MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (KIROGI) WARNING NR 17// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 13W (KIROGI), LOCATED APPROXIMATELY 830 NM EAST- SOUTHEAST OF MISAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A 081732Z SSMI 85 GHZ MICROWAVE IMAGE DEPICT A SLIGHTLY ELONGATED LOW- LEVEL CIRCULATION CENTER (LLCC) ORIENTED FROM NW TO SE WITH A SMALL AREA OF CONVECTION OVER THE SOUTHERN SEMI-CIRCLE. A PARTIAL 081148Z OSCAT AND A 081815Z ASCAT SATELLITE IMAGE ALSO INDICATE A SLIGHTLY ELONGATED LLCC WITH 30-35 KNOT WINDS. ACCORDING TO A RECENT (080900Z) AMSU CROSS-SECTION, A +2 DEGREE CELSIUS WARM-CORE ANOMALY CENTERED NEAR 11 KM PERSISTS. THE CURRENT INTENSITY IS SLIGHTLY HIGHER THAN PGTW AND RJTD DVORAK INTENSITY ESTIMATES OF 30 KNOTS BASED ON RECENT SCATTEROMETRY. UPPER-LEVEL ANALYSIS INDICATES THAT TS 13W IS LOCATED SOUTH OF THE SUBTROPICAL RIDGE (STR) CENTER WITH A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE SOUTH. VERTICAL WIND SHEAR IS CURRENTLY AT 10-15 KNOTS, AND UPPER-LEVEL DIVERGENCE IS MINIMAL WITH VERY WEAK OUTFLOW TO THE SOUTH INTO THE TUTT. RECENT ANIMATED WATER VAPOR IMAGERY CONTINUES TO SHOW A NARROW REGION OF POLEWARD OUTFLOW AS TS 13W TRACKS CLOSER TO AN UPPER-LEVEL SHORTWAVE TROUGH EAST OF JAPAN. TOTAL PRECIPITABLE WATER IMAGERY INDICATES THE SYSTEM IS BECOMING ELONGATED AND REMAINS CUT-OFF FROM ANY CONNECTION TO THE MARITIME TROPICAL AIR MASS. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 13W IS EXPECTED TO TRACK UNDER THE SOUTHWESTERN PERIPHERY OF THE STR, POSITIONED TO THE EAST, FOR THE REMAINDER OF THE FORECAST PERIOD. THE SYSTEM IS FORECAST TO TRACK OVER INCREASINGLY COOLER SEA SURFACE TEMPERATURES (< 25 CELSIUS) AT 38 DEGREES NORTH AFTER TAU 12 AND WILL BEGIN TO INTERACT WITH THE EASTERN PERIPHERY OF A SHORTWAVE TROUGH THAT IS EXPECTED TO DEEPEN EAST OF JAPAN. THIS SHORTWAVE TROUGH IS ASSOCIATED WITH THE SUBTROPICAL JET AND HAS WEAK BAROCLINICITY, THEREFORE, THE SYSTEM IS NOT EXPECTED TO UNDERGO EXTRA-TROPICAL TRANSITION AND SUBTROPICAL TRANSITION IS THE MOST LIKELY RESULT. ALTHOUGH THE FORECAST CONFIDENCE FOR THE TIMING OF SUBTROPICAL TRANSITION IS LOW, THE TRACK FORECAST CONFIDENCE REMAINS HIGH DUE TO TIGHTLY CLUSTERED OBJECTIVE AID GUIDANCE.// NNNN NNNN