MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (ELEVEN) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 11W (ELEVEN), LOCATED APPROXIMATELY 256 NM SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED SOUTHWESTWARD AT 12 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS FLARING DEEP CENTRAL CONVECTION SHEARED SOUTHWESTWARD OF A PARTIALLY EXPOSED LOW LEVEL CIRCULATION. THE INITIAL POSITION IS EXTRAPOLATED FROM THE EIR LOOP AND FROM A NOTCH FEATURE IN THE 311625Z AMSR2 MICROWAVE IMAGE WITH LOW CONFIDENCE. THE INITIAL INTENSITY OF 35KTS IS BASED ON THE DVORAK ESTIMATE OF T2.5/35KTS FROM PGTW AND REFLECTS THE IMPROVED EIR SIGNATURE. 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 BEING 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 55KTS 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 95KTS BY TAU 72. NUMERICAL MODELS ARE IN FAIR AGREEMENT BUT GIVEN THE COMPLEX STEERING AND THE FORMATIVE NATURE OF THE CYCLONE, 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 115 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 FAIR AGREEMENT IN THE LATER TAUS, HOWEVER, GIVEN THE INITIAL TRACK UNCERTAINTY, THERE IS ALSO A LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST. NNNN NNNN