Tropical Storm NANGKA Advisory mié, 15-07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 47//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 518 NM SOUTH-
SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED NORTHWARD AT 10 KNOTS OVER
THE PAST SIX HOURS. RECENT ANIMATED MSI DEPICTS A 13 NM DIAMETER EYE
THAT SUPPORTS THE HIGH CONFIDENCE IN THE CURRENT POSITION. THE
INITIAL INTENSITY REMAINS AT 90 KNOTS BASED ON AN OVERALL ASSESSMENT
OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. TY NANGKA
IS LOCATED IN AN AREA OF LOW VWS AND EXCELLENT EQUATORWARD OUTFLOW.
HOWEVER, THERE IS STILL SOME DRY AIR ON THE WESTERN EDGE INHIBITING
THE DEVELOPMENT.  TY 11W IS TRACKING ALONG THE WESTERN PERIPHERY OF
THE DEEP LAYERED SUB-TROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 11W WILL CONTINUE TO TRACK POLEWARD ALONG THE WESTERN
PERIPHERY OF THE STEERING STR IN THE SHORT TERM. AFTERWARD, THIS STR
IS EXPECTED TO REBUILD, FORCING TY NANGKA ON A WEST-NORTHWESTWARD
TRAJECTORY. THE TUTT LOCATED TO THE NORTHEAST  WILL WEAKEN AND TRACK
FURTHER NORTHWARD, SLIGHTLY IMPROVING THE UPPER-LEVEL CONDITIONS.
ALSO, ENVIRONMENTAL CONDITIONS WILL REMAIN, ALLOWING MODEST
INTENSIFICATION OVER THE NEXT 24 HOURS. AS THE SYSTEM GAINS
LATITUDE, DEGRADED CONDITIONS WILL BEGIN TO WEAKEN THE CYCLONE AS IT
APPROACHES AND MAKES LANDFALL OVER THE SOUTHERN COAST OF SHIKOKU.
   C. IN THE EXTENDED TAUS, TY NANGKA WILL TRACK NORTHEASTWARD ALONG
THE THE NORTHWESTERN EDGE OF THE STR. THE COMBINED EFFECTS OF
SIGNIFICANT INCREASING VWS AND COOLER SSTS WILL FURTHER WEAKEN THE
SYSTEM, LEADING TO ITS DISSIPATION BY THE END OF THE FORECAST
PERIOD. AVAILABLE MODEL GUIDANCE IS OVERALL IN FAIR AGREEMENT;
HOWEVER, DUE TO THE CONTINUED SPREAD AND UNCERTAINTY IN THE EXTENT
OF THE STR, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
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