MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (YUTU) WARNING NR 04// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 31W (YUTU), LOCATED APPROXIMATELY 638 NM EAST-SOUTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS DEEP CONVECTION AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC) ALONG WITH AN EXPANDING CLOUD FIELD. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE AND IS BASED ON A 220544Z HMS 89GHZ MICROWAVE IMAGE WHICH SHOWS THE DEEPEST CONVECTION IS LOCATED TO THE EAST AND THE SOUTH OF THE LLCC. THE INITIAL INTENSITY OF 40 KNOTS IS HEDGED BETWEEN DVORAK INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW, KNES, AND RJTD AND A 220542Z SATCON ESTIMATE OF 44 KNOTS AND AN ADT ESTIMATE OF T2.9 (43 KNOTS). ENVIRONMENTAL ANALYSIS SHOWS THAT TS 31W IS EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (5 TO 10 KNOTS) AND HAS EXCELLENT RADIAL OUTFLOW. SEA SURFACE TEMPERATURES REMAIN WARM (30 TO 32 DEGREES CELSIUS) AND WILL ALLOW FOR CONTINUED DEVELOPMENT. TS 31W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, TS 31W WILL CONTINUE TRACKING TOWARD THE NORTHWEST AROUND THE AFOREMENTIONED STR, WITH ENVIRONMENTAL CONDITIONS REMAINING FAVORABLE FOR INTENSIFICATION. MODEL GUIDANCE IS INDICATING RAPID INTENSIFICATION WHICH SEEMS LIKELY BASED ON FAVORABLE VERTICAL WIND SHEAR AND SEA SURFACE TEMPERATURES ALONG WITH EXCELLENT RADIAL OUTFLOW. BY TAU 24, TS 31W WILL REACH AN INTENSITY OF 70 KNOTS. ADDITIONAL INTENSIFICATION TO 110 KNOTS WILL OCCUR BY TAU 72. DYNAMIC MODEL GUIDANCE CONTINUES TO SHOW A NORTHWESTWARD TRACK THROUGH TAU 72. ADDITIONALLY, MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH A SMALLER SPREAD THROUGH TAU 72. THEREFORE, THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. BEYOND TAU 72, A WEAKNESS IN THE STR INDUCED BY AN UPPER-TROPOSPHERIC TROUGH WILL ALLOW FOR A SLIGHTLY MORE NORTHWARD TRACK. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE FOR CONTINUED INTENSIFICATION WITH LOW VERTICAL WIND SHEAR AND HIGH OCEAN HEAT CONTENT. DYNAMIC MODEL GUIDANCE REMAINS IN POOR AGREEMENT BEYOND TAU 72. AFUM AND ECMWF INDICATE A MORE WESTWARD TRACK WHILE GFS AND NAVGEM INDICATE A CONTINUED NORTHWESTWARD TRACK. THE GFS AND ECMWF ENSEMBLE TRACKERS ARE AT THE EDGES OF THE MODEL ENVELOPE WITH A SPREAD OF 540NM BETWEEN THEM BY TAU 120. THE GFS ENSEMBLE FAVORS A NORTHWARD TRACK WHILE THE ECMWF ENSEMBLE FAVORS A WESTWARD TRACK. DUE TO THE WIDE SPREAD IN MODEL GUIDANCE BY TAU 120 THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN