MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (FENGSHEN) WARNING NR 004// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 26W (FENGSHEN), LOCATED APPROXIMATELY 924 NM EAST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD, EXPOSED LOW LEVEL CIRCULATION (LLC) WITH AN AREA OF DEEP CONVECTION SHEARED TO THE WEST. THE POSITION IS BASED ON MSI AND A 120621Z SSMIS 91GHZ COMPOSITE IMAGE AND IS PLACED WITH FAIR CONFIDENCE. THE CURRENT INTENSITY OF 30 KNOTS IS BASED ON A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF 2.0/30KTS. TROPICAL DEPRESSION FENGSHEN IS TRAVELING ALONG THE SOUTHERN PORTION OF THE SUBTROPICAL RIDGE (STR) AND IS IN A MARGINALLY FAVORABLE AREA FOR FURTHER DEVELOPMENT WITH WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURES, MARGINAL (15-20 KNOTS) VERTICAL WIND SHEAR (VWS) AND EASTERLY OUTFLOW ALOFT. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 26W WILL CONTINUE TO TRACK GENERALLY WEST-NORTHWESTWARD UNDER THE STR UP TO TAU 60 WHEN IT WILL BEGIN TO CURVE POLEWARD. THE FAVORABLE ENVIRONMENTAL CONDITIONS WILL GRADUALLY INTENSIFY THE SYSTEM TO 80 KNOTS BY TAU 72. NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH TAU 72 WITH ECMWF THE SOLE OUTLIER AS IT SHOWS VERY WEAK DEVELOPMENT OF THE SYSTEM PAST TAU 48. OTHERWISE, THERE IS GOOD AGREEMENT BETWEEN THE OTHER MEMBERS OF THE MULTI-MODEL CONSENSUS LENDING A HIGH DEGREE OF CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. AFTER TAU 72, TD 26W WILL RECURVE TOWARDS THE NORTH-NORTHEAST AND GRADUALLY WEAKEN IN RESPONSE TO THE MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST AND THE STRONG WESTERLY FLOW IT WILL ENCOUNTER. IT WILL THEN CREST THE STR AXIS AND ACCELERATE EAST- NORTHEASTWARD ALONG THE NORTH SIDE OF THE STR. STRONG WESTERLY WINDS WILL PRODUCE INCREASINGLY UNFAVORABLE VWS (25-40 KNOTS). THIS, ALONG WITH SLIGHTLY COOLER SSTS, WILL RESULT IN A MORE SIGNIFICANT REDUCTION IN INTENSITY. BY TAU 96, TD 26W WILL BEGIN EXTRA-TROPICAL TRANSITION AS IT BEGINS TO INTERACT WITH THE BAROCLINIC ZONE. NUMERICAL MODELS DIVERGE AND ARE IN POOR AGREEMENT LENDING LOW OVERALL CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN