WDPN31 PGTW 202100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (KROVANH) WARNING NR 004// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 26W (KROVANH), LOCATED APPROXIMATELY 447 NM EAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WEST- SOUTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS MULTIPLE VORTICES FORMING WITHIN A BROAD LOW-LEVEL CIRCULATION (LLC) WITH ISOLATED DEEP CONVECTION FLARING ALONG THE SOUTHWEST QUADRANT. A 201402Z MHS 89GHZ COMPOSITE IMAGE INDICATES A BROAD, DISORGANIZED LLC WITH FRAGMENTED SHALLOW BANDING WRAPPING AROUND THE LLC AND NO DEEP CONVECTIVE BANDING. A 201401Z ASCAT-B IMAGE ALSO SHOWS AN ELONGATED CIRCULATION, ORIENTED NNE-SSW, WITH TWO DISCRETE CIRCULATIONS ADJACENT TO EXTENSIVE 30-35 KNOT NORTHEASTERLY SURGE WINDS. THE INITIAL POSITION IS EXTRAPOLATED FROM THE NORTHERN CIRCULATION POSITION IN ASCAT IMAGERY. THE INITIAL INTENSITY REMAINS ASSESSED AT 30 KNOTS BASED ON THE OVERALL WIND FIELD / WEAK CONVECTIVE STRUCTURE, AND T1.0-1.5 (25 KNOTS) DVORAK SUBJECTIVE ESTIMATES AND A 201830Z ADT OBJECTIVE ESTIMATE OF 2.3 (33 KNOTS). UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT WITH HIGH (25 KNOTS) VERTICAL WIND SHEAR OFFSET BY STRONG POLEWARD OUTFLOW. SST VALUES (28-29C) REMAIN CONDUCIVE. THE SYSTEM IS TRACKING SLOWLY WEST-SOUTHWESTWARD ALONG THE SOUTHEAST PERIPHERY OF A LOW-LEVEL SUBTROPICAL RIDGE POSITIONED TO THE NORTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 26W IS EXPECTED TO TRACK WEST-SOUTHWESTWARD TO WESTWARD ALONG THE SOUTHERN FLANK OF THE LOW-LEVEL STR THROUGH TAU 72. THE SYSTEM IS FORECAST TO INTENSIFY SLIGHTLY OVER THE NEXT 12-24 HOURS AS VWS DECREASES TO MODERATE LEVELS (15 KNOTS) WITH PERSISTENT POLEWARD OUTFLOW. AFTER TAU 24, TD 26W SHOULD WEAKEN STEADILY AS IT TRACKS AWAY FROM THE STRONG SURGE FLOW AND UPPER-LEVEL DIVERGENCE DECREASES. THE SYSTEM IS FORECAST TO DISSIPATE SOUTH OF VIETNAM BY TAU 72. THE BULK OF NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC FORECAST TRACK, HOWEVER, THERE IS LOW OVERALL CONFIDENCE IN THE TRACK DUE TO HIGH UNCERTAINTY IN THE INITIAL POSITION.// NNNN