MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 32// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 355 NM SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED SOUTHEASTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY INDICATES AN ONGOING WEAKENING TREND DUE TO INCREASING VERTICAL WIND SHEAR ASSOCIATED WITH EQUATORWARD OUTFLOW FROM TY 16W. THIS INTERACTION IS CLEARLY EVIDENT IN RECENT ANIMATED WATER VAPOR IMAGERY. AS A RESULT OF THE EASTERLY VERTICAL WIND SHEAR, CONVECTIVE ORGANIZATION HAS DEGRADED AND THE CENTER HAS BECOME MORE DIFFICULT TO DISCERN IN SATELLITE IMAGERY; HOWEVER, RADAR FIXES ARE AVAILABLE FROM MULTIPLE AGENCIES. THE INITIAL POSITION IS BASED ON ANIMATED ENHANCED INFRARED IMAGERY AND AVAILABLE RADAR FIXES WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 85 KNOTS BASED ON AN AVERAGE OF DVORAK INTENSITY ESTIMATES RANGING FROM 77 TO 90 KNOTS FROM PGTW AND RJTD, RESPECTIVELY. TY 15W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT BETWEEN A WEAK SUBTROPICAL RIDGE (STR) TO THE NORTH AND A BUILDING NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH. ADDITIONALLY, THERE MAY BE SOME WEAK INTERACTION OCCURRING WITH TY 16W, WHICH IS CENTERED APPROXIMATELY 695 NM EAST- NORTHEAST OF TY 15W'S CENTER. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 15W IS FORECAST TO REMAIN WITHIN THIS WEAK STEERING ENVIRONMENT THROUGH TAU 12 AND WILL TRACK INCREASINGLY NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE NER, WHICH IS FORECAST TO BUILD TO THE EAST AS TY 16W TRACKS QUICKLY POLEWARD INTO THE YELLOW SEA. THIS WILL ALLOW TY 15W TO TURN POLEWARD AND ACCELERATE JUST EAST OF, OR POSSIBLY OVER TAIWAN. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT WITH A 250+ NM SPREAD AT TAU 72. THE JTWC FORECAST IS POSITIONED CLOSE TO THE MODEL CONSENSUS BUT FAVORS THE ECMWF AND JGSM SOLUTIONS, WHICH HAVE BEEN VERY CONSISTENT. THE GFS MODEL IS THE MAJOR OUTLIER, WITH A NORTHEASTERLY TRACK INTO THE YELLOW SEA. TY 15W IS FORECAST TO GRADUALLY WEAKEN THOUGH TAU 48 DUE TO ONGOING INTERACTION WITH LAND AND MODERATE VERTICAL WIND SHEAR. THE INTENSITY FORECAST IS BASED ON AN EAST-OF-TAIWAN FORECAST, HOWEVER, A SLIGHT WESTWARD SHIFT IN TRACK COULD FURTHER DEGRADE THE INTENSITY. THE SYSTEM IS FORECAST TO MAKE LANDFALL SOUTHEAST OF SHANGHAI, CHINA NEAR TAU 72. C. AFTER TAU 72, TY 15W IS FORECAST TO TRACK NORTHWARD ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TOWARD THE SHANGHAI REGION. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT WITH A LARGE SPREAD AT TAU 120. GFDN IS THE WESTERN-MOST OUTLIER WHEREAS GFS IS NOW THE EASTERN-MOST OUTLIER WITH A POLEWARD TRACK OVER THE KOREAN PENINSULA. THE JTWC FORECAST FAVORS THE ECMWF SOLUTION AND REMAINS CONSISTENT WITH PREVIOUS WARNINGS. TY 15W IS EXPECTED TO WEAKEN AS IT MOVES OVER LAND AND SHOULD DECREASE TO 30 TO 35 KNOTS BY TAU 120. BASED ON THE COMPLEX AND WEAK STEERING PATTERN AS WELL AS POSSIBLE WEAK INTERACTION WITH TY 16W, THERE IS LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN