MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEOGURI) WARNING NR 007// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (NEOGURI), LOCATED APPROXIMATELY 408 NM SOUTH-SOUTHEAST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 06 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY REVEALS DEEP CONVECTION OBSCURING A LOW LEVEL CIRCULATION CENTER. THE POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON AN 180050Z METOP-B ASCAT PASS AND AN 180048Z AMSU 89GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY OF 45 KTS IS SET WITH GOOD CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT PASS. THIS INTENSITY IS SLIGHTLY BELOW THE 180110Z ADVANCED DVORAK TECHNIQUE ESTIMATE OF 51 KTS. THE ENVIRONMENT IS FAVORABLE WITH LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), GOOD POLEWARD OUTFLOW, AND WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE (SST). TS 21W IS TRACKING SLOWLY NORTHWESTWARD AROUND THE SOUTHWEST PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE LAST PROGNOSTIC REASONING MESSAGE. B. IN THE NEAR TERM, TS 21W IS EXPECTED TO MAINTAIN A NORTHWESTERLY TRACK UNTIL TAU 48 WHEN IT ROUNDS THE STR AXIS. THERE IS SIGNIFICANT UNCERTAINTY IN THE TIMING AND STRENGTH OF THE STR. DUE TO THIS UNCERTAINTY, THERE IS POOR CONFIDENCE IN TRACK GUIDANCE AS THERE IS A 320 NM SPREAD BETWEEN TRACK MEMBERS BY TAU 72. UNTIL THIS POINT IN THE FORECAST, THE UPPER LEVEL ENVIRONMENT HAS LIMITED THE INTENSIFICATION OF TS 21W. HOWEVER, WITH THE APPROACHING TROUGH TO THE NORTHWEST, THE POLEWARD OUTFLOW MAY STRENGTHEN AND CAUSE A SLIGHT INTENSIFICATION TO 50 KTS BY TAU 24. TS 21W IS EXPECTED TO CROSS THE STR AXIS BY TAU 72 AND BEGIN RECURVING TO THE NORTHEAST. OVERALL, GLOBAL MODELS HAVE MAINTAINED THE RECURVE SCENARIO, WITH EXCEPTION OF NAVGEM AND ECMWF . THE JTWC TRACK FORECAST IS PLACED NEAR THE CONSENSUS. DUE TO THE AFOREMENTIONED FACTORS, THERE IS OVERALL LOW TRACK AND INTENSITY CONFIDENCE IN THIS PORTION OF THE FORECAST. C. BEYOND TAU 72, TS 21W IS EXPECTED TO RECURVE AS THE APPROACHING TROUGH WEAKENS THE STR AND TS 21W ENCOUNTERS SOUTHWESTERLY FLOW. TS 21W IS CURRENTLY EXPECTED TO ENCOUNTER INCREASED SHEAR WHICH WILL LIKELY WEAKEN TS 21W ALONG ITS NORTHEAST TRACK. WITH SPREAD EXCEEDING 730 NM BY TAU 120, THERE IS LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.// NNNN NNNN