MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (ELEVEN) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 11W (ELEVEN), LOCATED APPROXIMATELY 252 NM SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED WEST-SOUTHWESTWARD AT 07 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS MAINTAINED OVERALL STRUCTURE WITH FLARING DEEP CENTRAL CONVECTION SHEARED SOUTHWARD OF A RAGGED AND PARTIALLY EXPOSED LOW LEVEL CIRCULATION. THE INITIAL POSITION IS EXTRAPOLATED FROM THE MSI LOOP WITH FAIR CONFIDENCE. THE INITIAL INTENSITY OF 35 KTS IS BASED ON THE DVORAK ESTIMATE OF T2.5/35KTS FROM PGTW. ANALYSIS INDICATES TS 11W IS UNDER A MARGINAL ENVIRONMENT WITH STRONG EQUATORWARD UPPER LEVEL OUTFLOW AND WARM (30- 31 CELSIUS) SEA SURFACE TEMPERATURES (SST) THAT ARE GREATLY OFFSET BY MODERATE (20-25KT) NORTHEASTERLY VERTICAL WIND SHEAR (VWS). THE CYCLONE IS TRACKING UNDER THE COMBINED STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR) TO THE WEST AND AN EXTENSION OF THE STR TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE LAST PROGNOSTIC REASONING MESSAGE. B. TS 11W WILL CONTINUE ON ITS CURRENT TRACK UP TO TAU 24 WITH MINIMAL INTENSIFICATION TO 55 KTS DUE TO THE MARGINAL ENVIRONMENT. AFTERWARD, A MIDLATITUDE SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST WILL BEGIN TO ERODE THE STR TO THE WEST. THE STR TO THE NORTHEAST, ON THE OTHER HAND, WILL BUILD AND BECOME THE PRIMARY STEERING MECHANISM AND DRIVE THE SYSTEM SLOWLY WESTWARD THEN NORTHWESTWARD. VWS VALUES WILL DECREASE AFTER TAU 24 ALLOWING TS 11W TO STEADILY INTENSIFY ALONG THE FORECAST TRACK TO 95 KTS BY TAU 72. NUMERICAL MODELS ARE IN FAIR AGREEMENT BUT GIVEN THE COMPLEX STEERING, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST. C. BEYOND TAU 72, TS 11W WILL CONTINUE TO TRACK NORTHWESTWARD ALONG THE PERIPHERY OF THE DOMINANT STR TO THE EAST. THE SYSTEM WILL STEADILY INTENSIFY TO 120 KTS BY TAU 120 DUE TO CONTINUED FAVORABLE ENVIRONMENTAL CONDITIONS OF LOW VWS, WARM SST, AND CONDUCIVE OCEAN HEAT CONTENT VALUES. NUMERICAL MODELS ARE IN BETTER AGREEMENT IN THE LATER TAUS, LENDING HIGH CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST. NNNN NNNN