WDPN31 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING 
NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 09W (NINE), LOCATED APPROXIMATELY 220 NM 
SOUTHEAST OF HONG KONG, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS 
THE DEEP CONVECTIVE BANDING WRAPPING ALONG THE SOUTHERN AND WESTERN 
SECTORS HAS PERSISTED OVER THE PAST 12 HOURS. THE LOW LEVEL 
CIRCULATION CENTER (LLCC) HAS BEEN SLOWLY ORGANIZING AS THE SYSTEM 
TRACKS ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYERED SUBTROPICAL 
RIDGE (STR) ANCHORED OVER SOUTHEAST ASIA. UPPER LEVEL ANALYSIS 
CONTINUES TO SHOW A MINOR ANTICYCLONE BUILDING OVER THE LLCC, 
SUPPORTING THE EQUATORIAL VENTING OF THE SYSTEM. THE ANTICYCLONE IS 
DISLOCATED SLIGHTLY TO THE NORTH OF THE LLCC, WHICH IS HINDERING 
CONVECTIVE DEVELOPMENT ALONG THE NORTHEASTERN QUADRANT DUE TO THE 
MODERATE VERTICAL WIND SHEAR. THE CURRENT INTENSITY IS BASED ON THE 
RECENT INCREASE IN CONVECTION AND DVORAK ESTIMATES FROM PGTW, RJTD, 
AND KNES. BASED ON THE POOR ORGANIZATION OF THE LLCC AND A LACK OF 
DATA SUPPORTING THE CURRENT POSITION, THERE IS LOW CONFIDENCE IN THE 
POSITIONING OF THE LLCC.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 09W WILL CONTINUE TO TRACK WESTWARDS UNDER THE SOUTHERN 
PERIPHERY OF A BUILDING, ZONAL ORIENTATED, STR FOR THE ENTIRE 
FORECAST PERIOD. THE DEVELOPING UPPER LEVEL ANTICYCLONE AND 
FAVORABLE SEA SURFACE TEMPERATURES (SSTS) (28-30 CELSIUS) WILL ALLOW 
FOR TD 09W TO STEADILY INCREASE IN INTENSITY AS IT TRACKS INTO THE 
GULF OF TONKIN. THE SYSTEM IS EXPECTED TO TRACK OVER THE LUICHOW 
PENINSULA WHICH WILL BRIEFLY HINDER DEVELOPMENT BETWEEN TAU 60 AND 
TAU 72.
   C. IN THE EXTENDED FORECAST, TD 09W SHOULD BE ABLE TO MAINTAIN 
TROPICAL STORM STRENGTH AS IT TRACKS OVER THE NORTHERN WATERS OF THE 
GULF OF TONKIN. BASED ON THE CLOSE PROXIMITY TO LAND BEYOND TAU 72, 
THE INTENSITY IS NOT EXPECTED TO INCREASE AS IT BRIEFLY CROSSES THE 
GULF, MAKING LANDFALL IN NORTHERN VIETNAM BY TAU 96. DISSIPATION IS 
EXPECTED TO BEGIN AS THE SYSTEM MAKES LANDFALL AND SHOULD BE 
COMPLETED DISSIPATED BY TAU 120. NUMERICAL MODEL GUIDANCE REMAINS 
TIGHTLY CLUSTERED, HOWEVER THE CURRENT FORECAST REMAINS SOUTH OF THE 
CONSENSUS OF MODEL GUIDANCE BASED ON THE EXPECTED POSITIONING OF THE 
STR CURRENTLY STEERING THE SYSTEM. DUE TO THE TIGHT GUIDANCE 
ENVELOPE THERE IS HIGH CONFIDENCE IN THE OFFICIAL JTWC TRACK 
FORECAST. HOWEVER, SINCE THE CURRENT POSITION CONFIDENCE IS LOW A 
SLIGHT ADJUSTMENT IN THE SHORT-TERM MAY BE NEEDED IN SUBSEQUENT 
FORECASTS, BUT THE OVERALL WESTWARDS FORECAST TRACK IS WELL 
SUPPORTED BY THE SYNOPTIC ENVIRONMENT AND MODEL DEPICTION.//
NNNN