MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (YUTU) WARNING NR 20// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON 31W (YUTU), LOCATED APPROXIMATELY 391 NM WEST- NORTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS STY 31W HAS MAINTAINED A STRONG, SYMMETRIC CONVECTIVE EYEWALL AND WELL- DEFINED EYE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE 22NM-WIDE EYE IN ENHANCED INFRARED SATELLITE IMAGERY. HOWEVER, RECENT ANIMATED SATELLITE IMAGERY CONTINUES TO INDICATE TROCHOIDAL TRACK MOTION. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH LOW (10 TO 15 KNOTS) EASTERLY VERTICAL WIND SHEAR AND ROBUST OUTFLOW WITH THE EXCEPTION OF THE EASTERN QUADRANT, WHERE AN UPPER LEVEL ANTICYCLONE TO THE EAST IS IMPINGING ON UPPER LEVEL OUTFLOW. THE INITIAL INTENSITY IS HELD AT SUPER TYPHOON STRENGTH (130 KTS) BASED ON THE PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES OF T6.5 (127 KTS), UNDER THE 260332Z SATCON ESTIMATE OF 140 KTS, BUT CONSISTENT WITH THE AUTOMATED DVORAK TECHNIQUE ESTIMATE OF 132 KTS. STY 31W IS TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHWEST PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. THERE IS A BREAK IN THE STR TO THE NORTHWEST OF THE SYSTEM ASSOCIATED WITH A WEAK MIDLATITUDE SHORTWAVE TROUGH MOVING INTO THE YELLOW SEA. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. WIND RADII WERE ADJUSTED BASED ON A 260034Z ASCAT IMAGE. B. STY 31W IS FORECAST TO CONTINUE TRACKING WEST-NORTHWESTWARD TOWARD THE BREAK IN THE STR THROUGH TAU 36, HOWEVER, THE SYSTEM SHOULD GRADUALLY TURN MORE WESTWARD AFTER TAU 36 AS THE AFOREMENTIONED SHORTWAVE TROUGH PROPAGATES EASTWARD AND A BROAD MIDLATITUDE RIDGE TO THE NORTH ALLOWS THE STR TO RE-BUILD. EXCLUDING THE PRIMARY OUTLIERS, COAMPS-TC (CTCX) AND NAVGEM, DYNAMIC MODEL GUIDANCE IS IN BETTER AGREEMENT THROUGH TAU 72 WITH A 140NM SPREAD IN SOLUTIONS AT TAU 72. STY 31W IS EXPECTED TO MAINTAIN NEAR-STY STRENGTH THROUGH TAU 12 AS THE EYEWALL RE-STRENGTHENS AND THE EYE CONTRACTS. HOWEVER, AFTER TAU 12, THE SYSTEM SHOULD GRADUALLY WEAKEN AS VERTICAL WIND SHEAR INCREASES TO MODERATE LEVELS. C. BEYOND TAU 72, THERE IS INCREASING UNCERTAINTY IN THE FORECAST TRACK WITH TWO DISTINCT CLUSTERS OF MODEL GUIDANCE. ECMWF, EEMN, UKMET, JGSM, AFUM, GFS, AEMN AND HWRF INDICATE A WEST-SOUTHWESTWARD (OVER LUZON) TO WEST-NORTHWESTWARD (TOWARD THE LUZON STRAIT) TRACK. NAVGEM, COAMPS-NAVGEM, AND COAMPS-GFS CONTINUE TO INDICATE AN UNLIKELY RECURVE SCENARIO. THOUGH THE MIDLATITUDE TROUGH WILL CREATE A BREAK IN THE STR, THE TROUGH WILL BE ASSOCIATED WITH A COLD NORTHEASTERLY SURFACE SURGE THAT WILL PREVENT THE SYSTEM FROM RECURVING SIGNIFICANTLY NORTH. THE JTWC FORECAST TRACK FAVORS A MORE WESTWARD TRACK WITH A DECREASE IN TRACK SPEEDS ASSOCIATED WITH A BREAK IN THE STR AND THE SURFACE COLD SURGE. STY 31W WILL CONTINUE TO GRADUALLY WEAKEN UNDER INCREASING VERTICAL WIND SHEAR AND THE COLD, DRY AIR ASSOCIATED WITH THE NORTHEASTERLY COLD SURGE, ALTHOUGH SSTS REMAIN FAVORABLE INTO THE LUZON STRAIT, BETWEEN 26-27 DEGREES CELSIUS. BASED ON THE BIFURCATION IN THE DYNAMIC MODELS AND LARGE OVERALL SPREAD, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN