WDPN32 PGTW 280300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 027// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 29.3N 130.1E INITIAL INTENSITY: 105 KTS GEOGRAPHIC REFERENCE: 229 NM SOUTH OF SASEBO, JAPAN MOVEMENT PAST 6 HOURS: NORTHWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 32 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A TYPHOON STRUCTURE THAT HAS DECAYED SOMEWHAT SINCE THE PREVIOUS WARNING. THE EYE HAS COOLED AND BECOME LESS CLOUD-FREE, COINCIDENT WITH A SLIGHT WARMING OF THE EYEWALL CLOUD TOPS AND COMPLETE EROSION OF THE WESTERN EYEWALL IN JAPANESE RADAR IMAGERY. THIS COULD BE DUE TO EARLY ONSET OF OCEANIC UPWELLING BENEATH THE STORM, COUPLED WITH THE IMPACTS OF ONGOING LIGHT TO MODERATE NORTHWESTERLY SHEAR, BUT OCEANIC COOLING IS DIFFICULT TO CONFIRM. THE STORM BRIEFLY SLOWED AND TOOK A NORTHWARD JOG DURING THE PAST SIX HOURS, WHICH MAY HAVE EXACERBATED ANY UPWELLING THAT IS OCCURRING. POLEWARD UPPER-LEVEL OUTFLOW HAS RECOVERED SOMEWHAT IN THE NORTHERN SEMICIRCLE IN RESPONSE TO THE TROUGH OVER THE SEA OF JAPAN, BUT OUTFLOW REMAINS CONCENTRATED PRIMARILY EASTWARD AND EQUATORWARD. THE INITIAL INTENSITY IS LOWERED TO 105 KT BASED ON A BLEND OF AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE ESTIMATES, ALONG WITH A 272112Z RCM-2 SAR IMAGE SHOWING A MAXIMUM SURFACE WIND ESTIMATE OF 107 KT. ONOAIDA, JAPAN LOCATED ABOUT 60 NM NORTH-NORTHEAST OF THE EYE IS CURRENTLY MEASURING SUSTAINED WINDS OF 48 KT. INITIAL WIND RADII BASIS: PERSISTENCE ADJUSTING FOR SURFACE OBSERVATIONS CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T6.0 - 115 KTS RCTP: T5.5 - 102 KTS KNES: T6.0 - 115 KTS CIMSS ADT: 112 KTS AT 272330Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TYPHOON 11W (SHANSHAN) CONTINUES TO MOVE LETHARGICALLY THROUGH THE RYUKYU ISLAND CHAIN. STEERING CURRENTS ARE WEAK AS THE TYPHOON IS MIRED JUST SOUTHEAST OF A COL IN THE DEEP-LAYER STEERING FLOW NEAR THE SOUTHERN KOREA PENINSULA. AN UPPER-LEVEL TROUGH OVER THE SEA OF JAPAN IS EXPECTED TO ALLOW SHANSHAN TO CONTINUE MAKING PROGRESS NORTH-NORTHWESTWARD OR NORTHWARD DURING THE NEXT 36 HOURS, BUT WILL THEN PULL OUT TO THE NORTHEAST, LEAVING THE STORM IN EVEN WEAKER STEERING CURRENTS. AT THIS POINT, MODELS GENERALLY AGREE THAT A VERY SLOW BUT SHARP TURN TOWARDS THE EAST WILL TAKE PLACE AS A WEAK RIDGE BUILDS IN SOUTHEAST OF THE TYPHOON, BRINGING SHANSHAN INLAND OVER KYUSHU BETWEEN 36 AND 48 HOURS. DURING THIS TURN, WIND SHEAR IS EXPECTED TO BE LOW, BUT OCEAN HEAT CONTENT VALUES DECREASE SIGNIFICANTLY IN THE WATERS SOUTH OF SASEBO RELATIVE TO WHERE SHANSHAN IS NOW. COMBINED WITH A SLOW FORWARD MOTION OF 5 KT OR LESS, THIS WILL RESULT IN MORE ACUTE OCEANIC COOLING BENEATH THE STORM THAN IS CURRENTLY OCCURRING, LEADING TO A MORE RAPID PACE OF WEAKENING JUST BEFORE LANDFALL. THE JTWC FORECAST SHOWS WEAKENING TO 80 KT PRIOR TO LANDFALL, BUT THE LANDFALL INTENSITY WILL BE SENSITIVE TO EXACTLY HOW LONG IT TAKES THE TYPHOON TO TRANSIT THE WATERS SOUTHWEST OF KYUSHU. AFTER LANDFALL, MODELS BEGIN TO DISAGREE SIGNIFICANTLY ON THE STORM'S TRACK DUE TO CONTINUING WEAK STEERING CURRENTS, WITH THE JET STREAM STAYING WELL NORTH OF THE STORM. A SECOND UPPER-LEVEL TROUGH IS EXPECTED TO BRIEFLY DIG INTO NORTHEASTERN CHINA AND SOUTHEASTERN RUSSIA IN ABOUT 72 HOURS, WHICH SOME MODELS LIKE GALWEM AND JGSM EXPECT TO BE STRONG ENOUGH TO USHER SHANSHAN NORTHEASTWARD INTO HONSHU. HOWEVER, THIS TROUGH ALSO EXITS QUICKLY, AND OTHER MODELS LEAVE SHANSHAN MAROONED SOUTH OF THE JETSTREAM EVEN AFTER THIS SECOND TROUGH PASSES, EITHER STALLING OR MOVING SLOWLY EASTWARD. THE GFS AND HAFS MODELS EVEN DEPICT A MEANDERING, LOOPING TRACK BACK WESTWARD OVER KYUSHU. THE JTWC FORECAST MAINTAINS A SLOW EAST-NORTHEASTWARD MOTION NEAR SHIKOKU DURING THE 72-120 HOUR PERIOD, BUT THERE IS HIGHER THAN AVERAGE UNCERTAINTY IN THE TRACK AFTER 48 HOURS, AND ERRATIC STORM MOTION IS POSSIBLE IN THE VICINITY OF KYUSHU AND SHIKOKU. THERE IS ALSO LOWER CONFIDENCE IN THE INTENSITY DURING THIS PORTION OF THE TRACK, AS THE STORM COULD REMAIN OVER LAND OR MOVE BACK OVER WATER SOUTH OF JAPAN FOR A TIME. HOWEVER, WEAKENING IS GENERALLY EXPECTED AFTER THE INITIAL LANDFALL DUE TO CONTINUING LAND INTERACTION AND THE PRESENCE OF DRY AIR AROUND THE STORM DEPOSITED BY THE PASSING UPPER-LEVEL TROUGHS. MODEL DISCUSSION: THE JTWC TRACK FORECAST IS A BIT SLOWER THAN THE MULTI-MODEL CONSENSUS, LEANING TOWARDS THE MORE RELIABLE MEMBERS SUCH AS ECMWF, GFS, EPS ENSEMBLE MEAN, GEFS ENSEMBLE MEAN WHICH ARE SLOWER THAN THE FAST OUTLIERS JGSM AND GALWEM. OVERALL, TRACK SPREAD NEAR JAPAN REMAINS IMMENSE, MAINLY IN THE ALONG-TRACK DIRECTION. THE JTWC INTENSITY FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS, BUT WITH LOW CONFIDENCE BEYOND 72 HOURS, PRIMARILY DUE TO THE WIDELY DISPARATE TRACK PREDICTIONS WHICH INFLUENCE THE INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN