WDPN31 PGTW 240900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SURIGAE) WARNING NR 44// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUBTROPICAL STORM (SS) 02W (SURIGAE), LOCATED APPROXIMATELY 531 NM WEST-SOUTHWEST OF IWO TO, HAS TRACKED EAST-SOUTHEASTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD, FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH DISORGANIZED CONVECTION FIRING IN THE UNSTABLE EAST AND NORTHEAST QUADRANTS. THE EXPOSED LLCC AND A 240439Z AMSR2 37GHZ MICROWAVE IMAGERY REVEALED THE LOW LEVEL STRUCTURE OF THE BROAD CIRCULATION TO GOOD EFFECT AND LENT HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS HEDGED ABOVE THE MULTI- AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T2.5 (35 KTS) BASED ON A SERIES OF SCATTEROMETER PASSES BETWEEN 240009Z TO 240219Z AS WELL AS AN AMSR2 WINDSPEED ESTIMATE AT 240439Z, ALL OF WHICH INDICATES MAXIMUM WINDS OF 45 KTS TO THE NORTHWEST AND NORTHEAST OF THE LLCC. ENVIRONMENTAL ANALYSIS REVEALS 02W IS EMBEDDED WITHIN THE SUBTROPICAL WESTERLIES UNDER APPROXIMATELY 30-40 KNOTS OF WESTERLY VERTICAL WIND SHEAR AND IS TRACKING OVER COOLER SST (24-25C). THE SYSTEM IS ALSO ENTRAINING A DRY AIR MASS, PARTICULARLY IN THE SOUTHWESTERN QUADRANT, AS EVIDENCED BY THE LACK OF ANY SIGNIFICANT CONVECTIVE CLOUDS IN THIS QUADRANT. REGIONAL UPPER-AIR ANALYSIS INDICATES ONE SHORTWAVE TROUGH EXITING THE REGION TO THE NORTHEAST, WHILE ANOTHER, MUCH STRONGER MAJOR SHORTWAVE TROUGH, CURRENTLY ENTERING THE FAR NORTHERN EAST CHINA SEA, IS RAPIDLY DIVING SOUTHWARDS TOWARDS SURIGAE. THIS NEXT SHORTWAVE WILL BE THE ULTIMATE TRIGGER FOR EXTRA-TROPICAL TRANSITION. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. OVER THE NEXT 36 HOURS, SS 02W IS FORECAST TO BEGIN ACCELERATING TO THE EAST THEN NORTHEAST, TO THE SOUTH OF IWO TO, AS IT COMES UNDER THE STEERING INFLUENCE OF THE STRONG MID-LATITUDE WESTERLY FLOW. AS THE AFOREMENTIONED MAJOR SHORTWAVE TROUGH DIVES SOUTHWARD THROUGH THE NEXT 24 HOURS, IT WILL INDUCING SIGNIFICANT BAROCLINIC FORCING AND THERMAL ADVECTION, AND ULTIMATELY BRING ABOUT TRANSITION TO A STRONG GALE-FORCE EXTRATROPICAL SYSTEM BY TAU 36. THE JTWC FORECAST TRACK REMAINS CONSISTENT WITH THE PREVIOUS ONE. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH THE DURATION OF THE FORECAST PERIOD WITH INCREASING ALONG-TRACK SPREAD AFTER TAU 24 AS THE SYSTEM COMPLETES EXTRATROPICAL TRANSITION. OVERALL CONFIDENCE IN THE JTWC FORECAST REMAINS HIGH.// NNNN