WDPN31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (JEBI) WARNING NR 
05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 09W (JEBI), LOCATED APPROXIMATELY 567 NM
SOUTHEASTWARD OF HANOI, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD
AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) DEPICTS A MONSOON DEPRESSION WITH THE BULK 
OF THE DEEP CONVECTION AND STRONGER WINDS DISPLACED OVER THE 
PERIPHERY. MSI DEPICTS TWO DISTINCT CIRCULATIONS WITH THE PRIMARY 
LOW-LEVEL CIRCULATION CENTER (LLCC) LOCATED NEAR 15.5N 114.0E AND A 
SMALL, EXPOSED CIRCULATION NEAR 15.8N 114.7E. THE CURRENT POSITION 
IS BASED ON THE PRIMARY, DOMINANT LLCC, WHICH IS POSITIONED OVER THE 
WESTERN SEMI-CIRCLE OF THE MONSOON DEPRESSION WITH CONVECTIVE 
BANDING WRAPPING INTO A WELL-DEFINED LLCC. THERE IS FAIR CONFIDENCE 
IN THE INITIAL POSITION DUE TO THE MULTIPLE CIRCULATIONS. THE 
INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON A DVORAK ESTIMATE 
OF 35 KNOTS FROM KNES AND RECENT SCATTEROMETER DATA. UPPER-LEVEL 
ANALYSIS REVEALS A FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW (05-10 
KNOTS) VERTICAL WIND SHEAR AND FAVORABLE OUTFLOW THAT IS ENHANCED BY 
A TUTT CELL LOCATED NORTH OF TAIWAN. TS 09W IS MOVING SLOWLY 
WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED 
SUBTROPICAL STEERING RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 09W IS EXPECTED TO TRACK NORTHWESTWARD THROUGH TAU 24 ALONG 
THE SOUTHERN PERIPHERY OF THE STR IN RESPONSE TO AN APPROACHING 
MIDLATITUDE SHORTWAVE TROUGH, WHICH IS FORECAST TO WEAKEN THE 
WESTERN PERIPHERY OF THE STR. AFTER TAU 24, THE STEERING RIDGE IS 
EXPECTED TO RE-BUILD OVER CHINA PRODUCING A MORE WEST-NORTHWESTWARD 
TRACK WITH FASTER TRACK SPEEDS. DYNAMIC GUIDANCE REMAINS IN TIGHT 
AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST 
TRACK. TS 09W IS FORECAST TO SLOWLY INTENSIFY TO A PEAK INTENSITY OF 
50 KNOTS PRIOR TO TRACKING OVER HAINAN ISLAND. ALTHOUGH 
ENVIRONMENTAL CONDITIONS ARE FAVORABLE, THE BROAD, MONSOON 
DEPRESSION-LIKE NATURE OF THE LLCC IS EXPECTED TO SLOW DEVELOPMENT. 
BY TAU 36, THE SYSTEM WILL BEGIN INTERACTING WITH LAND AND WILL 
WEAKEN SLIGHTLY THEN RE-EMERGE OVER THE GULF OF TONKIN AFTER TAU 42. 
TS 09W WILL MAKE LANDFALL OVER NORTHERN VIETNAM AFTER TAU 48 AND 
WILL WEAKEN RAPIDLY DUE TO INCREASED FRICTION ASSOCIATED WITH LAND 
INTERACTION.   
   C. IN THE EXTENDED TAUS, TS 09W WILL TRACK ALONG THE SOUTHWEST 
PERIPHERY OF THE STR AND WILL DISSIPATE BY TAU 96.//
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