WDPN31 PGTW 090300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (KIROGI) WARNING NR 18// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 13W (KIROGI), LOCATED APPROXIMATELY 745 NM EAST-SOUTHEAST OF MISAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A 082149Z SSMIS 91 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 082244Z ASCAT SATELLITE IMAGE INDICATES WINDS ALONG THE EASTERN PERIPHERY ARE BETWEEN 25 TO 30 KNOTS. THE MOST RECENT AMSU CROSS-SECTION (081500Z) SHOWS THE +2 DEGREE CELSIUS WARM-CORE ANOMALY REMAINS PERSISTENT NEAR 10 TO 11 KM. THE CURRENT INTENSITY OF 30 KNOTS IS BASED ON THE ASCAT PASS AND A RANGE OF DVORAK ESTIMATES FROM 25 TO 35 KNOTS FROM PGTW, RJTD, AND KNES. UPPER-LEVEL ANALYSIS INDICATES THAT TD 13W IS LOCATED SOUTH OF THE SUBTROPICAL RIDGE (STR) AXIS 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 TD 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. TD 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 (SST) (< 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. QUICKLY DECREASING SSTS WILL CAUSE A TRANSITION FROM WARM- CORE TROPICAL TO A COLD-CORE SUBTROPICAL LOW. 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