WDPN31 PGTW 202100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.6N 110.8E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 194 NM WEST-SOUTHWEST OF HONG KONG MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: XX FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL STORM (TS) 09W OVER LAND, CURRENTLY TRACKING JUST NORTH OF ZHANJIANG, CHINA. THE LIKELY CENTER IS BECOMING INCREASINGLY WELL-DEFINED AS THE SYSTEM CONTINUES WESTWARD OVER RELATIVELY FLAT TERRAIN, DECREASING THE FRICTIONAL EFFECTS, WHICH DISRUPTED THE VORTEX TO A HIGHER DEGREE. ANIMATED RADAR DATA INDICATES THE LOW LEVEL CIRCULATION CENTER (LLCC) IS STILL A BIT DISORGANIZED; HOWEVER THE OUTER RAIN BANDS ARE BECOMING STEADILY MORE DEFINED AND WRAPPING INTO THE CENTER. ANIMATED WATER VAPOR IMAGERY INDICATES STRONG EQUATORWARD OUTFLOW OVER THE GULF OF TONKIN, WHILE THE CIRA DERIVED MOTION WINDS PRODUCT SHOWS UPPER-LEVEL WINDS STREAMING SOUTHWESTWARD AT NEAR 40 KNOTS, PROVIDING AMPLE OUTFLOW TO SUPPORT CONVECTIVE DEVELOPMENT ONCE THE SYSTEM GETS BACK OVER WATER. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE RADAR DATA. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE DUE TO THE LACK OF RELIABLE INTENSITY ESTIMATES OVER LAND, THOUGH THE DPRINT AND RJTD FIX ARE GENERALLY CONSISTENT WITH THE ASSESSED INTENSITY. THE ENVIRONMENT IS, OVERALL, FAVORABLE FOR DEVELOPMENT ONCE THE SYSTEM REACHES THE WATER AGAIN. SHEAR REMAINS RELATIVELY HIGH; HOWEVER THE SHEAR VECTOR IS IN PHASE WITH THE STORM MOTION, AND THE OUTFLOW IS STRONG, WHICH WILL PARTIALLY COUNTERACT THE SHEAR. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A WEAK AND NARROW RIDGE LAYING ACROSS CENTRAL CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: NO CURRENT ESTIMATE RJTD: T3.0 - 45 KTS CIMSS D-PRINT: 53 KTS AT 201830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD OTHER FACTORS: OVER LAND FRICTIONAL EFFECTS. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: LOW INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 09W IS HAS TRACKED SLIGHTLY FURTHER NORTHWEST THAN ORIGINALLY EXPECTED OVER THE PAST FEW HOURS, THOUGH THIS IS NOT ANTICIPATED TO SIGNIFICANTLY ALTER THE FUTURE FORECAST TRACK. TS 09W WILL REACH THE FAR NORTHEASTERN CORNER OF THE GULF OF TONKIN WITHIN THE NEXT FEW HOURS, THEN BEGIN TO SLOW DOWN AS THE STEERING RIDGE TO THE NORTH BREAKS DOWN AHEAD OF A PASSING UPPER-LEVEL TROF. AFTER ENTERING THE GULF OF TONKIN, THE SYSTEM WILL SPEND ABOUT 24 TO 30 HOURS OVER THE WATER BEFORE MAKING LANDFALL OVER THE RED RIVER DELTA SOUTHEAST OF HANOI AROUND TAU 36. TRACK SPEEDS WILL INCREASE ONCE AGAIN AFTER LANDFALL AS A BUILDING RIDGE TO THE NORTHWEST BECOMES THE PRIMARY STEERING MECHANISM, AND THE SYSTEM WILL CONTINUE