WDPN31 PGTW 052100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 14W (KOINU) WARNING NR 026// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.9N 118.4E INITIAL INTENSITY: 70 KTS GEOGRAPHIC REFERENCE: 235 NM EAST OF HONG KONG MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 28 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TODAYS ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SIGNIFICANTLY SMALLER AND WEAKER TYPHOON (TY) 14W (KOINU) IN THE FAR SOUTHERN REACHES OF THE TAIWAN STRAIT. THE EIR SHOWS A CENTRAL DENSE OVERCAST WHICH HAS BEEN REDUCED TO ABOUT HALF OF THE SIZE IT WAS JUST 24 HOURS AGO. THE PREVIOUSLY STRONG EYE IS ALSO NO LONGER VISIBLE, HAVING FILLED IN AFTER MAKING LANDFALL. THE LAST MICROWAVE IMAGE RECEIVED WAS OVER 10 HOURS AGO, SO WE ARE RELIANT UPON RADAR IMAGERY FROM TAIWAN TO SEE UNDER THE HOOD AT WHAT IS GOING ON IN THE LOWER LEVELS. THE RADAR DATA DEPICTS A RAGGED EYE FEATURE, ROUGHLY 15NM WIDE AT ANALYSIS TIME BUT SHRINKING IN LATER IMAGERY, WITH WELL-DEFINED RAIN BANDS WRAPPING INTO THE CENTER. THIS DATA PROVIDED HIGH CONFIDENCE TO THE INITIAL POSITION. THE EYEWALL IS STRONGEST ON THE SOUTHERN SIDE, BUT THE LATEST RADAR DATA SUGGESTS THE EASTERN AND NORTHERN EYEWALL IS GETTING A BIT STRONGER. THE INITIAL INTENSITY OF 70 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE GENERAL AGREEMENT OF THE AGENCY FIXES AND THE CIMSS ADT, AIDT AND DPRINT ESTIMATES. THE LATEST CIMSS ANALYSIS SHOWS THAT THE SHEAR HAS DECREASED BY ABOUT HALF SINCE YESTERDAY, NOW ESTIMATED AT 11 KNOTS. AT THE SAME TIME, AS THE SYSTEM HAS BECOME MUCH SMALLER, IT HAS LOST ITS EQUATORWARD OUTFLOW CHANNEL AND THUS UPPER-LEVEL DIVERGENCE IS MUCH LESS THAN YESTERDAY, HELPING TO SUPPORT THE RAPID WEAKENING. ADDITIONALLY, WATER VAPOR IMAGERY SHOWS A WEDGE OF DRY AIR LYING IN WAIT ALONG THE CHINESE COASTLINE, SURGING SOUTHWARD DOWN THE WESTERN SIDE OF THE TAIWAN STRAIT, WHICH IS HELPING TO ERODE THE WESTERN PERIPHERY OF THE SYSTEM. OF NOTE, THE WIND RADII HAVE BEEN EXPANDED TO THE NORTHEAST TO ENCOMPASS THE GALE FORCE WINDS THAT EXTEND FROM THE NORTHERN PORTION OF THE TAIWAN STRAIT ALL THE WAY SOUTH INTO TY 14W. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHERN SIDE OF A SUBTROPICAL RIDGE (STR) AXIS THAT EXTENDS FROM THE GULF OF TONKIN TO EAST OF OKINAWA. OF NOTE, A NEAR EQUATORIAL RIDGE (NER) LIES NEAR THE BALABAC STRAIT. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS RJTD: T4.0 - 65 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 70 KTS AT 051749Z CIMSS ADT: 69 KTS AT 051730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: WEAK RADIAL 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: TY 14W IS FORECAST TO CONTINUE TRACKING TOWARDS THE WEST THROUGH THE NEXT 48 HOURS. HOWEVER, AS THE SYSTEM WILL SLOW SIGNIFICANTLY, TO JUST 2-3 KNOTS AFTER TAU 24, AS THE STR CENTER IN THE GULF OF TONKIN BUILDS, AND EFFECTIVELY SLOWS TO BLOCK FURTHER WESTWARD MOVEMENT. WITH ADDITIONAL WESTWARD MOTION