subj/prognostic reasoning for typhoon 21w warning nr 16//
rmks/
1. For meteorologists.
2. 12 hour summary and analysis.
   A. Typhoon (TY) 21w (peipah) reached peak intensity and began
to weaken slightly over the past 12 hours. Animated multispectral
imagery, and a 062247z image, show the system tracking southwestward.
Forward speed is slow as the storm remains in a relatively weak stee-
ring environment.
   B. The current storm intensity is based on the available dvorak
satellite intensity estimates that range from 65 to 77 knots. Current
upper level analysis depicts an anticyclone over the center. Poleward
outflow remains favorable, though convection has decreased significa-
ntly over the past 12 hours. Upper-level convergence south of the sys-
tem continues to hinder the equatorward outflow.  
3. Forecast reasoning.
   A. The forecast philosophy remains the same as the previous
prognostic reasoning.
   B. TY 21w is tracking along the southeastern periphery of a devel-
oping mid-level subtropical ridge to the north. This mid-level ridge 
will continue to build north of the system, and provide a stronger
steering influence after tau 12. As the ridge builds to the north, the
system will track generally southwestward at an increased rate of for-
Ward speed. Poleward outflow will continue to decrease as the ridge
builds. This decrease in poleward outflow and increasingly marginal
ocean heat content, will lead to a weakening of the system throughout
the forecast period.
   C. TY 21w will continue tracking along the southern periphery of
the steering ridge and weaken during the extended Taus. Dissipation 
shortly after landfall in southeastern Vietnam is expected near tau
96.
Forecast team: Charlie//