Grays Harbor Tourism has a comprehensive event search function on their website:
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Grays Harbor is mostly focused on the Ocean Beaches - Westport, Grayland, Tokeland to the South, and Ocean Shores to the North.
In Westport:
You just missed the Annual Crab Races, which was in Mid-April.
This weekend is the Cleanwater Classic & Surf Festival (May 15 - 17)
Rusty Scuppers Pirate Daze kind of kicks off the touristy season on June 26-28th.
Fourth of July will have festivals in most of these small towns.
Westport hosts a great Art Festival August 15 - 16.
Seafood Festival is Labor Day weekend.
Crush Me, Squeeze me, Make me wine at the beach (wine festival) in October.
Wine & Chocolate festival in the north beach in early spring is a lot of fun too!
Enjoy!