WDPN32 PGTW 161500 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SONGA) WARNING NR 08// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM (TS) 19W (SONCA), LOCATED APPROXIMATELY 500 NM EAST OF IWO TO, JAPAN, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A 161151Z SSMI IMAGE CONFIRM THAT VIGOROUS CONVECTION IS PERSISTING OVER THE CORE OF A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A 160716Z SSMIS IMAGE DEPICTS TIGHTLY-CURVED BANDING WRAPPING INTO A WELL-DEFINED LLCC, BUT IT ALSO INDICATES A SIGNIFICANT AMOUNT OF DRY AIR IS FEEDING INTO THE CENTER OF THE STORM, PARTICULARLY OVER THE WESTERN QUADRANT. ANIMATED WATER VAPOR IMAGERY SHOWS IMPINGEMENT ON OUTFLOW OVER THE WESTERN SEMICIRCLE HAS EASED SIGNIFICANTLY. A POLEWARD OUTFLOW CHANNEL OVER THE NORTHEASTERN QUADRANT IS CUTTING OFF AS A HIGH AMPLITUDE RIDGE BUILDS OVER THE 140TH MERIDIAN. VERTICAL WIND SHEAR IS NEAR 10 KNOTS AND SEA SURFACE TEMPERATURE IS 27 DEGREES. THE 160000Z PGTW UPPER LEVEL STREAMLINE ANALYSIS REVEALS A TUTT CELL IS LOCATED OVER THE LLCC, WHICH WAS SUPPRESSING CONVECTION AND RESULTING IN DVORAK ESTIMATES THAT WERE LOWER THAN ACTUAL INTENSITY. RECENT IMAGERY INDICATES THAT THE CORE CONVECTION HAS BECOME VIGOROUS ENOUGH TO OVERCOME THE SUBSIDENCE. THE MOST RECENT AMSU CROSS SECTIONS CONTINUED WARMING IN THE MID-LEVELS OF THE SYSTEM. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS 19W WILL CONTINUE TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP SUBTROPICAL STEERING RIDGE WITH GRADUAL ACCELERATION ALONG A NORTHWESTERLY COURSE THROUGH TAU 36, THEN CREST THE RIDGE AND RE- CURVE INTO THE MID-LATITUDES WELL EAST OF THE KANTO PLAIN. MODEL GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH TAU 48, THEN DIVERGES DUE TO DIFFERENCES IN TRANSLATION SPEEDS. ALL GUIDANCE, HOWEVER, IS IN GOOD AGREEMENT ON THE OVERALL SCENARIO AND THE GENERAL AREA OF RECURVATURE. THE JTWC TRACK FORECAST STAYS CLOSE TO CONSENSUS. THE TUTT CELL AND MARGINALLY FAVORABLE SEA SURFACE TEMPERATURES WILL KEEP TS 19W FROM INTENSIFYING MUCH BEYOND ITS CURRENT STATE. AS THE SYSTEM MOVES AROUND THE RIDGE AFTER TAU 48 AND BECOMES EMBEDDED WITHIN THE STRONG WESTERLY FLOW, IT WILL BEGIN EXTRA-TROPICAL TRANSITION. C. BETWEEN TAU 72 AND 96, TS 19W WILL ACCELERATE INTO THE HIGH LATITUDES WHILE UNDERGOING EXTRA-TROPICAL TRANSITION (XTT). THE ZONAL STATUS OF THE POLAR FRONT JET AT THAT TIME WILL RESULT IN A RELATIVELY SLOW XTT PROCESS. THICKNESS PROGS INDICATE THE TRANSITION TO A GALE FORCE LOW WILL COMPLETE NEAR TAU 84, JUST BEYOND THE 165TH MERIDIAN.// NNNN