MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR 36// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 15W (TEMBIN), LOCATED APPROXIMATELY 195 NM SOUTH OF TAIPEI, TAIWAN, HAS TRACKED EAST-NORTHEASTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS DEEP CONVECTION IS LIMITED TO THE SOUTHWESTERN QUADRANT OF THE LOW LEVEL CIRCULATION CENTER (LLCC). RADAR IMAGERY FROM TAIWAN DEPICTS A WELL ORGANIZED LLCC BUT WITH DIMINISHED CONVECTION ALONG THE NORTHEASTERN QUADRANT AS THE SYSTEM IS TRACKING NEAR THE COAST OF TAIWAN. ADDITIONALLY, THERE APPEARS TO BE SOME ELONGATION AND EXPANSION OF THE LLCC OVER THE PAST FEW HOURS. THE CURRENT INTENSITY OF 55 KNOTS IS BASED ON A 3.5/3.5 DVORAK FROM PGTW, AND IS CONSISTENT WITH THE RECENT WEAKENING OBSERVED. UPPER LEVEL ANALYSIS INDICATES TS 15W IS LOCATED TO THE SOUTHWEST OF AN ANTICYCLONE LOCATED OVER OKINAWA. UPPER LEVEL RIDGING EXTENDING FROM THE ANTICYCLONE OVER TAIWAN IS CREATING MODERATE LEVELS OF NORTHEASTERN VERTICAL WIND SHEAR (VWS) AND IS CAUSING THE DISLOCATION OF CONVECTION WITHIN THE NORTHEASTERN QUADRANT. THERE IS HIGH CONFIDENCE IN THE POSITION BASED ON AVAILABLE RADAR DATA. TS 15W IS TRACKING ALONG THE NORTHERN PERIPHERY OF A DEVELOPING NEAR EQUATORIAL RIDGE (NER). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 15W IS FORECAST TO REMAIN ON A NORTHEASTWARD TRACK FOR THE NEXT 12 HOURS, TRANSITIONING TO A GENERAL NORTHWARD TRACK BEYOND TAU 12 THROUGH TAU 72 AS A BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST BECOMES THE DOMINANT STEERING INFLUENCE. THE INTENSITY IS EXPECTED TO DECREASE OVER THE NEXT 24 HOURS AS IMPACTS FROM THE PROXIMITY TO TAIWAN DISRUPTS LOW LEVEL INFLOW. BETWEEN TAU 24 AND 72 A SLIGHT INTENSITIFICATION PERIOD IS EXPECTED AS THE SYSTEM REORGANIZES IN A FAVORABLE SURFACE ENVIRONMENT. THE UPPER LEVEL WILL REMAIN MARGINAL WHICH WILL LIMIT STRONGER INTENSIFICATION THROUGH TAU 48 WITH THE OVERALL ENVIRONMENT BECOMING LESS FAVORABLE BETWEEN TAU 48 AND 72 AS SEA SURFACE TEMPERATURES (SSTS) DECREASE AND VWS INCREASES. MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST THROUGH TAU 48, BUT BEGINS TO SEPARATE SIGNIFICANTLY BY TAU 72. THERE IS HIGH CONFIDENCE IN THE TRACK THROUGH TAU 48, BUT BECOMES LOW CONFIDENCE BY TAU 72. C. DYNAMIC MODEL GUIDANCE HAS SHIFTED OVER THE PAST SIX HOURS FOR THE EXTENDED FORECAST, WITH THE MAJORITY OF AVAILABLE GUIDANCE INDICATING A TRACK OVER THE KOREAN PENINSULA. THE CURRENT FORECAST HAS SHIFTED SLIGHTLY EASTWARD IN THE EXTENDED TAUS, BUT REMAINS ALONG THE WESTERN ENVELOP OF AVAILABLE GUIDANCE. THERE EXISTS SIGNIFICANT UNCERTAINTY WITHIN THE MODEL FIELDS REGARDING THE DEVELOPMENT OF THE DEEP LAYERED STR THAT IS EXPECTED TO STEER TS 15W AS TY 16W (BOLAVEN) MOVES INTO THE MID-LATITUDE FLOW. THE INTENSITY IS EXPECTED TO CONTINUE WEAKENING AS THE SSTS DECREASE AND VWS INCREASES. EXTRA-TROPICAL TRANSITION IS EXPECTED TO BEGIN BY TAU 96 WITH COMPLETE TRANSITION BY TAU 120. BASED ON THE COMPLEX STEERING PATTERN AND THE ERRATIC NATURE OF HALF THE DYNAMIC MODELS, THERE IS LOW CONFIDENCE IN THE EXTENDED FORECAST TRACK.// NNNN NNNN