Tropical Storm NAMTHEUN Advisory Sun Sep 04

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (NAMTHEUN) WARNING
NR 17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (NAMTHEUN), LOCATED APPROXIMATELY 24 NM
SOUTH OF SASEBO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY AND THE KYUSHU RADAR LOOP SHOW THAT THE REMAINING
SIGNIFICANT CONVECTION ASSOCIATED WITH THE SYSTEM IS MAKING LANDFALL
NEAR NAGASAKI, JAPAN. THE LOW LEVEL CIRCULATION CENTER (LLCC) IS
POSITIONED WITH FAIR CONFIDENCE JUST OFF-SHORE BASED ON THE
BROADENING LLCC IN THE RADAR LOOP AND A SATELLITE FIX FROM PGTW. THE
CURRENT INTENSITY IS 50 KNOTS BASED ON AN AVERAGE OF CURRENT
INTENSITY ESTIMATES RANGING FROM 45 TO 55 KNOTS AND SUPPORTS THE
CONTINUED WEAKENING OF THE CONVECTIVE STRUCTURE. ENVIRONMENTAL
CONDITIONS REMAIN UNFAVORABLE DUE TO HIGH (30-35 KNOT) VERTICAL WIND
SHEAR (VWS) AND INCREASED LAND INTERACTION; HOWEVER, THE STRONG
POLEWARD OUTFLOW AS SEEN IN WATER VAPOR IMAGERY IS PROVIDING AN
EXHAUST FOR THE CURRENT CONVECTION. TS NAMTHEUN HAS MOVED NORTH OF
THE SUB-TROPICAL RIDGE (STR) AXIS AND IS BEGINNING TO TURN
NORTHEASTWARD.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS NAMTHEUN WILL CONTINUE TO TRACK NORTHEASTWARD AND CROSS
KYUSHU OVER THE NEXT 6 HOURS. AFTERWARDS THE STORM WILL EMERGE OVER
THE SEA OF JAPAN (SOJ) AND ACCELERATE NORTHEASTWARD WITH THE MID-
LATITUDE WESTERLY FLOW WHERE IT WILL CONTINUE TO WEAKEN DUE TO COLD
WATER (LESS THAN 25C) AND INCREASING VWS. TS 15W WILL BEGIN EXTRA-
TROPICAL TRANSITION (ETT) NEAR TAU 24 AND COMPLETE ETT AS A WEAK
COLD-CORE LOW BY TAU 36. THERE IS A DISTINCT POSSIBILITY THAT THE
SYSTEM WILL DISSIPATE IN THE SOJ DURING ETT. DYNAMIC MODEL GUIDANCE
IS IN TIGHT AGREEMENT, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK.//
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