. ALL MEMBERS INDICATE THE INITIATION OF RAPID WEAKENING BY AFTER TAU 36, WITH DISSIPATION BETWEEN TAUS 72 AND 96. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN