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.//
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