Tropical Storm CHOI-WAN Advisory 04.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (CHOI-WAN) WARNING
NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (CHOI-WAN), LOCATED APPROXIMATELY 905 NM
EAST-NORTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED WEST-NORTHWESTWARD
AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) SHOWS A BETTER CONSOLIDATED STORM WITH
INCREASED CONVECTION WRAPPING TOWARDS THE CENTER; HOWEVER, IT IS
STILL DEVOID OF CENTRAL CONVECTION LEAVING A LARGE EXPOSED CENTER.
THE BULK OF DEEP CONVECTION IS ALONG THE NORTHWESTERN AND
SOUTHEASTERN PERIPHERIES. THE INITIAL POSITION IS BASED ON THE
CENTER OF THE CENTROID IN THE MSI IMAGERY AND SUPPORTED BY SATELLITE
FIXES FROM RJTD AND PGTW WITH FAIR CONFIDENCE. THE INITIAL INTENSITY
IS HELD AT 50 KNOTS BASED ON A RECENT SATCON INTENSITY ESTIMATE OF
52 KNOTS AND A DVORAK INTENSITY ESTIMATE OF T3.0 (45 KNOTS) FROM
RJTD. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH
RADIAL OUTFLOW, DUE TO A POINT SOURCE, AND LOW VERTICAL WIND SHEAR
(VWS). ADDITIONALLY, WARM SEA SURFACE TEMPERATURES (SSTS) ARE
CONDUCIVE FOR FURTHER DEVELOPMENT. TS 23W IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE
NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 23W WILL CONTINUE TRACKING WESTWARD UNDER THE INFLUENCE OF
THE STR OVER THE NEXT 36 HOURS. FAVORABLE ENVIRONMENTAL CONDITIONS
WILL PERSIST; HOWEVER, DUE TO THE BROAD NATURE OF THE SYSTEM, TS 23W
IS EXPECTED TO GRADUALLY INTENSIFY AS IT CONTINUES TO CONSOLIDATE.
AFTERWARDS, TS CHOI-WAN IS FORECAST TO ROUND THE STR AND TRACK MORE
POLEWARD. AS THE SYSTEM GAINS LATITUDE, IT WILL ENCOUNTER INCREASING
VWS AND DECREASING SSTS WHICH WILL BEGIN TO WEAKEN THE SYSTEM.
   C. BEYOND TAU 72, VWS WILL RAPIDLY INCREASE ABOVE 30 KNOTS AND
SSTS WILL DROP BELOW 26 CELSIUS WHICH WILL INCREASE THE RATE OF
WEAKENING. TS CHOI-WAN WILL BEGIN TO INTERACT WITH THE BAROCLINIC
ZONE NEAR TAU 72 WHICH WILL BEGIN EXTRA-TROPICAL TRANSITION. BY TAU
96, TS 23W WILL BE FULLY EMBEDDED IN THE BAROCLINIC ZONE, GAINING
FRONTAL CHARACTERISTICS, AND TRANSITIONING TO A STRONG COLD-CORE
LOW. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT; HOWEVER,
GIVEN THE UNCERTAINTY IN THE INITIAL POSITION AND, THEREFORE, THE
CURRENT STORM MOTION, THERE IS STILL LOW CONFIDENCE IN THE JTWC
FORECAST TRACK.//
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