MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 11W (NANGKA) WARNING NR 27// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 11W (NANGKA), LOCATED APPROXIMATELY 398 NM SOUTH-SOUTHEAST OF IWO TO, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. RECENT MSI CONTINUES TO SHOW A COMPACT DEEP CONVECTIVE CORE WITH A DISTINCT 11-NM DIAMETER EYE. THE CURRENT POSITION IS BASED ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 130 KNOTS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES NANGKA IS LOCATED IN AN AREA OF MODERATE VWS AND GOOD DIVERGENT OUTFLOW WITH AN EQUATORWARD BIAS. STY NANGKA IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP LAYERED SUB-TROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. STY 11W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH TAU 36 UNDER THE DOMINANT STEERING STR. MARGINAL CONDITIONS ARE EXPECTED TO BEGIN ITS WEAKENING TREND. NEAR TAU 36, STY NANGKA WILL SLOW AND BEGIN TO TURN POLEWARD TOWARDS A BREAK IN THE STEERING STR CAUSED BY A MID-LATITUDE TROUGH PASSING TO THE NORTH. VWS WILL FURTHER INCREASE DUE TO A TIGHTENED PRESSURE GRADIENT BETWEEN THE AFOREMENTIONED TROUGH AND A RIDGE BUILDING TO ITS WEST, FORCING STRONG NORTHERLY FLOW ALOFT. C. IN THE EXTENDED TAUS, STY 11W WILL TURN NORTHWESTWARD AGAIN AS A MID-LATITUDE RIDGE STRENGTHENS THE STEERING STR ALLOWING IT TO BUILD BACK OVER THE SYSTEM. HIGH VWS AND REDUCED OUTFLOW ALOFT WILL PERSIST THROUGH TAU 96. BEYOND TAU 96, THE UPPER LEVEL FLOW WILL BECOME IN-PHASE WITH THE CYCLONE, REDUCING THE VWS IMPACTS AND ALLOWING STY 11W TO RE-INTENSIFY THROUGH THE END OF THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE REMAINS GOOD AGREEMENT THROUGH TAU 72. DUE TO THE CONTINUED SPREAD IN THE MODEL SOLUTIONS AFTER 72 HOURS BECAUSE OF THEIR DEPICTION OF THE APPROACHING MID-LATITUDE TROUGH, THE JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.// NNNN NNNN