WDPN31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE)
WARNING NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY 
468 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY INDICATES A CONSOLIDATING LOW-LEVEL CIRCULATION 
CENTER (LLCC) WITH FORMATIVE CONVECTIVE BANDING. A 261310Z METOP-B 
89 GHZ IMAGE INDICATES SLIGHT WEAKENING OF DEEP CONVECTIVE BANDING 
DUE TO INTERACTION WITH LAND, AS THE SYSTEM TRACKS OVER MINDANAO, 
HOWEVER, THE INITIAL INTENSITY REMAINS ASSESSED AT 30 KNOTS, HEDGED 
SLIGHTLY HIGHER THAN THE DVORAK ESTIMATES OF 25 KNOTS (T1.5), BASED 
ON A 260027Z ASCAT IMAGE SHOWING 25 TO 30 KNOT WINDS OVER THE 
EASTERN SEMI-CIRCLE. THE INITIAL POSITION IS BASED ON EIR AND THE 
METOP-B IMAGE WITH FAIR CONFIDENCE. THE UPPER-LEVEL ENVIRONMENT IS 
FAVORABLE WITH LOW VERTICAL WIND SHEAR AND GOOD POLEWARD VENTING. TD 
21W IS CURRENTLY TRACKING WESTWARD UNDER THE STEERING INFLUENCE OF 
THE SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC 
REASONING MESSAGE. 
   B. TD 21W IS FORECAST TO CONTINUE TRACKING WESTWARD ALONG THE 
SOUTHERN PERIPHERY OF THE STR, WHICH IS ORIENTED EAST-WEST TO THE 
NORTH. DYNAMIC GUIDANCE IS IN TIGHT AGREEMENT AND REFLECTS A STRONG 
STR THROUGH TAU 72 (AND BEYOND). TD 21W IS FORECAST TO WEAKEN 
SLIGHTLY AS IT TRACKS OVER NORTHERN MINDANAO OVER THE NEXT 12 HOURS, 
HOWEVER, THE SYSTEM SHOULD INTENSIFY AS IT EMERGES OVER THE SULU SEA 
AS IT TRACKS OVER WARM SEA SURFACE TEMPERATURE AND MAINTAINS GOOD 
POLEWARD OUTFLOW. THE GREATEST UNCERTAINTY IS WITH THE INTENSITY 
FORECAST, WHICH IS CONSERVATIVE DUE TO THE IMPENDING LAND 
INTERACTION AND RELATIVELY FAST TRACK SPEEDS, HOWEVER, OVERALL 
CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE AND A HIGHER PEAK 
INTENSITY IS POSSIBLE.
   C. IN THE EXTENDED TAUS, TD 21W IS FORECAST TO MAKE LANDFALL NEAR 
TAU 84, OVER THE EASTERN COAST OF VIETNAM, AND WILL RAPIDLY 
DISSIPATE AS IT TRACKS INLAND. OVERALL, THERE IS HIGH CONFIDENCE IN 
THE JTWC FORECAST TRACK DUE TO THE TIGHT GROUPING OF DYNAMIC AIDS.//
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