WDPN31 PGTW 210900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (KROVANH) WARNING NR 006// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 26W (KROVANH), LOCATED APPROXIMATELY 373 NM EAST-SOUTHEAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WEST- SOUTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD, DISORGANIZED LOW-LEVEL CIRCULATION (LLC) WITH WELL-DEFINED CLOUD BANDS MOVING RAPIDLY SOUTHWARD TO THE WEST OF THE LLC, AND MULTIPLE VORTICES ROTATING CYCLONICALLY AROUND THE LLC, PARTICULARLY IN THE SOUTH AND SOUTHEAST QUADRANTS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON ANALYSIS OF THE LOW-LEVEL BANDING FEATURES EVIDENT IN A 210551Z AMSR2 36GHZ MICROWAVE IMAGE, WHICH ALSO DEPICTS THE FRAGMENTED NATURE OF THE CONVECTIVE BANDING, LIMITED PRIMARILY TO THE NORTH AND NORTHEAST PORTION OF THE CIRCULATION. THE INITIAL INTENSITY HAS BEEN LOWERED TO 25 KNOTS WITH FAIR CONFIDENCE, BASED ON THE OVERALL WEAK STRUCTURE OF THE SYSTEM, AND T1.0-1.5 (25 KNOTS) DVORAK SUBJECTIVE ESTIMATES AND AN ADT OBJECTIVE ESTIMATE OF 2.2 (32 KNOTS). AN EARLIER 210238Z ASCAT-B SCATTEROMETER PASS INDICATED THAT WHILE THERE ARE WINDS UP TO 30-35 KNOTS HUGGING THE COAST OF VIETNAM, THESE ARE NOT WRAPPING INTO THE CIRCULATION AT THIS TIME. THE OVERALL ENVIRONMENT REMAINS MARGINAL, WITH MODERATE TO HIGH (20- 25 KTS) VWS BEING SOMEWHAT OFFSET BY ROBUST, DIVERGENT, POLEWARD OUTFLOW, AND WARM (28-29C) SSTS. 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 PERIPHERY OF THE LOW-LEVEL STR TO THE NORTH THROUGH THE DURATION OF THE FORECAST. A SHORT PERIOD OF INTENSIFICATION IS EXPECTED THROUGH TAU 24, AS THE SYSTEM MOVES FURTHER WEST AND EXPERIENCES ENHANCED INTERACTION WITH THE PRE- EXISTING STRONG NORTHEASTERLY FLOW, IT BECOMES PINNED AGAINST THE VIETNAM COASTLINE, ENTRAINING AND WRAPPING PROGRESSIVELY HIGHER WINDS INTO THE CORE CIRCULATION. DECREASING VWS AND PERSISTENT UPPER- LEVEL OUTFLOW WILL PROVIDE ADDITIONAL SUPPORT FOR THE SHORT PERIOD OF INTENSIFICATION. AFTER TAU 24, TD 26W WILL STEADILY WEAKEN AND DISSIPATE OVER WATER BY TAU 48 AS IT SEPARATES FROM THE NORTHEASTERLY SURGE FLOW, VWS INCREASES AND UPPER-LEVEL OUTFLOW DECREASES. WITH THE EXCEPTION OF THE UKMET ENSEMBLE, THE REMAINDER OF THE NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT, LENDING OVERALL HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN