WP, as dry as it's been, my experience is that is will last well into Sept. If rain comes the fish will head upriver. It can be great through the first three weeks, but get there as early in Sept. as you can.
Iv'e been there the 3rd week of September and done great on coho. Nooks not so good. The crowds on labor day were very thin compare to Saturday which was bumper boat city. Fishing had slowed a little on Monday but the remainder of the coho is still a little south of the mouth. 6 miles south of the jetty limits for a party of 8 were had on Pure Gold in 2 hours. Red hot at 12 pulls. That was Monday early morning. Ocean churned up a bit and windy came a visiting.
So, yah, fishing will remain good even after the crowds leave. I hope I get Cindy Lou back soon.