WDPN31 PGTW 200300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (WIPHA) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.6N 114.6E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 48 NM SOUTH-SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 29 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TYPHOON (TY) 09W (WIPHA) HAS RAPIDLY CONSOLIDATED AND INTENSIFIED OVER THE PAST SIX HOURS AS IT PASSES SOUTH OF HONG KONG. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTED AN EXPLOSIVE BURST OF DEEP CONVECTION, WHICH BEGAN JUST PRIOR TO THE 200000Z HOUR, SUBSEQUENTLY EXPANDING AND COVERING THE ASSESSED LOW LEVEL CIRCULATION CENTER. FORTUNATELY, THE SYSTEMS CLOSE PROXIMITY TO HONG KONG ALLOWS RADAR TO PROVIDE VALUABLE INSIGHTS INTO THE OTHERWISE OBSCURED INNER STRUCTURE. THE RADAR EYE HAS SIGNIFICANTLY DECREASED IN SIZE OVER THE LAST COUPLE OF HOURS, WITH DEEP CONVECTION FORMING A PARTIAL EYEWALL ALONG THE SOUTHERN HALF OF THE RADAR EYE. THE NORTHERN SIDE REMAINS SIGNIFICANTLY WEAKER, LIKELY A RESULT OF THE PERSISTENT NORTHEASTERLY SHEAR, CURRENTLY ESTIMATED AT ABOUT 16 KNOTS. OFFICIAL SURFACE OBSERVATIONS FROM THE VICINITY OF HONG KONG INDICATE SUSTAINED GALE TO STORM-FORCE WINDS AND PRESSURES (AT SHORE STATIONS) OF AROUND 980MB, WHILE UNOFFICIAL OBSERVATIONS SUGGEST THE POTENTIAL FOR HIGHER WINDSPEEDS AND LOWER PRESSURES. A 192006Z GMI COLOR-ENHANCED 37GHZ MICROWAVE IMAGE DEPICTED A SOLID CYAN RING FEATURE, INDICATING THE SYSTEM WAS PRIMED FOR POSSIBLE RAPID INTENSIFICATION. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE RADAR EYE FEATURE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE OVERALL AVERAGE OF THE OBJECTIVE ESTIMATES NOTED ABOVE AND SLIGHTLY EXCEEDING THE BULK OF THE SUBJECTIVE, AGENCY DVORAK CURRENT INTENSITY ESTIMATES. THE ENVIRONMENT IS, IN THE AGGREGATE, FAVORABLE FOR FURTHER INTENSIFICATION, WITH WARM SSTS, AND GOOD EQUATORWARD OUTFLOW, OFFSET SOMEWHAT BY THE MODERATE NORTHEASTERLY SHEAR. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN 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: T3.5 - 55 KTS RCTP: T3.5 - 55 KTS KNES: T4.0 - 65 KTS DEMS: T3.5 - 55 KTS CIMSS SATCON: 64 KTS AT 192230Z CIMSS ADT: 60 KTS AT 200000Z CIMSS AIDT: 64 KTS AT 200100Z CIMSS D-MINT: 66 KTS AT 192022Z CIMSS D-PRINT: 63 KTS AT 200030Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD 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: TY 09W IS, AS PREVIOUSLY FORECAST, NOW TRACKING DUE WEST ALONG THE SOUTHWESTERN SIDE OF AN EXTENSION OF THE STR TO THE NORTHEAST. THE SYSTEM IS EXPECTED TO MAKE LANDFALL IN THE VICINITY OF YANGJIANG, CHINA WITHIN THE NEXT 12 HOURS, THEN TURN SOUTHWESTWARD, SKIRTING THE COASTLINE OF SOUTHERN CHINA. THE SYSTEM WILL PASS IN CLOSE PROXIMITY TO ZHANJIANG AND BE MOVING BACK OVER OPEN WATERS OF THE FAR NORTHEASTERN GULF OF TONKIN BY TAU 24. THE FORWARD SPEED OF TY 09W IS FORECAST TO BEGIN DECELERATING AFTER LANDFALL, DUE TO FRICTIONAL EFFECTS AS IT INTERACTS WITH THE TERRAIN. AFTER TAU 24, THE WEAKENING OF THE RIDGE TO THE NORTH DUE TO PASSAGE OF AN UPPER-LEVEL TROF, WILL RESULT IN A WEAKER STEERING GRADIENT