Tropical Storm NAMTHEUN Advisory Mon Sep 05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (NAMTHEUN) WARNING
NR 16//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (NAMTHEUN), LOCATED APPROXIMATELY 67 NM
SOUTH OF SASEBO, JAPAN, HAS TRACKED NORTHWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS
DIMINISHING CONVECTION WITH WARMING CLOUD TOPS AND AN ELONGATED
STRUCTURE DUE TO PERSISTENT HIGH (30-35 KNOT) SOUTHWESTERLY VERTICAL
WIND SHEAR (VWS). A 040545Z AMSU 89GHZ MICROWAVE IMAGE AND THE
KYUSHU RADAR LOOP SHOW A DEFINED LOW LEVEL CIRCULATION CENTER STILL
EVIDENT WHICH SUPPORTS THE CURRENT POSITION WITH GOOD CONFIDENCE.
THE INTENSITY HAS BEEN DECREASED TO 55 KNOTS DUE TO CONSENSUS DVORAK
CURRENT INTENSITY ESTIMATES OF T3.5 (55 KNOTS) FROM PGTW AND RJTD.
THE CURRENT AND FORECASTED WIND RADII HAVE BEEN DECREASED BASED ON A
040154Z PARTIAL ASCAT PASS SHOWING THE NORTHERN AND WESTERN
QUADRANTS. THE AFOREMENTIONED VWS AND INCREASED LAND INTERACTION IS
RESPONSIBLE FOR THE STRUGGLING CONVECTIVE STRUCTURE; HOWEVER, THE
STRONG POLEWARD OUTFLOW AS SEEN IN WATER VAPOR IMAGERY IS PROVIDING
AN EXHAUST FOR THE CURRENT CONVECTION. 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 NAMTHEUN IS FORECAST TO CONTINUE TRACKING NORTHWARD ALONG
THE WESTERN PERIPHERY OF THE STR AND WEAKEN AS IT GAINS LATITUDE DUE
TO INCREASING VWS AND LAND INTERACTION. TY 15W WILL MAKE LANDFALL
ALONG THE WESTERN COAST OF KYUSHU, JUST SOUTH OF SASEBO, NEAR
041400Z. AFTERWARDS THE SYSTEM WILL ROUND THE STR AXIS AND
ACCELERATE NORTHEASTWARD WITH THE MID-LATITUDE WESTERLY FLOW. RAPID
DECAY WILL CONTINUE AS THE CYCLONE MOVES OVER COLD WATER (LESS THAN
25C) IN THE SEA OF JAPAN (SOJ). TY 15W WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT) NEAR TAU 24 AND COMPLETE ETT AS A WEAK COLD-CORE
LOW BY TAU 48. THERE IS A DISTINCT POSSIBILITY THAT THE SYSTEM WILL
DISSIPATE IN THE SOJ DURING ETT. DYNAMIC MODEL GUIDANCE REMAINS IN
TIGHT AGREEMENT, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.
THERE IS A 40NM SPREAD IN MODEL SOLUTIONS AS TY NAMTHEUN MAKES
LANDFALL OVER KYUSHU.//
NNNN
NNNN