MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (SAOLA) WARNING NR 27// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 27W (SAOLA), LOCATED APPROXIMATELY 533 NM SOUTH- SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A 260414Z 89GHZ AMSR2 IMAGE SHOWS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH BANDING CONVECTION WRAPPING IN FROM THE WEST AND SOUTHERN PERIPHERIES, AND IS THE BASIS FOR THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 45 KNOTS WHICH IS BASED ON AGENCY DVORAK ESTIMATES OF T3.0 (45 KNOTS), A PREVIOUS 260001Z OSCAT IMAGE SHOWING 40 KNOTS ON THE SOUTHWESTERN QUADRANT, AND A 260416Z SATCON ESTIMATE OF 51 KNOTS. UPPER-LEVEL ANALYSIS SHOWS AN ANTICYCLONE JUST NORTHEAST OF TS 27W CREATING STRONG EASTERLY CONDITIONS, WITH A WELL ESTABLISHED RIDGE PROTRUDING WESTWARD LIMITING THE POLEWARD OUTFLOW CHANNEL. DESPITE THE PREVALENT EASTERLIES TS 27W IS STRUGGLING TO CREATE A POINT SOURCE OVER THE LLCC, EVIDENCED BY WEAK ANTICYCLONIC ROTATION AND RELATIVELY LOW VERTICAL WIND SHEAR. SSTS IN THE REGION ARE ALSO NOT IMPRESSIVE AT 27 TO 28 CELSIUS, BUT ARE STILL RELATIVELY WARM TO FUEL CYCLOGENESIS. CURRENTLY TS 27W IS TRACKING TO THE NORTHWEST ALONG THE SOUTHWESTERN EXTENT OF A MID-TO-LOW LEVEL SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE, HOWEVER THE FORECAST TRACK HAS SHIFTED WESTWARD NOW MAKING LANDFALL OVER OKINAWA NEAR TAU 48. B. TS 27W IS FORECAST TO CONTINUE ON ITS NORTHWESTWARD TRACK OVER THE NEXT 36 TO 48 HOURS GUIDED BY THE EASTERN EDGE OF THE STR. THE UPPER-LEVEL RIDGE IS FORECAST TO WEAKEN GRADUALLY OVER THE NEXT 12 TO 48 HOURS IMPROVING OUTFLOW CONDITIONS AND TS 27W IS EXPECTED TO GRADUALLY INTENSIFY. JUST BEFORE TAU 48 A SHORTWAVE TROUGH WILL MOVE INTO THE REGION FURTHER WEAKENING THE RIDGE AND ENHANCING THE POLEWARD OUTFLOW CHANNEL LEADING TO A FASTER RATE OF INTENSIFICATION, REACHING A PEAK INTENSITY OF 75 KNOTS, AND A SHIFT IN TRACK MOTION TO THE NORTH EAST AS IT ROUNDS THE RIDGE AXIS. DYNAMIC MODEL GUIDANCE SHOWS DIVERGENCE IN THE SHORT-TERM TRACK RELATED TO THE STRENGTH OF THE MID-LEVEL SHORTLY BEFORE AND DURING THE TROUGH PASSAGE. THE GFS SOLUTION HAS PROVEN TO BE THE MOST CONSISTENT OVER THE LAST SEVERAL DAYS AS THE FAR WESTERN OUTLIER WITH NAVGEM AND ECMWF ONLY RECENTLY FAVORING A WESTWARD TRACK. THE FORECAST TRACK IS NOW BIASED TOWARD THESE SOLUTIONS WITH A TRACK DIRECTLY OVER THE ISLAND OF OKINAWA. C. IN THE EXTENDED FORECAST, TS 27W WILL ACCELERATE EAST- NORTHEASTWARD JUST AFTER TAU NEAR TAU 60 ONCE CAPTURED BY THE MID- LEVEL TROUGH. THIS WILL COINCIDE WITH A COLD SURGE EVENT OVER THE SEA OF JAPAN AND EAST CHINA SEA ENHANCING THE GALE FORCE WIND DISTRIBUTION. TS 27W WILL BEGIN TRANSITIONING INTO COLD CORE LOW AROUND TAU 72 AS THE COOL DRY AIR AND BAROCLINIC INSTABILITY RAPIDLY DETERIORATE THE SYSTEM. THE UPPER-LEVEL JET IS FORECAST TO STRENGTHEN AND REMAIN FAIRLY ZONAL OVER THE SOUTHERN PORTION OF THE JAPANESE ISLANDS, INCREASING VERTICAL WIND SHEAR AND KEEPING THE TRACK FURTHER SOUTH. DYNAMIC MODELS DIVERGE SIGNIFICANTLY AFTER TAU 72 WITH GFS AND NOW ECMWF SHOWING TRACK SOUTH OF 30 DEGREES NORTH, AND MOST OTHERS SKIRTING THE SOUTHERN COASTLINE OF HONSHU. NAVGEM KEEPS THE SYSTEM QUASI-STATIONARY JUST AFTER TAU 48 DUE TO AN UNREALISTIC STRENGTHENING MID-LEVEL RIDGE WHILE THE TROUGH MOVES THROUGH. BECAUSE OF THE UNCERTAINTY IN AVAILABLE GUIDANCE, THERE IS STILL LOW CONFIDENCE IN THE FORECAST TRACK. GIVEN THE RECENT CONSISTENCY IN THE GFS SOLUTION, PERFORMANCE RECORD WITH ECMWF, AND AGREEMENT BETWEEN THE TWO, THE JTWC FORECAST TRACK HEDGED TOWARD THESE SOLUTIONS.// NNNN NNNN