MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DUJUAN) WARNING NR 10// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (DUJUAN), LOCATED APPROXIMATELY 541 NM SOUTH-SOUTHEAST OF KADENA AB, JAPAN HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTIVE BANDING OVER THE SOUTHERN SEMI- CIRCLE. OVERALL, CONVECTIVE ORGANIZATION HAS IMPROVED WITH EVIDENCE THAT VERTICAL WIND SHEAR (VWS) HAS DECREASED TO LOW TO MODERATE (10 TO 20 KNOTS) LEVELS. CONSEQUENTLY, ANIMATED WATER VAPOR IMAGERY INDICATES EXPANDING OUTFLOW OVER THE EASTERN SEMI-CIRCLE. THIS CONSOLIDATION IS EVIDENT IN A 232257Z SSMIS 91GHZ IMAGE, WHICH SHOWS TIGHTLY-CURVED SHALLOW BANDING WRAPPING INTO A DEFINED CENTER WITH CURVED DEEP BANDING FORMING OVER THE SOUTH QUADRANT. OVERALL, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION BASED ON THE SSMIS IMAGE. THE INITIAL INTENSITY IS ASSESSED AT 50 KNOTS BASED ON THE 232227Z RSCAT DATA AND THE IMPROVED CONVECTIVE STRUCTURE AS WELL AS RECENT SATCON ESTIMATES OF 50 KNOTS. TS DUJUAN IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR). 3. FORECAST REASONING. A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THE RECENT 500MB ANALYSES DEPICT A SHORTWAVE TROUGH OVER THE KOREAN PENINSULA EXTENDING SOUTHWARD INTO THE EAST CHINA SEA. DUE TO THIS TROUGH, TS 21W IS FORECAST TO TURN NORTHWESTWARD AND TRACK SLOWLY TOWARD THE WEAKNESS IN THE SUBTROPICAL RIDGE (STR) THROUGH TAU 36. THIS TROUGH IS FORECAST TO WEAKEN AND QUICKLY PROPAGATE EASTWARD, THEREFORE, THE STR SHOULD GRADUALLY RE-BUILD POLEWARD OF TS 21W AFTER TAU 36. DESPITE A PERSISTENT BREAK IN THE STR (BETWEEN THE WESTERN AND EASTERN STR), MODEL GUIDANCE GENERALLY INDICATES ZONAL WESTERLY FLOW WITH NO DYNAMIC MIDLATITUDE SHORTWAVE TROUGHS CAPABLE OF INDUCING A RE-CURVE SCENARIO. DYNAMIC GUIDANCE REMAINS UNCERTAIN, HOWEVER, THE MAJORITY OF THE GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72. TS 21W IS FORECAST TO SLOWLY CONSOLIDATE DUE TO THE BROAD NATURE OF THE LLCC AND LOW TO MODERATE VWS THROUGH TAU 24, HOWEVER, 12W SHOULD INTENSIFY AT A GREATER RATE AFTER TAU 24 AS VWS DECREASES AND POLEWARD OUTFLOW IMPROVES. 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. TS 21W SHOULD CONTINUE TO INTENSIFY UNTIL IT APPROACHES TAIWAN AT WHICH POINT IT WILL WEAKEN DUE TO LAND INTERACTION. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK DUE TO POSITIONAL AND TRACK UNCERTAINTY IN THE EARLY PHASE OF THE FORECAST.// NNNN NNNN