Tropical Storm NAMTHEUN Advisory 03 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 10//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (NAMTHEUN), LOCATED APPROXIMATELY 281 NM SOUTH OF
SASEBO, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
COMPACT SYSTEM THAT HAS MAINTAINED DEEP CONVECTIVE SIGNATURE AND A
10-NM EYE. THE INITIAL POSITION IS BASED ON THE EYE FEATURE IN THE
EIR LOOP AND ON COMPOSITE RADAR REFLECTIVITY LOOP FROM THE JAPAN
METEOROLOGICAL AGENCY WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF
100 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF OBJECTIVE AND AGENCY
FIXES RANGING FROM T5.0 TO T5.5. FAVORABLE ENVIRONMENTAL CONDITIONS
WITH SSTS NEAR 29C, HIGH OCEAN HEAT CONTENT, AND STRONG POLEWARD
OUTFLOW ARE BEING OFFSET BY INCREASING VERTICAL WIND SHEAR (VWS). THE
CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W IS FORECAST TO CONTINUE TRACKING NORTHWARD ALONG THE
WESTERN PERIPHERY OF THE STR MAKING LANDFALL ALONG THE WESTERN,
CENTRAL COAST OF KYUSHU SOUTH OF SASEBO NEAR TAU 30. AFTER TAU 36,
THE SYSTEM WILL TURN NORTHEASTWARD AS IT ROUNDS THE STR AXIS, WITH
CLOSEST POINT OF APPROACH TO SASEBO AT APPROXIMATELY 26 NM.
INCREASING VWS THEN LAND INTERACTION WILL GRADUALLY WEAKEN THE
SYSTEM, HOWEVER, IT WILL STILL BE AT TYPHOON INTENSITY AT TAU 36 AS
IT APPROACHES SASEBO. RAPID DECAY WILL COMMENCE ONCE THE SYSTEM GOES
BACK OVER COLDER WATER (LESS THAN 25C)IN THE SEA OF JAPAN, IN
ADDITION TO VERY STRONG VWS (GREATER THAN 40 KNOTS). BY TAU 72, TY
15W WILL BEGIN EXTRA-TROPICAL TRANSITION.
    C. IN THE EXTENDED TAUS, TY NAMTHEUN WILL ACCELERATE
NORTHEASTWARD AND DEEPER INTO THE COLD BAROCLINIC ZONE, BECOMING A
COLD-CORE LOW WITH MODERATE GALE-FORCE WINDS BY TAU 96. NUMERIC MODEL
GUIDANCE IS IN TIGHT AGREEMENT WITH NAVGEM ON THE EXTREME LEFT OF THE
PACK IN THE NEAR TERM THEN CROSSING THE ENVELOPE TO THE EXTREME RIGHT
IN THE LONG TERM. THE JTWC TRACK FORECAST HAS BEEN ADJUSTED TO
COMPENSATE THIS ERRATIC VORTEX MOTION. OVERALL, CONFIDENCE IN THE
JTWC FORECAST REMAINS HIGH.//
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