MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 05W (GUCHOL) WARNING NR 28// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 05W (GUCHOL), LOCATED APPROXIMATELY 350 NM SOUTH OF KADENA AB, OKINAWA, HAS TRACKED NORTHWARD AT 11 KNOTS OVER THE PAST SIX HOURS. TY 05W HAS RECENTLY BEEN DOWNGRADED FROM SUPER TYPHOON STATUS TO TYPHOON. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM HAS STARTED TO SHOW SIGNS OF WEAKENING AS THE EYE DIAMETER HAS SLOWLY DECREASED OVER THE PAST SIX HOURS FROM 15 NM TO 10 NM AND IS BECOMING MORE RAGGED. THE DEEPEST CONVECTION REMAINS ON THE SOUTHERN HALF OF THE SYSTEM, BUT CONVECTION ALONG THE NORTHWESTERN QUADRANT HAS STARTED TO WEAKEN SLIGHTLY OVER THE PAST SIX HOURS. THE EYEWALL REPLACEMENT CYCLE (ERC) HAS FINISHED WITH NO IDENTIFIABLE IMPACT TO THE OVERALL INTENSITY. TY 05W HAS SHIFTED TO A NORTHWARD TRACK AT THE WARNING TIME, AND SINCE ISSUING WARNING NUMBER 28, EIR IMAGERY IS INDICATING A SLIGHT TURN TO THE EAST-NORTHEAST AS TY 05W APPEARS TO HAVE STARTED TO TRACK AROUND THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) AXIS. THE CURRENT POSITION IS BASED ON THE EYE IN EIR AND AGREES WITH PGTW FIX. THE CURRENT INTENSITY IS SLIGHTLY DECREASED TO 125 KNOTS BASED ON A 6.0/6.5 DVORAK FIX FROM PGTW AND A 5.0/5.5 FROM RJTD BOTH SHOWING A SLIGHT WEAKENING TREND. THIS AGREES WITH THE OBSERVED WEAKENING TREND NOTED IN EIR. UPPER-LEVEL ANALYSIS INDICATES THE MESOSCALE ANTICYCLONE REMAINS SLIGHTLY DISPLACED LOW-LEVEL CIRCULATION CENTER (LLCC). THIS FEATURE CONTINUES TO VENT THE SYSTEM ALONG THE EQUATORWARD OUTFLOW CHANNEL. THE POLEWARD CHANNEL HAS YET TO TAP INTO THE STRONG UPPER-LEVEL JET. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 05W IS EXPECTED TO CONTINUE TRACKING TO THE EAST-NORTHEAST AROUND THE NORTHWESTERN PERIPHERY OF THE STEERING STR. AN UPPER-LEVEL TROUGH LOCATED OVER EASTERN CHINA IS EXPECTED TO MODIFY THE STR FURTHER AS TY 05W TRACKS TOWARDS JAPAN. MODEL GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH TAU 36, SHOWING TY 05W GRADUALLY WEAKENING AS THE OVERALL ENVIRONMENT DETERIORATES. THE WEAKENING TREND WILL BEGIN SLOWLY AS VERTICAL WIND SHEAR (VWS) INCREASES AS TY 05W APPROACHES THE MID-LATITUDE FRONTAL BOUNDARY ASSOCIATED WITH A LOW PRESSURE CIRCULATION CURRENTLY LOCATED OVER NORTHEAST CHINA. AS THE LOW MOVES TOWARDS THE SEA OF JAPAN BETWEEN TAU 24 AND 36, THE VWS IS EXPECTED TO FURTHER WEAKEN TY 05W. SEA SURFACE TEMPERATURES (SSTS) HAVE BEEN FAVORABLE TO THIS POINT; HOWEVER, THEY WILL SLOWLY DECREASE OVER THE NEXT 12 TO 24 HOURS, GOING FROM 29 CELSIUS TO APPROXIMATELY 24 TO 26 CELSIUS BY TAU 24. BEYOND TAU 24 SSTS REMAIN VERY UNFAVORABLE. THE MAJOR CONCERN WITH THE FORECAST IS BEYOND TAU 36. THE FORECAST KEEPS THE TRACK TO THE WEST OF TOKYO AS THE SYSTEM UNDERGOES EXTRA-TROPICAL TRANSITION (ETT). MODEL GUIDANCE CONTINUES TO INDICATE A TRACK OVER KYOTO INTO THE SEA OF JAPAN. THE THOUGHT PROCESS FOR THE FORECAST IS THAT MODEL GUIDANCE IS TRACKING TOWARDS THE MID-LEVEL VORTICITY FIELDS, WHILE THE LLCC IS EXPECTED TO TRACK ALONG THE STATIONARY FRONTAL BOUNDARY LOCATED ALONG COASTAL JAPAN. LAND EFFECTS ON THE LLCC DURING THE ETT PROCESS WILL CREATE A VERY DISORGANIZED STRUCTURE BETWEEN TAU 48 AND 72. THERE IS HIGH CONFIDENCE IN THE FORECAST TRACK THROUGH TAU 36, BUT DECREASES TO LOW BEYOND TAU 36 AS THE FORECAST TRACK DIFFERS FROM THE MAJORITY OF MODEL GUIDANCE WITHIN THE CONSENSUS.// NNNN NNNN