WDPN33 PGTW 140300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (NANGKA) 
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (NANGKA), LOCATED APPROXIMATELY 78 NM 
SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED WESTWARD AT 20 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS 
THE SYSTEM CONTINUED TO ACCELERATE OVER THE GULF OF TONKIN AND HAS 
OVERALL MAINTAINED ITS DEGREE OF CONVECTIVE WRAP INTO A TIGHT AND WELL-
DEFINED LOW LEVEL CIRCULATION (LLC) EVEN AS THE FEEDER AND CENTRAL 
CONVECTION ON THE FORWARD SIDE HAVE BEGUN TO ERODE DUE LAND INTERACTION 
WITH VIETNAM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED 
ON THE LLC FEATURES IN THE MSI LOOP AND A COMPOSITE RADAR LOOP FROM 
CNA. THE INITIAL INTENSITY OF 45KTS IS BASED ON THE HIGH END OF AGENCY 
DVORAK ESTIMATES OF T2.5/35KTS TO T3.0/45KTS TO REFLECT THE SUSTAINED 
TIGHT WRAP. ENVIRONMENTAL ANALYSIS INDICATES THE SYSTEM REMAINS IN A 
GENERALLY FAVORABLE ENVIRONMENT WITH LOW (10-15KT) VERTICAL WIND SHEAR, 
DIVERGENT WESTWARD OUTFLOW, AND WARM (29C) SST. HOWEVER, THESE ARE 
OFFSET BY THE FRICTIONAL AND DRYING EFFECTS OF THE INDOCHINA PENINSULA. 
THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED 
SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS NANGKA WILL CONTINUE TO TRACK WESTWARD IN THE GULF OF TONKIN 
UNDER THE STR AND MAKE A FINAL LANDFALL OVER NORTHERN VIETNAM BY TAU 
06. AFTERWARD, LAND INTERACTION WILL RAPIDLY ERODE THE SYSTEM TO 
DISSIPATION BY TAU 36, POSSIBLY SOONER, AFTER IT DRAGS ACROSS THE 
RUGGED TERRAIN OF NORTHERN VIETNAM AND LAOS. NUMERICAL MODELS REMAIN IN 
TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.//
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