WDPN31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (KROVANH) 
WARNING NR 002//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 26W (TWENTYSIX), LOCATED APPROXIMATELY 485 NM 
EAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 
10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) DEPICTS A HIGHLY SHEARED, ASYMMETRIC, AND DISORGANIZED 
SYSTEM, WITH MULTIPLE EXPOSED, LOW LEVEL VORTICES WRAPPING AROUND 
THE BROADER CIRCULATION CENTER AND LIMITED FLARING CONVECTION 
DISPLACED NORTH AND WEST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). 
DUE TO THE PRESENCE OF MULTIPLE VORTICES, THE INITIAL POSITION IS 
PLACED WITH LOW CONFIDENCE IN THE ROUGH CENTROID OF THE LARGER 
CIRCULATION, CONSISTENT WITH RECENT AGENCY FIX POSITIONS FROM PGTW 
AND RJTD. THE INITIAL INTENSITY IS ASSESSED AT 30 KNOTS WITH LOW 
CONFIDENCE, HEDGED ABOVE THE SUBJECTIVE DVORAK INTENSITY ESTIMATES 
OF T1.0 (25 KNOTS) FROM PGTW AND T1.5 (25 KNOTS) FROM RJTD IN 
RECOGNITION OF HIGHER WINDS, PART OF PRE-EXISTING NORTHEAST SURGE 
FLOW, PRESENT TO THE NORTH AND WEST OF THE CIRCULATION. CONVERGENT 
LOW LEVEL FLOW BETWEEN THE NORTHEAST SURGE FLOW AND THE APPROACHING 
LLCC IS SUPPORTING THE GENERATION OF DEEP, FLARING CONVECTION TO THE 
NORTHWEST OF THE CIRCULATION. ENVIRONMENTAL CONDITIONS ARE 
MARGINALLY FAVORABLE FOR DEVELOPMENT, WITH MODERATE TO HIGH (20-25 
KTS) VERTICAL WIND SHEAR (VWS), VERY WARM SEA SURFACE TEMPERATURES 
(28-29C), AND STRONG DIVERGENT, POLEWARD OUTFLOW ALOFT. WHILE THE 
OVERALL ENVIRONMENT IS SUPPORTIVE OF ADDITIONAL DEVELOPMENT, THE 
HIGH VWS IS CURRENTLY INHIBITING THE CONSOLIDATION OF THE CORE, AS 
REFLECTED BY THE SHEARED NATURE OF THE CONVECTION. THE SYSTEM IS 
TRACKING GENERALLY WESTWARD FOLLOWING THE FLOW ASSOCIATED WITH A LOW 
TO MID-LAYER STEERING RIDGE TO THE NORTH. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 26W IS EXPECTED TO CONTINUE TRACKING GENERALLY WEST-
SOUTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STEERING RIDGE 
ENTRENCHED TO THE NORTH THROUGH TAU 48. SLOW INTENSIFICATION IS 
FORECAST THROUGH TAU 24 AS THE SYSTEM AS THE WINDS ASSOCIATED WITH 
THE NORTHEAST SURGE FLOW BEGIN TO WRAP AROUND THE SOUTHERN SIDE OF 
THE LLCC AND ROBUST DIVERGENT OUTFLOW ALOFT OFFSETS MODERATE VWS. A 
SLIGHT REORIENTATION OF THE UPPER-LEVEL FLOW PATTERN WILL LEAD TO 
MORE CONVERGENT OUTFLOW ALOFT, COMBINED WITH PERSISTENT MODERATE 
VWS, DECREASING SSTS, AND A SEPARATION FROM THE NORTHEAST SURGE 
FLOW, WILL LEAD TO A WEAKENING TREND FROM TAU 36 THROUGH THE 
REMAINDER OF THE FORECAST PERIOD. AS THE SYSTEM BEGINS TO WEAKEN, IT 
WILL ALSO SHIFT TO A MORE WESTWARD TRACK AS IT COMES UNDER THE 
STEERING INFLUENCE OF THE LOWER-LEVEL FLOW. NUMERICAL MODEL GUIDANCE 
IS IN GOOD AGREEMENT WITH THE OVERALL TRACK FORECAST SCENARIO, WITH 
SMALL SPREAD THROUGH TAU 48. BEYOND TAU 48, MODEL GUIDANCE SHOWS 
INCREASING UNCERTAINTY, WITH THE NAVGEM, UKMET AND GFS ENSEMBLES 
SHOWING A TRACK OVER FAR SOUTHERN VIETNAM, WHICH THE REMAINDER OF 
TRACK GUIDANCE KEEPS THE CENTER OF CIRCULATION WELL OFFSHORE 
SOUTHERN VIETNAM. OVERALL, IN LIGHT OF THE UNCERTAINTY IN THE 
INITIAL POSITION, AND SUBSEQUENT UNCERTAINTY IN THE AMOUNT OF AND 
TIMING OF THE INTERACTION WITH THE NORTHEAST SURGE FLOW, AND IMPACT 
THAT ON THE TRACK, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC 
FORECAST THROUGH TAU 72. 
   C. TD 26W IS EXPECTED TO FULLY DISSIPATE BY TAU 96 AS IT 
CONTINUES TRACKING WESTWARD AROUND THE SOUTHERN TIP OF VIETNAM INTO 
THE SOUTHERN GULF OF THAILAND.//
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