WDPN31 PGTW 230300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 17// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 185 NM SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL AND ENHANCED INFRARED SATELLITE IMAGERY SHOWED A BRIEF PERIOD WHEN THE EYE WAS CLEARED BUT SINCE THEN HAS BECOME MORE CLOUD OBSCURED. A 230006Z SSMIS 91 GHZ MICROWAVE IMAGE REVEALS A NEARLY UNIFORM CONCENTRIC DEEP EYEWALL STRUCTURE THAT IS SLIGHTLY FRAGMENTED OVER THE SOUTHWESTERN QUADRANT. THE CURRENT POSITION IS BASED ON RADAR FIXES FROM JAPAN AND TAIWAN, ALONG WITH THE SSMIS IMAGE, WITH HIGH CONFIDENCE. THE CURRENT INTENSITY IS BASED ON THE HIGHER SIDE OF DVORAK INTENSITY ESTIMATES, RANGING FROM 77 TO 102 KNOTS FROM RJTD AND PGTW/KNES RESPECTIVELY, DUE TO THE VIGOROUS EYEWALL STRUCTURE. TRACK SPEEDS CONTINUE TO BE SLOW AS THE PRIMARY STEERING INFLUENCE, A DEEP LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH, HAS BEEN WEAKENED BY A TRANSITING MID-LATITUDE TROUGH EXITING THE KOREAN PENINSULA. UPPER- LEVEL ANALYSIS INDICATES THE POLEWARD OUTFLOW TOWARDS THE TROPICAL UPPER-TROPOSPHERIC TROUGH CELL THAT WAS LOCATED OVER SOUTHERN HONSHU HAS BEEN SHUT DOWN AS THE CELL FILLED INTO TROUGHING. CURRENTLY THERE IS VERY WEAK POLEWARD OUTFLOW INTO THE UPPER-LEVEL TROUGHING BUT EQUATORWARD OUTFLOW REMAINS ROBUST. THE SELF-INDUCED MESO- ANTICYCLONE IS STILL IN PLACE OVER THE LLCC PROVIDING FOR MODERATE DIVERGENCE ALOFT AND WEAK (05-10 KNOTS) VERTICAL WIND SHEAR (VWS). SEA SURFACE TEMPERATURES WITHIN THE REGION REMAIN FAVORABLE (28 TO 30 CELSIUS) ALONG THE FORECAST TRACK. TY 15W IS CURRENTLY BEING STEERED WESTWARD BY A WEAK EXTENSION OF THE STR, AS INDICATED BY THE 35 KNOT 500 MB EASTERLIES IN THE 230000Z RADIOSONDE FROM ISHIGAKI- JIMA (24.33N 124.16E). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 15W WILL CONTINUE TO STEER WESTWARD INTO TAIWAN VIA THE WEAK EXTENSION OF THE STR. FURTHER INTENSIFICATION IS EXPECTED DUE TO CONTINUED FAVORABLE ENVIRONMENTALS MENTIONED EARLIER. BY TAU 24 TY 15W SHOULD MAKE LANDFALL WHERE THE LLCC WILL BEGIN TO SLIGHTLY WEAKEN DUE TO LAND INTERACTION AND LACK OF OCEAN HEAT. HOWEVER, TY 15W IS EXPECTED TO EMERGE OFF THE WESTERN COAST OF TAIWAN AFTER ONLY BEING OVERLAND FOR APPROXIMATELY 12 HOURS. THE SYSTEM WILL THEN SLOWLY DRIFT WEST-SOUTHWESTWARD IN A WEAK STEERING ENVIRONMENT WITH A BUILDING NEAR EQUATORIAL RIDGE TO THE SOUTHEAST AND A DEEPLY DIGGING TROUGH OVER EASTERN CHINA. SLOW INTENSIFICATION IS EXPECTED DURING THIS TIME DUE TO A POCKET OF WARM OCEAN HEAT CONTENT, WARM SEA SURFACE TEMPERATURES, AND INCREASING POLEWARD OUTFLOW OUT AHEAD OF ANOTHER DIGGING TROUGH. THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST UP TO THE LANDFALL POSITION AND INTO THE TAIWAN STRAIT, BUT BY TAU 48 FORECAST CONFIDENCE DEGRADES DUE TO THE COMPLEX TIMING OF THE SYNOPTIC FEATURES. C. IN THE EXTENDED FORECAST TY 15W IS EXPECTED TO CONTINUE A SLOW DRIFT SOUTH AND THEN EVENTUALLY BACK EAST IN A COUNTERCLOCKWISE LOOP AS THE STEERING ENVIRONMENT REMAINS WEAK. THE SYSTEM SHOULD BEGIN TO WEAKEN UNDER INCREASINGLY UNFAVORABLE CONDITIONS DUE TO STRONGER VWS FROM TY 16W'S OUTFLOW. ADDITIONALLY, SOME BINARY INTERACTION WITH THE MUCH LARGER TY 16W IS EXPECTED WHICH SHOULD FURTHER ATTRACT THE LLCC BACK EASTWARD ALONG WITH UPPER-LEVEL WEST-SOUTHWEST FLOW AT THE TIME. OBJECTIVE AID GUIDANCE CONTINUES TO COME INTO BETTER AGREEMENT TOWARDS THE LOOPING MOTION WITH THE EXCEPTION OF THE WBAR, EGRR, AND GFDN. THESE THREE TRACKERS WERE DISCOUNTED DUE TO UNREALISTIC MOTION INTO, AND BEYOND, THE TROUGHING THAT WILL DEVELOP AT THIS TIME. THERE IS LOW CONFIDENCE IN THIS PORTION OF THE TRACK FORECAST DUE TO UNCERTAINTIES IN THE TIMING OF SYNOPTIC FEATURES AND COMPLEX LOOPING MOTION.// NNNN