TO TRACK INLAND TO NORTHERN LAOS WHERE IT WILL ULTIMATE DISSIPATE. WITHOUT GOOD OBSERVATIONAL DATA, OR OVER LAND INTENSITY MEASUREMENTS, IT IS CHALLENGING TO ACCURATELY DETERMINE THE EXACT INTENSITY OF TS 09W AT THE CURRENT TIME. HOWEVER, IT APPEARS TO HAVE HELD TOGETHER RATHER NICELY AS IT SKIRTED THE COASTLINE DURING THE OVERNIGHT HOURS. WITH ONLY A FEW HOURS LEFT OVER LAND, IT IS LIKELY TO MAINTAIN ITS CURRENT INTENSITY THROUGH ITS RE-EMERGENCE BACK OVER WATER. ONCE IT MOVES FAR ENOUGH AWAY FROM THE COASTLINE TO ALLOW FOR THE WIND FIELD TO FLOW FREELY WITHOUT INFLUENCE OF LAND, THE STAGE WILL BE SET FOR IT TO INTENSIFY ONCE AGAIN. UPPER-LEVEL CONDITIONS LOOK TO REMAIN STEADY FOR THE DURATION OF THE SYSTEMS TRANSIT ACROSS THE GULF, WHERE THE WATERS ARE LIKE A BATHTUB, WITH SSTS EXCEEDING 31C IN SOME LOCATIONS. CONSEQUENTLY, IT IS LIKELY THE SYSTEM WILL INTENSIFY AT LEAST TO HIGH-END TROPICAL STORM STRENGTH AND POTENTIALLY BACK TO TYPHOON STRENGTH PRIOR TO LANDFALL IN VIETNAM. THE ONLY POTENTIAL HINDERANCE WILL BE THE MODERATE NORTHEASTERLY SHEAR AND HOW QUICKLY CONVECTION CAN REFORM AND COUNTERACT THE SHEAR. ONCE THE SYSTEM MOVES ASHORE IN VIETNAM, IT WILL RAPIDLY WEAKEN AND DISSIPATE OVER NORTHERN LAOS BY TAU 72. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE SHOWS STRONG CROSS-TRACK AGREEMENT THROUGH THE FORECAST PERIOD, AS THE MAIN GLOBAL MODELS CONCUR ON THE OVERALL RIDGE PATTERN. HOWEVER, THEY DISPLAY SHARP DISPARITIES IN THE ALONG-TRACK DIRECTION, WITH THE DIFFERENCES MOST PREVALENT BETWEEN THE GFS-GEFS AND THE ECMWF-ECEPS PAIRS. THE GFS, WHILE PLACING THE RIDGE TO THE NORTH GEOGRAPHICALLY IN THE SAME POSITION AS THE EUROPEAN MODELS, SHOWS SIGNIFICANTLY HIGHER RIDGE STRENGTH, THUS TS 09W TRAVERSES THE GULF OF TONKIN AT A HIGH RATE OF SPEED. THE ECMWF ON THE OTHER HAND SHOWS THE RIDGE BREAKING DOWN IN RESPONSE TO A TROF PASSAGE, WEAKENING THE STEERING GRADIENT AND ALLOWING TS 09W TO SLOW DOWN SHARPLY. BASED ON MODEL INITIALIZATION USING UPPER-AIR SOUNDINGS FROM ACROSS THE REGION, THE ECMWF APPEARS TO BE INITIALIZING MORE ACCURATELY AND THUS THE JTWC FORECAST HEAVILY FAVORS THE ECMWF TRACK THROUGH THE FORECAST PERIOD. INTENSITY GUIDANCE IS MIXED, WITH DECAY-SHIPS INDICATING RAPID WEAKENING FROM THE BEGINNING OF THE FORECAST. THE MESOSCALE MODELS ON THE OTHER HAND, INDICATE INTENSIFICATION ONCE OVER WATER THROUGH LANDFALL. THE HWRF IS THE MOST AGGRESSIVE, SHOWING A PEAK NEAR 85 KNOTS PRIOR TO LANDFALL WHEREAS THE HAFS-A AND COAMPS-TC ARE LESS AGGRESSIVE, FORECASTING A PEAK AROUND 55-60 KNOTS. THE FORECAST IS SET ON THE HIGHER END OF THE GUIDANCE PACKAGE BUT STILL WELL BELOW THE MOST AGGRESSIVE MODEL SOLUTIONS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN