Tropical Storm NAMTHEUN Advisory Sa, 03.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 11//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (NAMTHEUN), LOCATED APPROXIMATELY 230 NM SOUTH OF
SASEBO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
SHOWS A WOBBLING COMPACT SYSTEM WITH AN EYE THAT HAS BECOME
CLOUD-FILLED AS CENTRAL CONVECTION BECAME MORE SHALLOW. THE INITIAL
POSITION IS BASED ON THE EIR LOOP AND COMPOSITE RADAR REFLECTIVITY
LOOP FROM THE JAPAN METEOROLOGICAL AGENCY WITH FAIR CONFIDENCE. THE
INITIAL INTENSITY OF 90 KNOTS IS BASED ON A RJTD AND OBJECTIVE DVORAK
ESTIMATES OF T5.0. FAVORABLE ENVIRONMENTAL CONDITIONS WITH SSTS NEAR
29C, HIGH OCEAN HEAT CONTENT, AND STRONG POLEWARD OUTFLOW ARE BEING
OFFSET BY STRONG (25-30 KNOTS) 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 NORTH-NORTHWESTWARD
ALONG THE WESTERN PERIPHERY OF THE STR MAKING LANDFALL ALONG THE
WESTERN COAST OF KYUSHU 40 NM SOUTH OF SASEBO JUST AFTER TAU 36.
AFTERWARD, THE SYSTEM WILL TURN NORTHEASTWARD AS IT ROUNDS THE STR
AXIS, WITH CLOSEST POINT OF APPROACH TO SASEBO AT APPROXIMATELY 10 NM
TO THE EAST. INCREASING VWS THEN LAND INTERACTION WILL GRADUALLY
WEAKEN THE SYSTEM, HOWEVER, IT WILL STILL BE AT TYPHOON INTENSITY AT
TAU 36 AS IT MAKES LANDFALL. 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 48, 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 REMAINS IN TIGHT AGREEMENT. THE JTWC TRACK FORECAST IS LAID
SLIGHTLY TO THE EAST OF CONSENSUS TO OFFSET A LESS LIKELY WIDE
WESTWARD TURN PROPOSED BY EGRR. THE OVERALL CONFIDENCE IN THE JTWC
TRACK FORECAST IS DOWNGRADED TO FAIR DUE TO THE TROCHOIDAL (WOBBLING)
STORM MOTION.//
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