WDPN31 PGTW 160300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 15W (CHOI-WAN)/ WARNING NR 17// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. SUPER TYPHOON (STY) 15W (CHOI-WAN), LOCATED APPROXIMATELY 250 NM NORTH-NORTHWEST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 09 KNOTS OVER THE LAST 06 HOURS. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS AN IMPRESSIVE SYSTEM WITH DEEP CONVECTIVE BANDING WRAPPING INTO A CENTER WITH A WELL DEFINED EYE. INTENSITY IS BASED ON ESTIMATES FROM PGTW, KNES AND RJTD. STY 15W HAS TRACKED ALONG THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL SUBTROPICAL RIDGE (STR) THAT EXTENDS FROM NORTHEAST OF STY 15W INTO THE VICINITY OF IWO TO. TRACK SPEEDS HAVE REMAINED FAIRLY CONSISTENT OVER THE PAST 12 HOURS, RANGING FROM 08 TO 10 KNOTS. AN TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) TO THE NORTHEAST HAS CONTINUED TO PROVIDE GOOD EASTWARD OUTFLOW, IN ADDITION TO AN UPPER LEVEL POINT SOURCE ANTICYCLONE OVER STY 15W THAT HAS BEEN PROVIDING STRONG RADIAL OUTFLOW OVER THE PAST 24 HOURS. THE MULTIPLE OUTFLOW MECHANISMS IN CONCERT WITH HIGH VALUES OF OCEAN HEAT CONTENT (OHC) AND SEA SURFACE TEMPERATURES (SST) HAVE ALLOWED FOR STY 15W TO INTENSIFY FURTHER OVER THE PAST 12 HOURS. 3. FORECAST REASONING. A. THE FORECAST PHILOSOPHY HAS CHANGED SLIGHTLY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE, WITH TRACK SPEED INCREASING AFTER THE SYSTEM RECURVES TO THE NORTHEAST AS THE GRADIENT BETWEEN THE STR AND AN APPROACHING MID-LATITUDE TROUGH IS FORECASTED TO BE GREATER THAN PREVIOUSLY THOUGHT. B. STY CHOI-WAN WILL BEGIN TO SLOWLY TRACK MORE NORTHWESTWARD THROUGH TAU 48 UNDER THE INFLUENCE OF THE STR DESCRIBED IN PARA 2.A. THE SYSTEM WILL SLOWLY INTENSIFY OVER THE NEXT 12 TO 24 HOURS AND THEN MAINTAIN THE SUPER TYPHOON INTENSITY THROUGH TAU 48 WITH MULTIPLE UPPER LEVEL OUTFLOW CHANNELS SUPPORTING THE STRONG INFLOW OVER REGIONS OF HIGH OHC AND SST VALUES. BY TAU 36, STY 15W WILL REACH THE WESTERN EXTENT OF THE STR AND BEGIN TO TRACK MORE NORTHWARD AROUND THE RIDGE AXIS. BY TAU 48 STY 15W WILL BEGIN TO RECURVE NORTHEASTWARD. C. BEYOND TAU 72, CHOI-WAN WILL MAINTAIN A NORTHEASTWARD TRACK AHEAD OF AN APPROACHING MID-LATITUDE TROUGH, WITH A STEADY INCREASE IN TRACK SPEED THROUGH TAU 120. THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION AROUND TAU 96 AS IT INTERACTS WITH THE APPROACHING MID- LATITUDE TROUGH. THE NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH A MODERATE TRACK SPREAD DURING THE RECURVATURE, WITH EGRR AS THE WESTERN OUTLIER (REACHING WESTERN EXTENT AT 137E) AND THE MAIN GROUPING OF MODELS REACHING 140E. THE MODELS ARE IN GOOD AGREEMENT FOR TRACK AFTER TAU 48 ALONG THE NORTHWESTERN EXTENT OF THE STR. THERE IS A LARGE MODEL SPREAD WITH REGARDS TO ALONG-TRACK SPEED AFTER RECURVATURE WITH THIS FORECAST FOLLOWING CLOSE TO CONSENSUS.// NNNN