Tropical Storm NANGKA Advisory 10月13日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (NANGKA)
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (NANGKA), LOCATED APPROXIMATELY 235 NM
SOUTH-SOUTHWEST OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY SHOWS A SLOWLY CONSOLIDATING SYSTEM WITH
FRAGMENTED RAIN BANDS FEEDING IN FROM THE SOUTH INTO A LOW LEVEL
CIRCULATION THAT IS OBSCURED BY A SLIGHTLY-DEEPENED CENTRAL
CONVECTION. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE
BASED ON THE EIR AND COMPOSITE RADAR LOOPS. THE INITIAL INTENSITY OF
40KTS IS HELD A TAD HIGHER THAN THE PGTW AND RJTD DVORAK INTENSITY
ESTIMATES OF T2.5/35KTS TO REFLECT THE CONSOLIDATION. UPPER-LEVEL
ANALYSIS INDICATES AN OVERALL FAVORABLE ENVIRONMENT WITH LOW
VERTICAL WIND SHEAR AND GOOD EQUATORWARD OUTFLOW. ADDITIONALLY, SST
(29-30C) VALUES IN THE SOUTH CHINA SEA ARE ALSO CONDUCIVE FOR
DEVELOPMENT. TS 18W 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. THE STR WILL CONTINUE TO DRIVE TS NANGKA ON ITS CURRENT TRACK
FOR THE ENTIRE FORECAST PERIOD, MAKING LANDFALL OVER HAINAN, CHINA,
SHORTLY AFTER TAU 12, CROSS THE GULF OF TONKIN (GOT), THEN MAKE A
FINAL LANDFALL OVER NORTHERN VIETNAM NEAR TAU 42. THE FAVORABLE
ENVIRONMENT WILL FUEL A MODEST INTENSIFICATION TO 45KTS BY TAU 12
JUST BEFORE LANDFALL INTO HAINAN. AFTERWARD, LAND INTERACTION WILL
REDUCE THE INTENSITY TO 40KTS AS TS 18W EXITS INTO THE GOT. THE WARM
SST IN THE GOT WILL PROMOTE A SECONDARY INTENSIFICATION TO 45KTS BY
TAU 48 BEFORE LANDFALL INTO VIETNAM. AFTER LANDFALL, THE SYSTEM WILL
RAPIDLY ERODE DUE TO FRICTIONAL EFFECTS FROM THE RUGGED TERRAIN,
LEADING TO DISSIPATION BY TAU 72. NUMERICAL MODELS ARE IN TIGHT
AGREEMENT WITH MINIMAL SPREADING AFTER TAU 36. THE JTWC FORECAST
TRACK LIES NEAR THE MULTI-MODEL CONSENSUS WITH OVERALL HIGH
CONFIDENCE.//
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