WDPN31 PGTW 311500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 25W (JEBI) WARNING NR 18// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON 25W (JEBI), LOCATED APPROXIMATELY 316 NM NORTHWEST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A COMPACT SYSTEM THAT HAS MAINTAINED ITS SIZE AND A 15 NM ROUND EYE. THE INITIAL INTENSITY IS ASSESSED AT 150 KNOTS, BETWEEN THE PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T7.5 (155 KNOTS), THE RJTD/KNES ESTIMATES OF T7.0 (140 KTS), AND A 310331Z SATCON ESTIMATE OF 142 KNOTS. AT 310600Z, 25W WAS ASSESSED TO BE UNDERGOING AN EYEWALL REPLACEMENT CYCLE, WHICH MAY AFFECT THE INTENSITY IN THE SHORT TERM. UPPER-LEVEL ANALYSIS REVEALS A VERY FAVORABLE ENVIRONMENT WITH LOW VERTICAL WIND SHEAR, RADIAL OUTFLOW ENHANCED BY TUTT CELLS TO THE EAST AND WEST, WARM SSTS (29-31 C) AND HIGH OCEAN HEAT CONTENT VALUES, THAT HAVE PERMITTED STY 25W TO RAPIDLY INTENSIFY OVER THE PAST SEVERAL DAYS. STY 25W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS WARNING. B. STY 25W WILL TURN NORTHWESTWARD IN THE NEXT 12 HOURS AS THE STR EXTENSION TO ITS NORTH RECEDES. NUMERICAL MODEL GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT THROUGH TAU 72 WITH A SPREAD OF 240 NM AT TAU 72. BASED ON THE LOW UNCERTAINTY IN THE TRACK GUIDANCE, CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST IS HIGH. UPPER-LEVEL OUTFLOW IS FORECAST TO BECOME LESS FAVORABLE WHILE 25W BEGINS TO ROUND THE RIDGE, LEADING TO A GRADUAL WEAKENING TREND. 25W IS STILL FORECAST TO MAINTAIN SUPER TYPHOON INTENSITY UNTIL TAU 36 UNDER OTHERWISE FAVORABLE LOW VWS AND WARM SSTS. DUE TO THE EYEWALL REPLACEMENT CYCLE, ADDITIONAL SHORT-TERM INTENSITY FLUCTUATIONS ARE POSSIBLE, AND THERE IS SOME UNCERTAINTY IN THE JTWC INTENSITY FORECAST THROUGH TAU 72. C. AFTER TAU 72, STY 25W WILL ACCELERATE NORTHWARD TO NORTH- NORTHEASTWARD TOWARD CENTRAL HONSHU AFTER IT ROUNDS THE STR AXIS. STY 25W WILL GRADUALLY WEAKEN AS A WARM-CORE TROPICAL SYSTEM BEFORE TAU 96 DUE TO AN INCREASINGLY UNFAVORABLE ENVIRONMENT WITH LOWER OCEAN HEAT CONTENT AND HIGHER VERTICAL WIND SHEAR. STY 25W IS EXPECTED TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 96 AS IT BEGINS TO INTERACT WITH A DEEP MIDLATITUDE SHORTWAVE TROUGH DIGGING INTO THE KOREAN PENINSULA AND WESTERN JAPAN, WHICH WILL TEMPORARILY ENHANCE OUTFLOW. STY 25W WILL RAPIDLY COMPLETE ETT AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE SHORTWAVE TROUGH AND GAINS FRONTAL CHARACTERISTICS OVER THE SEA OF JAPAN. THE SYSTEM WILL RAPIDLY WEAKEN AFTER TAU 96 DUE TO INCREASING VERTICAL WIND SHEAR, COLDER SSTS IN THE SEA OF JAPAN, AND INCREASED FRICTIONAL EFFECTS FROM JAPAN. AFTER COMPLETING ETT BY TAU 120, THE OCCLUDING EXTRA- TROPICAL LOW IS FORECAST TO MAINTAIN STORM-FORCE WINDS AND THE WIND FIELD IS FORECAST TO BECOME MORE EXPANSIVE AND ASYMMETRIC AS IT IS ACCELERATED POLEWARD BY THE TROUGH. MODELS STILL DEPICT SOME VARIATION IN TIMING AND SPEED OF THE RECURVE AFTER TAU 72. THEREFORE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN