WDPN31 PGTW 231500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DUJUAN) WARNING NR 08// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (DUJUAN), LOCATED APPROXIMATELY 623 NM SOUTHEAST OF KADENA AB, JAPAN HAS TRACKED WESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY CONTINUES TO SHOW A BROAD AND ELONGATED CIRCULATION WITH AN AREA OF DEEP CONVECTION ALONG THE WESTERN PERIPHERY. A 231151Z METOP- A MICROWAVE INAGE FURTHER DEPICTS THE ELONGATED SHALLOW BANDING FORMING THE LOW LEVEL CIRCULATION CENTER (LLCC). HOWEVER, A 231150Z ASCAT BULLSEYE PROVIDES GOOD CONFIDENCE IN THE INITIAL POSITION AND SUPPORTS THE INCREASE IN CURRENT INTENSITY TO 45 KNOTS. IN ADDITION, THIS IMAGE WAS USED TO ADJUST THE CURRENT AND FORECASTED WIND RADII. UPPER LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH 20 TO 25 KNOT EASTERLY VERTICAL WIND SHEAR (VWS) KEEPING THE CONVECTION OFFSET FROM THE LLCC. GOOD DIVERGENT OUTFLOW IS SUSTAINING THE CURRENT CONVECTION. TS DUJUAN IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 21W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD OVER THE NEXT 24 HOURS AS THE STR REMAINS NORTH OF THE SYSTEM. CONCURRENTLY, EXPECT MARGINAL INTENSIFICATION DUE TO MODERATE VWS CONTINUING TO PREVENT THE SYSTEM FROM FULLY CONSOLIDATING. BEYOND TAU 24, A SHORTWAVE MID-LATITUDE TROUGH WILL CREATE A SMALL BREAK IN THE STR, ALLOWING TS 21W TO TURN MORE NORTHWESTWARD. DECREASED VWS AND IMPROVED DIVERGENT OUTFLOW WILL INCREASE THE RATE OF INTENSIFICATION. C. IN THE EXTENDED TAUS, TS 21W WILL CONTINUE TO TRACK TOWARDS THE WEAK BREAK IN THE STEERING STR AND MAINTAIN INTENSIFY AS VWS INCREASES ONCE AGAIN AND OUTFLOW IS HAMPERED. DYNAMIC MODEL GUIDANCE CONTINUES TO SHOW A TRIFURCATION. NAVGEM AND THE EUROPEAN MODELS SHOW A WEAKER SYSTEM PASSING THROUGH THE SOUTHERN RYUKYU ISLANDS. ENVIRONMENTAL CONDITIONS WILL SUPPORT AN INTENSIFICATION MAKING THESE SOLUTIONS LESS REALISTIC. HWRF, COAMPS-TC, AND THE JAPANESE MODELS SHOW A SHARP RECURVE BEFORE THE SYSTEM REACHES THE RYUKYU ISLANDS. TS DUJUAN IS NOT FORECASTED TO BE STRONG ENOUGH IN THE NEAR TERM TO BREAK THROUGH THE STEERING STR AND RECURVE NORTH. GFS, GFS ENSEMBLE MEAN, AND GFDN SHOW A STRAIGHT NORTHWESTWARD TRACK PASSING OVER OKINAWA WITH THE POSSIBILITY OF A LATER RECURVE. THIS SOLUTION IS DEEMED MOST FEASIBLE AT THIS TIME BASED ON THE EXPECTED DEVELOPMENT OF THE SYSTEM AND SUPPORTS THE CURRENT FORECAST TRACK. THE AVAILABLE ENSEMBLE CLUSTERS ALSO CONTINUE TO SHOW ALL THREE SOLUTIONS AS A POSSIBILITY LEADING TO FURTHER UNCERTAINTY. DUE TO THE CONTINUED WIDE SPREAD AND INSTABILITY IN ALL MODEL GUIDANCE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.// NNNN