Tropical Storm SEPAT Advisory Çar, 02.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (SEPAT) WARNING NR
08//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 21W (SEPAT), LOCATED APPROXIMATELY 178 NM SOUTH-
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 14 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
(EIR) SHOWS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
THAT HAS BEGUN TO ELONGATE AS IT MAINTAINED SHALLOW CONVECTION
WRAPPING ALONG THE NORTHERN SEMI-CIRCLE. THERE IS FAIR CONFIDENCE IN
THE INITIAL POSITION BASED ON THE PARTIALLY EXPOSED NATURE OF THE
LLCC. THE INITIAL INTENSITY OF AT 35 KNOTS BASED ON DVORAK INTENSITY
ESTIMATES FROM PGTW, RJTD AND KNES. UPPER-LEVEL ANALYSIS INDICATES
STRONG POLEWARD OUTFLOW WHICH IS BEING OFFSET BY HIGH (25-40 KNOTS)
VERTICAL WIND SHEAR (VWS). TS 21W IS BEGINNING TO TRACK POLEWARD
ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 21W HAS STARTED TO RECURVE AS IT BEGINS TO CREST THE STR
AXIS. AFTER TAU 12, THE SYSTEM IS FORECAST TO BEGIN TO ACCELERATE
AHEAD OF THE DIGGING MIDLATITUDE SHORTWAVE TROUGH, WHICH IS EXPECTED
TO FURTHER DEEPEN OVER JAPAN. TS 21W IS FORECAST TO REMAIN IN A
MARGINAL ENVIRONMENT THROUGHOUT THE FORECAST AND WILL STRUGGLE TO
MAINTAIN TROPICAL STORM STRENGTH AS THE INCREASING POLEWARD OUTFLOW
CONTINUES TO BE OFFSET BY FURTHER INCREASING VWS. ADDITIONALLY,
ALONG-TRACK SEA SURFACE TEMPERATURES ARE DECREASING WHICH WILL ALSO
IMPEDE DEVELOPMENT. TS 21W HAS BEGUN EXTRA-TROPICAL TRANSITION (ETT)
AND COMPLETE TRANSITION IS EXPECTED BY TAU 12 AS THE SYSTEM BECOMES
EMBEDDED IN THE COLD BAROCLINIC AIR MASS. THE AVAILABLE DYNAMIC
MODELS, AS WELL AS THE ENSEMBLE MODELS ARE IN EXCELLENT AGREEMENT,
LENDING TO HIGH CONFIDENCE TO THE JTWC FORECAST TRACK, WHICH IS
POSITIONED SLIGHTLY FASTER AND TO THE RIGHT OF THE MULTI-MODEL
CONSENSUS.   //
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