MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 51// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 233 NM SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS DEGRADED AS CONVECTIVE BANDS WEAKENED. THE SYSTEM HAS ALSO LOST SYMMETRY EVEN AS IT MAINTAINED A RAGGED 35-NM EYE. THE INITIAL POSITION IS BASED ON THE MSI LOOP AND LINES UP WELL WITH A CENTRAL WARM SPOT ON THE 152211 37V SSMIS MICROWAVE IMAGE. THE INITIAL INTENSITY OF 70 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM ALL AGENCIES AND REFLECTS THE WEAKENING STAGE OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES A LESS FAVORABLE ENVIRONMENT WITH INCREASING VERTICAL WIND SHEAR (15-20 KNOTS). HOWEVER EXCELLENT DIVERGENT OUTFLOW CONTINUES TO PROVIDE VENTILATION TO THE WEAKENING CONVECTION. TY 11W IS TRACKING NORTH-NORTHWESTWARD UNDER AN EXTENSION OF THE STEERING SUB-TROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 11W WILL TRACK NORTH-NORTHWESTWARD ALONG THE WESTERN EXTENSION OF THE STEERING STR THROUGH TAU 24. AFTERWARDS, IT WILL RECURVE NORTHEASTWARD AS IT ROUNDS THE EDGE AND ACCELERATES ON THE POLEWARD SIDE OF THE STR. THE SYSTEM WILL MAKE LANDFALL OVER SHIKOKU SHORTLY AFTER TAU 12 WHICH WILL BEGIN A RAPID WEAKENING TREND DUE TO THE ADDITION OF LAND INTERACTION. AFTER TAU 24, TY 11W WILL EXIT INTO THE SEA OF JAPAN AS A WEAK TROPICAL STORM AND TURN TO THE NORTHEAST AS IT ROUNDS THE STR. THE RAPID DECAY WILL BE FURTHER EXACERBATED BY COLDER SSTS AND HIGH VWS. C. IN THE EXTENDED TAUS, TY NANGKA WILL CONTINUE TO ACCELERATE TO THE NORTHEAST AND CROSS THE NORTHERN TIP OF HONSHU NEAR MISAWA, AND BACK INTO THE PACIFIC OCEAN. POOR ENVIRONMENTAL CONDITIONS WILL CONTINUE TO WEAKEN THE SYSTEM LEADING TO ITS DISSIPATION BY THE END OF THE FORECAST PERIOD. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT OVER LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.// NNNN NNNN