Old rule of thumb is no matter what a Chinook will make Schaffer Park by October 10th, always. Rain will move them out of the Chehalis or above South Elma but not above Porter in any numbers before a major brown out in the latter part of October. Tangle netting for broodstocking it was two or three a night, little rain maybe more. Brown out full blown stampede.

Satsop kinda the same but the water rise early ( or very early ) gets them into the West, Middle, & East Forks but not much farther. To early for them to spawn so they move which puts them above the fishing cut off lines but they have to stage waiting to spawn and that is a time driven thing.

I want to agree with you but a August or early Sepember rain is way different than a early October rain event. Odds are it will only draw them out of the bay into upper tidewater and lower parts of the tribs. They will slowly work their way upstream depending on timing and conditions.

Early rain depending on how much can cause Coho to do early movements way off normal which is why inriver fisheries like early rain and brown outs are best as brings them in and on the drop they slow down and stop.

Then you have a year like last year that is an outlier which frankly falls in the fish will screw you everytime! As the saying goes fish do what fish do not necessarily what we fishers would like them to do.