WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) 
WARNING NR 06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY 
260 NM SOUTH OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 11 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE 
IMAGERY CONTINUES TO DEPICT WEAKENED DEEP CONVECTION AS THE SYSTEM TRACKS 
ACROSS THE PHILIPPINE ISLANDS. A 271130Z SSMIS MICROWAVE IMAGE REVEALS 
BROKEN CONVECTIVE BANDING LOOSELY WRAPPING INTO THE CENTER. THE CURRENT 
POSITION IS BASED ON THE EIR ANIMATION, PGTW SATELLITE FIX AND SSMIS IMAGE
WITH FAIR CONFIDENCE. THE INITIAL INTENSITY REMAINS AT 30 KNOTS BASED ON 
DVORAK INTENSITY ESTIMATES FROM PGTW AND KNES AND CURRENT STRUCTURE. 
UPPER-LEVEL ANALYSIS INDICATES TD 21W IS NOW LOCATED IN AN AREA OF LOW
TO MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR OFFSET BY EXCELLENT
POLEWAR OUTFLOW, AS EVIDENT IN THE WATER VAPOR IMAGERY. TD 21W 
IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A 
SUBTROPICAL RIDGE (STR) ANCHORED TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC 
REASONING MESSAGE.
   B. TD 21W WILL CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE STEERING
INFLUENCE OF THE STR. FAVORABLE CONDITIONS IS EXPECTED TO PERSIST ALLOWING 
TD 21W TO GRADUALLY INTENSIFY AS IT TRACKS INTO THE SOUTH CHINA SEA. THE
SYSTEM IS FORECAST TO MAKE LANDFALL ACROSS THE EASTERN COAST OF VIETNAM 
AND WILL RAPIDLY DISSIPATE AS IT TRACKS INLAND. AVAILABLE MODEL GUIDANCE 
REMAINS IN GOOD AGREEMENT, LEADING HIGH CONFIDENCE IN THE JTWC FORECAST 
TRACK WHICH IS POSITIONED CLOSE TO MULTI-MODEL CONSENSUS.//
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