BLOCKED, THE SYSTEM IS NOT EXPECTED TO MAKE LANDFALL, BUT WILL MAKE A CLOSE APPROACH TO HONG KONG AROUND TAU 48. IN TERMS OF INTENSITY, THE OVERALL ENVIRONMENT IS MARGINAL, IN THAT THERE ARE COMPETING AND OFFSETTING FACTORS INFLUENCING THE SYSTEM. THE LACK OF A STRONG OUTFLOW CHANNEL AND SMALL SIZE OF THE CDO IS HINDERING CONVECTIVE DEVELOPMENT SOMEWHAT, BUT THE GLOBAL MODEL FIELDS SUGGEST THE RADIAL OUTFLOW WILL REMAIN FIRMLY IN PLACE, IF WEAK, FOR THE NEXT 48 HOURS. VWS IS MUCH LOWER THAN 24 HOURS AGO, AND IS FORECAST TO REMAIN LOW THROUGH MOST OF THE FORECAST PERIOD. THIS COULD ALLOW FOR WHATEVER CONVECTION MAY FORM, TO PERSIST AND WRAP AROUND THE CORE. HINTS OF THIS ARE SEEN IN THE LATEST RADAR AND SATELLITE IMAGERY. OTHER FACTORS INCLUDE THE WARM SSTS, WHICH ALTHOUGH LOW IN HEAT CONTENT WILL ACTUALLY INHIBIT THE SYSTEM HAS IT SLOWS TO A CRAWL, WHILE UPWELLING COOLER WATERS. FINALLY, THE DRY AIR SURGING SOUTH ALONG THE CHINESE COAST WILL ERODE THE WESTERN SIDE OF THE INNER CORE AS THE SYSTEM APPROACHES THE COAST. ALL THESE FACTORS COMBINED WILL LEAD TO A SLOW WEAKENING TREND OF JUST FIVE KNOTS PER 12 HOURS THROUGH TAU 48, WITH A CHANCE OF A SHORT PERIOD OF STEADY INTENSITY IN THE NEXT 24 HOURS. AFTER TAU 48, THE UPWELLING AND INJECTION OF DRY CONTINENTAL AIR OFF THE COAST, ALONG WITH A SHIFT TO CONVERGENT FLOW ALOFT, WILL RESULT IN A MORE RAPID WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST. AND AS THE SYSTEM WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF LOW- TO MID-LEVEL NORTHEASTERLY FLOW OVER SOUTHERN CHINA, AND AS A RESULT KICK OUT TOWARDS THE SOUTHWEST AFTER TAU 72. THE SYSTEM IS FORECAST TO DISSIPATE AS A TROPICAL CYCLONE AS IT PASSES OVER HAINAN ISLAND BETWEEN TAU 96 AND TAU 120. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH TAU 72, WITH THE BULK OF THE MAJORITY OF THE CONSENSUS MEMBERS CONCURRING ON A SLOWING TRACK GENERALLY TOWARDS HONG KONG, THEN BECOMING NEARLY QUASI-STATIONARY FROM TAU 24 TO TAU 48. THE JGSM IS NOW THE ONLY MODEL SHOWING LANDFALL ALONG THE CHINESE COAST, THOUGH THE NAVGEM GETS CLOSE. THE JTWC FORECAST IS CONSISTENT WITH THE CONSENSUS MEAN THROUGH TAU 72, WITH MEDIUM CONFIDENCE. CONSISTENT WITH THE TRENDS OVER THE PAST COUPLE OF DAYS, THE MODELS RAPIDLY ACCELERATE THE SYSTEM SOUTHWESTWARD AFTER TAU 72, WITH A FAIR AMOUNT OF ALONG-TRACK SPREAD. THE GFS AND GEFS ENSEMBLE REMAIN THE FASTEST PAIR, POSITIONING THE SYSTEM NEAR THE VIETNAMESE COAST BY TAU 120, WHILE THE ECMWF, NAVGEM AND UKMET ENSEMBLE ARE MUCH SLOWER AND DISSIPATE THE SYSTEM NORTH AND EAST OF HAINAN. THE JTWC FORECAST IS CLOSE THE CONSENSUS TRACK BUT A FEW KNOTS SLOWER. DUE TO THE LARGE SPREAD IN THE GUIDANCE AFTER TAU 72, CONFIDENCE IS LOW IN THIS PORTION OF THE FORECAST. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A SLOW BUT STEADY WEAKENING TREND THROUGH TAU 48, FOLLOWED BY FASTER WEAKENING AND ULTIMATE DISSIPATION BY TAU 120, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: HIGH// NNNN