WDPN32 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (CHOI-WAN) WARNING 
NR 13//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (CHOI-WAN), LOCATED APPROXIMATELY 669 NM
NORTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED WEST-NORTHWESTWARD 
AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY DEPICTS A DEEPENING IN THE CURVED BANDING ALONG 
THE SOUTHERN PERIPHERY AND WRAPPING INTO THE LOW LEVEL CIRCULATION 
CENTER (LLCC). A 051102Z AMSU-B MICROWAVE IMAGE SHOWS WELL DEFINED 
SPIRAL BANDING WRAPPING INTO A BETTER CONSOLIDATED LLCC. THE CURRENT 
POSITION IS BASED ON THE LLCC IN THE ABOVE IMAGERY WITH GOOD 
CONFIDENCE AND IS SUPPORTED BY SATELLITE FIXES FROM RJTD AND PGTW. 
THE INITIAL INTENSITY IS HELD AT 60 KNOTS BASED ON AN ASSESSMENT OF 
DVORAK INTENSITY ESTIMATES OF T3.5 (55 KNOTS) FROM ALL AGENCIES AND 
THE CONTINUED IMPROVEMENT IN THE OVERALL SYSTEM STRUCTURE. UPPER-
LEVEL ANALYSIS CONTINUES TO SHOW A FAVORABLE ENVIRONMENT WITH RADIAL 
OUTFLOW 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 CHOI-WAN WILL BEGIN TO ROUND THE SOUTHWESTERN PERIPHERY OF 
THE STEERING STR AND TRACK ON A POLEWARD TRAJECTORY. FAVORABLE 
ENVIRONMENTAL CONDITIONS WILL PERSIST FOR THE NEXT 36 HOURS, 
ALLOWING TS 23W TO REACH A PEAK INTENSITY OF 85 KNOTS BEFORE MOVING 
INTO AN UNFAVORABLE ENVIRONMENT. BEYOND TAU 36, THE STORM WILL BEGIN 
TO INTERACT WITH THE BAROCLINIC ZONE WHERE VWS WILL INCREASE ABOVE 
30 KNOTS. IN ADDITION, SSTS WILL DROP BELOW 26 CELSIUS, FURTHER 
WEAKENING THE CYCLONE. NEAR TAU 48, TS CHOI-WAN WILL BECOME ENGULFED 
BY A MID-LATITUDE TROUGH WHICH WILL FURTHER INCREASE THE VWS AND 
BEGIN EXTRA-TROPICAL TRANSITION (ETT). TS CHOI-WAN WILL GAIN FRONTAL 
CHARACTERISTICS AND COMPLETE ETT BY THE END OF THE FORECAST PERIOD 
AS A STRONG COLD-CORE LOW. DYNAMIC MODEL GUIDANCE REMAINS IN VERY 
TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD, LENDING TO HIGH 
CONFIDENCE IN THE JTWC TRACK FORECAST.//
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