MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (LAN) WARNING NR 03// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 25W (LAN), LOCATED APPROXIMATELY 156 NM WEST- NORTHWEST OF YAP, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS DEEP CONVECTION WRAPPING AROUND THE SOUTHERN AND EASTERN QUADRANTS OF A GRADUALLY ORGANIZING LOW-LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE NEAR OVERSHOOTING TOPS VISIBLE IN THE MSI. THE INITIAL INTENSITY IS SET AT 35 KNOTS BASED ON A DVORAK ESTIMATE OF T2.5 FROM PGTW. UPPER- LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF MODERATE VERTICAL WIND SHEAR (20-25 KNOTS), BUT IS SITUATED ALONG A SHEAR GRADIENT, WHICH IS INDICATIVE OF DECENT POLEWARD OUTFLOW. SEA SURFACE TEMPERATURES REMAIN WARM (30 DEGREES C) AS THE SYSTEM TRACKS TOWARD THE NORTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 25W WILL CONTINUE TO TRACK TOWARD THE NORTHWEST IN THE SHORT TERM. AFTER 24 TO 36 HOURS, THE SYSTEM IS EXPECTED TO TURN TOWARD THE NORTH IN RESPONSE TO A MID-LATITUDE TROUGH DIGGING THROUGH JAPAN AS THE STEERING SUBTROPICAL RIDGE (STR) AMPLIFIES TOWARD THE EAST. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST AND ALLOW FOR STEADY INTENSIFICATION. BY TAU 72, TS 25W IS EXPECTED TO BECOME A 90 KNOT SYSTEM. C. AFTER TAU 72, TS 25W WILL CONTINUE ITS NORTHWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST, WITH A GRADUAL TURN TOWARD THE NORTH-NORTHEAST AT LATER TAUS. GIVEN WARM SEA SURFACE TEMPERATURES AND FAVORABLE UPPER-LEVEL CONDITIONS, A PERIOD OF RAPID INTENSIFICATION REMAINS A POSSIBILITY AS THE SYSTEM GAINS LATITUDE AND UPPER-LEVEL OUTFLOW IS ENHANCED BY SYNOPTIC FORCING AHEAD OF THE MID-LATITUDE TROUGH. GLOBAL MODELS ARE IN GOOD AGREEMENT WITH THE GENERAL NORTHWARD MOTION, ALTHOUGH THE TIMING OF THE TURN IS STILL A BIT UNCERTAIN. FURTHERMORE, THE GFS AND NAVGEM SUGGEST THAT MULTIPLE CIRCULATIONS COULD FORM ON THE EASTERN PERIPHERY OF TS 25W, WHICH WOULD COMPLICATE THE DYNAMICS. ON THE OTHER HAND, THE ECMWF SUGGESTS THAT TS 25W WILL REMAIN THE DOMINANT CIRCULATION. THUS, THERE IS GOOD CONFIDENCE IN THE INITIAL JTWC TRACK FORECAST, BUT LOW CONFIDENCE THEREAFTER UNTIL THE FUTURE STRUCTURE OF TS 25W BECOMES MORE CERTAIN.// NNNN NNNN