MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 12// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 239 NM NORTHWEST OF ENEWETAK, HAS TRACKED WESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A SLOWLY CONSOLIDATING SYSTEM WITH DEEP CONVECTIVE BANDING STRUGGLING TO FORM OVER THE NORTHWESTERN QUADRANT. THIS IS EVIDENT IN A 161528Z NOAA-19 89GHZ IMAGE, WHICH SHOWS FRAGMENTED BANDING WRAPPING TIGHTLY INTO A WEAK MICROWAVE EYE FEATURE. RECENT IMAGERY HAS INDICATED STRONGER CONVECTIVE BANDING AND A MORE DEFINED CENTER; HOWEVER, THE SYSTEM APPEARS TO HAVE WEAKENED SLIGHTLY. DESPITE THE SLIGHT WEAKENING TREND, THE CURRENT INTENSITY IS HELD AT 65 KNOTS BASED ON T4.0 DVORAK INTENSITY ESTIMATES FROM ALL AGENCIES. ANIMATED WATER VAPOR IMAGERY CONTINUES TO SHOW EXCELLENT OVERALL OUTFLOW, ENHANCED BY A TUTT CELL NEAR THE DATELINE; HOWEVER, THE IMAGERY SUGGESTS UPPER- LEVEL CONVERGENCE ASSOCIATED WITH THE TUTT PRESSING DOWN OVER THE NORTHERN PERIPHERY OF THE SYSTEM. TY 17W REMAINS IN A COMPETING STEERING ENVIRONMENT BETWEEN A WEAK NEAR-EQUATORIAL RIDGE TO THE SOUTH AND THE STRONG STR TO THE NORTH. THIS STEERING INFLUENCE HAS GENRALLY PRODUCED A SLOW WESTWARD TRACK. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 17W WILL CONTINUE TRACKING SLOWLY WESTWARD THROUGH TAU 12 DUE TO THE COMPETING STEERING ENVIRONMENT. BEYOND TAU 12, THE NER WILL SHIFT TO THE EAST ALLOWING THE STR TO BECOME THE DOMINANT STEERING INFLUENCE. THEREFORE, TY 17W WILL ACCELERATE NORTHWESTWARD ALONG THE SOUTHWEST PRIPHERY OF THE STR. DUE TO THE BROAD NATURE OF THE LLCC AND THE MARGINALLY-FAVORABLE ENVIRONMENT, THE SYSTEM IS EXPECTED TO INTENSIFY AT A CLIMATOLOGICAL RATE THROUGH TAU 72. C. IN THE EXTENDED FORECAST PERIOD, AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH OVER THE KOREAN PENINSULA AND WESTERN JAPAN WILL ERODE THE WESTERN PERIPHERY OF THE STR, WHICH WILL ALLOW TY 17W TO MAINTAIN A NORTHWESTWARD TRACK TOWARD IWO TO. AVAILABLE MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. AFTER TAU 120, CURRENT GUIDANCE SUPPORTS A RE-CURVE SCENARIO TOWARD WESTERN OR CENTRAL JAPAN ALTHOUGH THERE IS CURRENTLY A HIGH DEGREE OF UNCERTAINTY IN THE EXACT TIMING OF THE RE-CURVE.// NNNN NNNN