MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 13// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY 44 NM EAST OF ANDERSEN AFB, GUAM HAS TRACKED WEST-NORTHWESTWARD AT 17 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY CONTINUES TO SHOW TIGHTLY-CURVED BANDING WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER. THE CURRENT POSITION IS BASED ON THE EIR LOOP AND ON RADAR FIXES FROM NWS GUAM WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 90 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES AN AREA OF SUBSIDENCE IS LOCATED NORTH OF THE SYSTEM IMPACTING THE CURRENT DEVELOPMENT. ADDITIONALLY, TY 19W IS NOW LOCATED IN AN AREA OF MODERATE (10 TO 20 KNOT) VERTICAL WIND SHEAR (VWS) OFFSET BY EXCELLENT EQUATORWARD OUTFLOW. TY 19W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 19W WILL CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR THROUGH TAU 72. UPPER-LEVEL CONDITIONS WILL IMPROVE SLOWLY LEADING TO A GRADUAL INTENSIFICATION AND REACHING 130 KNOTS BY TAU 72. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT LENDING HIGH CONFIDENCE TO THE FIRST 72 HOURS OF THE FORECAST. C. TY VONGFONG IS EXPECTED TO TRACK ON A MORE POLEWARD DIRECTION AS THE STR WEAKENS IN RESPONSE TO A MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST. THE SYSTEM WILL BEGIN TO WEAKEN AFTER TAU 96, AS VWS INCREASES. AVAILABLE MODEL GUIDANCE REMAINS SIGNIFICANTLY SPREAD DURING THIS PORTION OF THE FORECAST, LENDING LOW CONFIDENCE IN THE JTWC TRACK FORECAST BEYOND TAU 72.// NNNN NNNN