MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DUJUAN) WARNING NR 13// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (DUJUAN), LOCATED APPROXIMATELY 517 NM SOUTH-SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH TIGHTLY-CURVED BANDING WRAPPING INTO AN ELONGATED BUT DEFINED CENTER. A 241622Z GCOM 37GHZ IMAGE SHOWS MULTIPLE CONVECTIVE BANDS WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER WITH A DEFINED MICROWAVE EYE FEATURE, THEREFORE, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT TRACK MOTION. ANIMATED WATER VAPOR IMAGERY REVEALS SIGNIFICANTLY IMPROVED OUTFLOW, ESPECIALLY OVER THE EASTERN SEMI-CIRCLE, DUE TO DECREASED VERTICAL WIND SHEAR. THE INITIAL INTENSITY IS ASSESSED AT 55 KNOTS, HEDGED HIGHER THAN THE DVORAK ESTIMATES OF T3.0 (45 KNOTS) BASED ON THE CONVECTIVE STRUCTURE. TS DUJUAN IS TRACKING SLOWLY ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR) WITHIN A WEAK STEERING ENVIRONMENT. 3. FORECAST REASONING. A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. RECENT 500MB ANALYSES DEPICT A SHORTWAVE TROUGH OVER WESTERN JAPAN WITH A BREAK IN THE STR NEAR OKINAWA. THE ANALYSES ALSO INDICATE THAT THE WESTERN STR IS BUILDING INTO THE EAST CHINA SEA AS THE SHORTWAVE TROUGH PROPAGATES EASTWARD OVER THE EASTERN STR. FURTHERMORE, THE UPPER-LEVEL FLOW OVER ASIA IS ZONAL, WHICH SHOULD ALLOW THE STR TO CONTINUE TO BUILD NORTH OF THE SYSTEM, RE- ESTABLISHING THE DOMINANT STEERING INFLUENCE. TS 12W SHOULD CONTINUE TRACKING NORTHWESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 72. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT WITH SOME DIFFERENCES IN TRACK SPEED AND TIMING OF THE WESTWARD TURN, HOWEVER, GUIDANCE (INCLUDING ENSEMBLE GUIDANCE) HAS IMPROVED SIGNIFICANTLY AND HAS REMAINED CONSISTENT OVER THE PAST DAY. AFTER TAU 24, TS 21W IS FORECAST TO RAPIDLY INTENSIFY AFTER TAU 12 TO A PEAK INTENSITY OF 115 KNOTS BY TAU 72. C. IN THE EXTENDED TAUS, TS 21W WILL TURN WESTWARD AS IT BEGINS TO TRACK UNDER THE STEERING INFLUENCE OF THE WESTERN STR. DYNAMIC GUIDANCE HAS IMPROVED WITH THE MAJORITY OF MODELS NOW SHOWING A WESTWARD TRACK NEAR TAIWAN, HOWEVER, THERE IS UNCERTAINTY IN THE EXACT LANDFALL POINT WITH SOLUTIONS RANGING FROM CENTRAL TAIWAN TO NEAR 28N. TS 21W IS EXPECTED TO WEAKEN AS IT APPROACHES TAIWAN DUE TO LAND INTERACTION AND WILL BEGIN DISSIPATING RAPIDLY AS IT TRACKS INTO CHINA. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK DUE TO TRACK UNCERTAINTY, MAINLY AFTER TAU 72.// NNNN NNNN