AND MORE SIGNIFICANT SLOWDOWN AS THE SYSTEM MOVES INTO THE GULF OF TONKIN. THE SLOWDOWN WILL ONLY LAST ABOUT 24 HOURS. HOWEVER, AS ANOTHER STRONG RIDGE OVER THE TIBETAN PLATEAU BUILDS IN FROM THE WEST AND STRENGTHENS THE STEERING GRADIENT, TY 09W WILL ONCE AGAIN PICK UP SPEED AFTER TAU 48 AS IT APPROACHES A SECOND LANDFALL OVER THE RED RIVER DELTA SOUTHEAST OF HANOI, VIETNAM. IN TERMS OF INTENSITY, THE SYSTEM HAS CLEARLY CAPITALIZED ON THE SHALLOW WARM WATERS ALONG THE CHINESE COAST AND SUCCESSFULLY COUNTERED THE MODERATE SHEAR. TY 09W IS LIKELY TO INTENSIFY A BIT FURTHER PRIOR TO LANDFALL, THOUGH THE PROXIMITY TO THE COASTLINE WILL LIKELY SERVE TO TEMPER THE INTENSIFICATION SOMEWHAT AS IT GETS CLOSER TO THE COAST. THE FORECAST CURRENTLY CALLS FOR A PEAK OF 70 KNOTS AS THE SYSTEM HITS THE COAST, BUT IT IS POSSIBLE IT COULD REACH A SLIGHTLY HIGHER PEAK IF THE CONVECTION ALL REMAINS OFFSHORE FOR A BIT LONGER. AS IT SKIRTS THE COAST, THE SYSTEM WILL WEAKEN SIGNIFICANTLY DUE TO FRICTIONAL EFFECTS AND IS FORECAST TO STILL BE A STRONG TROPICAL STORM WHEN IT MOVES BACK OVER THE GULF OF TONKIN. ONCE OVER WATER AGAIN, THE SYSTEM IS FORECAST TO REINTENSIFY RATHER QUICKLY, UP TO 60-65 KNOTS AS IT MOVES ACROSS VERY WARM (30-31C) WATERS AND MAINTAINS A RELATIVELY FAVORABLE UPPER- LEVEL ENVIRONMENT OF MODERATE SHEAR AND GOOD EQUATORWARD OUTFLOW. ONCE ASHORE IN VIETNAM, THE SYSTEM WILL RAPIDLY WEAKEN AND ULTIMATELY DISSIPATE OVER THE MOUNTAINS OF NORTHERN LAOS NO LATER THAN TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH MOST OF THE FORECAST PERIOD, WITH MINIMAL CROSS- OR ALONG-TRACK UNCERTAINTY THROUGH THE EARLY PORTION OF THE FORECAST. CROSS-TRACK UNCERTAINTY REMAINS FAIRLY CONSISTENT THROUGH THE MID- AND EXTENDED-RANGE FORECAST, BUT ALONG-TRACK SPREAD BEGINS TO APPEAR AS EARLY AS TAU 36, WHEN THE GFS-GEFS COMBINATION STARTS TO DIVERGE FROM THE REMAINDER OF THE MODELS. THE GFS MODELS INDICATE A LANDFALL IN VIETNAM AS EARLY AS TAU 48, WHILE THE REMAINDER OF THE PACKAGE ARRIVES ABOUT 12-18 HOURS LATER. AFTER LANDFALL, THE ECMWF-ECEPS-ECAIFS COMBINATION REJOINS THE GFS BEFORE THE MODELS DISPERSE AS THE SYSTEM WEAKENS AND VORTEX IS LOST. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS TRACK AND THE ECMWF TRACKER THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS MIXED. ONLY THE DECAY-SHIPS (GFS) INDICATES ANY SORT OF NEAR-TERM INTENSIFICATION, WHILE THE HAFS-A AND CONSENSUS MEAN SHOW STEADY BUT RELATIVELY SLOW WEAKENING TO TAU 24. CONVERSELY, THE GFS AND HWRF SHOW RAPID WEAKENING TO JUST 40 KNOTS BY TAU 12, FOLLOWED BY RAPID INTENSIFICATION IMMEDIATELY AFTER. MOST OF THE MODELS SHOW SOME DEGREE OF REINTENSIFICATION IN THE GULF OF TONKIN, THOUGH THERE IS A SIGNIFICANT AMOUNT OF UNCERTAINTY IN THE ACTUAL PEAK. THE JTWC FORECAST IS POSITIONED ABOUT 10 KNOTS HIGHER THAN THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. THE EXTENT TO WHICH THE SYSTEM PENETRATES INLAND IN THE SHORT TERM WILL HAVE A SIGNIFICANT IMPACT ON THE ULTIMATE INTENSITY AND THUS THE CONFIDENCE IN THE INTENSITY FORECAST IS MEDIUM TO LOW. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW//// NNNN