MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (TWENTYSIX) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 26W (TWENTYSIX), LOCATED APPROXIMATELY 770 NM EAST OF IWO TO, JAPAN, HAS TRACKED NORTHWESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE MAIN CONVECTION IS SHEARED TO THE SOUTHWEST, PARTIALLY EXPOSING A BROAD AND ELONGATED LOW LEVEL CIRCULATION. THE INITIAL POSITION IS BASED ON THE MSI ANIMATION WITH LOW CONFIDENCE. THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF MODERATE (15-20 KNOT) VERTICAL WIND SHEAR (VWS) THAT IS OFFSET BY GOOD EQUATORWARD OUTFLOW. THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A LOW- TO MID-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN AND SETS THE FORECAST PHILOSOPHY ON THIS SYSTEM. B. TD 26W IS EXPECTED TO TRACK NORTH AND BEGIN ROUNDING THE WESTERN EDGE OF THE STEERING STR OVER THE NEXT 12 HOURS. AFTERWARDS, IT WILL ACCELERATE NORTHEASTWARD AS IT GETS EMBEDDED IN THE MID-LATITUDE WESTERLIES. INCREASED POLEWARD OUTFLOW WILL OFFSET INCREASING VWS AND SUSTAIN THE SYSTEM AT TD INTENSITY THROUGHOUT THE FORECAST PERIOD. BY TAU 12, THE CYCLONE WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT ENTERS THE COLD BAROCLINIC ZONE, BECOMING A COLD CORE LOW BY TAU 48. THERE IS, HOWEVER, A DISTINCT POSSIBILITY THAT THE SYSTEM WILL DISSIPATE PRIOR TO ETT DUE TO HIGH VWS. THE AVAILABLE NUMERIC GUIDANCE IS IN GOOD AGREEMENT. HOWEVER, GIVEN THE BROAD AND WEAK LOW LEVEL STRUCTURE AND THE UNCERTAINTY IN THE FORECAST INTENSITY, THERE IS AN OVERALL LOW CONFIDENCE IN THE INITIAL JTWC FORECAST.// NNNN NNNN