WDPN32 PGTW 250300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (HAITANG) 
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL DEPRESSION (TD) 21W (HAITANG), LOCATED APPROXIMATELY 
325 NM EAST OF HUE, VIETNAM, HAS TRACKED NORTH-NORTHEASTWARD AT 07 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY REVEALS A BROAD, NEARLY FULLY EXPOSED LOW LEVEL CIRCULATION 
CENTER(LLCC). SATELLITE ANIMATION ALSO SHOWS THAT TD 21W IS 
BEGINNING TO CURVE POLEWARD INTO AN ANTICIPATED WESTWARD LEG. THE 
CURRENT INTENSITY IS BASED ON A SHIP REPORT OF 30 KNOTS IN THE 
CONVERGENT WESTERLIES 50 NM SOUTH OF THE LLCC AND AN AVERAGE OF 
DVORAK ESTIMATES FROM RJTD AND KNES. A 242257Z SSMIS IMAGE DEPICTS 
CURVED CONVECTIVE BANDING ORGANIZING AROUND THE LLCC BUT LITTLE DEEP 
CONVECTION. ANIMATED WATER VAPOR IMAGERY REVEALS EXCELLENT 
EQUATORWARD OUTFLOW. THE 241200Z PGTW UPPER LEVEL STREAMLINE 
ANALYSIS DEPICTS AN ANTICYCLONE BETWEEN TAIWAN AND LUZON, WHICH IS 
PRODUCING 15-20 KNOTS OF VERTICAL WIND SHEAR OVER THE SYSTEM. THE 
SHEAR IS BEING COMPENSATED SOMEWHAT BY THE HIGHLY DIFFLUENT FLOW 
ASSOCIATED WITH THE SOUTHWEST QUADRANT OF THE ANTICYCLONE. SEA 
SURFACE TEMPERATURE IS 31 DEGREES. TD 21W ORIGINATED IN THE MONSOON 
TROUGH AND IS SITUATED WITHIN A WEAK STEERING ENVIRONMENT. 
3. FORECAST REASONING. 
    A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY.
    B. TD 21W IS SITUATED WITHIN A WEAK STEERING ENVIRONMENT AND IS 
EXPECTED TO DRIFT EASTWARD TO NORTHEASTWARD IN THE NEAR TERM BUT 
SHOULD BEGIN TO TRACK WESTWARD AFTER TAU 12 AS THE LOW-LEVEL 
SUBTROPICAL RIDGE RE-BUILDS OVER EASTERN CHINA. TD 21W WILL REMAIN 
WITHIN A MARGINAL ENVIRONMENT WITH MODERATE VERTICAL WIND SHEAR AND 
BROAD DIFFLUENCE, AND IS EXPECTED TO REMAIN AT TD OR WEAK TROPICAL 
STORM STRENGTH UNTIL IT MAKES LANDFALL OVER THE VIETNAMESE COAST 
NEAR TAU 60.//
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