WDPN32 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) 
WARNING NR 001//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 21W (TWENTYONE), LOCATED APPROXIMATELY 335 NM 
NORTHWEST OF KOROR, HAS TRACKED NORTHWESTWARD AT 16 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) 
DEPICTS WELL DEFINED BANDING WRAPPING INTO A CONSOLIDATING LOW 
LEVEL CIRCULATION CENTER. THE INITIAL POSITION WAS BASED ON THE PGTW 
FIX WITH FAIR CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 30 
KNOTS, WHICH IS SLIGHTLY HIGHER THAN SUBJECTIVE DVORAK FINAL-T 
ESTIMATES FROM PGTW AND RJTD OF T1.5, BASED ON OVERALL STRUCTURE OF 
THE BANDING. THE UPPER LEVEL ENVIRONMENT IS PROVIDING MODERATELY 
FAVORABLE SUPPORT FOR DEVELOPMENT WITH IMPROVING EQUATORWARD OUTFLOW 
AND LOW 5-10 KNOT VERTICAL WIND SHEAR (VWS). ADDITIONALLY, SEA 
SURFACE TEMPERATURES OF 27-28 DEGREES CELSIUS ARE FAVORABLE. TD 21W 
IS TRACKING GENERALLY NORTHWESTWARD UNDER A SUB-TROPICAL RIDGE TO 
THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST 
PHILOSOPHY.
   B. TD 21W IS EXPECTED TO CONTINUE CONSOLIDATING AS IT TRACKS 
WESTWARD AS FAVORABLE CONDITIONS PERSIST, REACHING 60 KNOTS PRIOR TO 
MAKING LANDFALL OVER THE EASTERN PHILIPPINES NEAR TAU 36. SLIGHT 
WEAKENING IS EXPECTED AS THE SYSTEM TRANSITS OVER THE ARCHIPELAGO, 
BEFORE RE-EMERGING IN THE SOUTH CHINA SEA WHERE RE-INTENSIFICATION 
IS FORECAST TO REACH A PEAK OF 75 KNOTS AT TAU 72. NUMERICAL 
GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 36, BUT BEGINS TO DIVERGE 
AFTERWARDS AS SOME MODELS TRY TO WEAKEN THE STR. THE FORECAST IS 
SLIGHTLY HIGHER THAN THE OFFICIAL CONSENSUS GIVEN CLIMATOLOGICALLY 
FAVORABLE CONDITIONS. HOWEVER, THERE IS LIMITED GUIDANCE FOR THE 
INITIAL FORECAST, LENDING LOW OVERALL CONFIDENCE.
   C. AFTER TAU 72, NUMERICAL GUIDANCE CONTINUES TO DIVERGE AS SOME 
MEMBERS MORE AGGRESSIVELY WEAKEN THE STR. THE OFFICIAL FORECAST IS 
PLACED CLOSE TO THE CONSENSUS MODEL BLEND, WHICH MAINTAINS THE STR, 
WITH WESTWARD TO WEST NORTHWESTWARD MOTION. THE FORECAST INTENSITY 
IS MAINTAINED GIVEN FAVORABLE CONDITIONS OVER THE SCS, UNTIL 
LANDFALL OVER CENTRAL VIETNAM, WHICH OCCURS JUST PRIOR TO TAU 120. 
GIVEN THE LIMITED FIRST WARNING GUIDANCE AND INCREASING MODEL 
SPREAD, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE FORECAST.//
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