WDPN33 PGTW 091500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 11W (NANGKA) WARNING NR 25// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 11W (NANGKA), LOCATED APPROXIMATELY 182 NM NORTH-NORTHWEST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS A COMPACT CENTRAL CONVECTIVE CORE WITH A DISTINCT EYE FEATURE THAT HAS CONTRACTED TO 8-NM; PROVIDING HIGH CONFIDENCE IN THE CURRENT POSITION. THE INITIAL INTENSITY HAS BEEN INCREASED TO 135 KNOTS BASED ON AGENCY DVORAK INTENSITY ESTIMATES RANGING FROM 127 TO 140 KNOTS AND SUPPORTED BY A PRONOUNCED INTENSIFICATION IN THE CONVECTIVE RING COMPLETELY SURROUNDING THE EYE, WHICH CAN BE SEEN IN THE 090912Z SSMIS 91GHZ MICROWAVE IMAGE. UPPER LEVEL ANALYSIS INDICATES A MOSTLY FAVORABLE ENVIRONMENT WITH MODERATE (15- 20 KNOTS) NORTHWESTERLY VERTICAL WIND SHEAR (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 48 UNDER THE DOMINANT STEERING STR. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN MOSTLY UNCHANGED OVER THE NEXT 12 HOURS, ALLOWING STY NANGKA TO MAINTAIN ITS CURRENT INTENSITY. BEYOND TAU 12, ENVIRONMENTAL CONDITIONS WILL BEGIN TO DETERIORATE AS STY NANGKA MOVES INTO A MODERATE TO HIGH VWS ENVIRONMENT AND REDUCED POLEWARD OUTFLOW. NEAR TAU 48, 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 IS IN EXCELLENT AGREEMENT THROUGH TAU 72 AND REMAINS IN DECENT AGREEMENT BEYOND TAU 72. HOWEVER, NAVGEM AND COAMPS-TC REMAIN AN OUTLIER, RECURVING THE SYSTEM INTO THE MID- LATITUDE WESTERLIES. DUE TO THE CONTINUED SPREAD IN THE MODEL SOLUTIONS AFTER 72 HOURS BECAUSE OF THEIR DEPICTION OF THE APPROACHING MID-LATITUDE TROUGH, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.// NNNN