WDPN31 PGTW 210300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 09// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 360 NM SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED DEEP CONVECTIVE BANDING, TIGHTLY WRAPPED INTO A 10-NM EYE SURROUNDED BY A HIGHLY SYMMETRIC EYEWALL. THIS IS ALSO EVIDENT ON A 202141Z SSMI-S MICROWAVE IMAGE. THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION BASED ON THE EYE FEATURE. THE INITIAL INTENSITY IS BASED ON THE HIGH END OF DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER-LEVEL ANALYSIS INDICATES EXCELLENT RADIAL OUTFLOW WITH A STRONGER POLEWARD CHANNEL ENHANCED BY A TUTT CELL TO THE NORTHEAST. TY 15W IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED NEAR-EQUATORIAL RIDGE (NER) IN AN AREA OF LIGHT TO MODERATE (10-15 KNOT) VERTICAL WIND SHEAR (VWS). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 15W IS EXPECTED TO TRACK MORE NORTHWESTWARD AS THE STEERING MECHANISM SWITCHES TO A SUBTROPICAL RIDGE (STR) THAT IS BUILDING BEHIND A MID-LATITUDE TROUGH THAT IS CURRENTLY DIGGING EASTWARD INTO THE KOREAN PENINSULA. AFTER TAU 24, THE STR WILL HAVE SOLIDLY ASSUMED STEERING AND WILL FLATTEN THE TRACK DUE WESTWARD. DUE TO THE FAVORABLE ENVIRONMENT, THE TYPHOON WILL CONTINUE TO INTENSIFY, PEAKING AT 130 KNOTS AT TAU 36. DECREASED OUTFLOW, AS THE POLEWARD CHANNEL DIMINISHES, WILL CAUSE THE SYSTEM TO WEAKEN BEFORE IT MAKES LANDFALL INTO TAIWAN AFTER TAU 48. C. AFTER TAU 72, TYPHOON TEMBIN IS FORECAST TO MAINTAIN MINIMAL TYPHOON STRENGTH AS IT CROSSES THE TAIWAN STRAIT BUT WILL ERODE RAPIDLY DUE TO FRICTIONAL EFFECTS AFTER IT MAKES A SECOND AND FINAL LANDFALL NORTHEAST OF HONG KONG. THE NUMERICAL MODEL GUIDANCE IS IN OVERALL GOOD AGREEMENT WITH THE EXCEPTION OF EGRR WHICH UNREALISTICALLY DRIVES THE VORTEX POLEWARD INTO THE STEERING RIDGE. THE TRACK FORECAST IS ADJUSTED SLIGHTLY LEFT OF CONSENSUS TO OFFSET EGRR. THERE IS HIGH CONFIDENCE IN THE FORECAST TRACK. // NNNN