Don't pay attention the forecast summary, read the details. I spent almost the entire weekend outside in Seattle (half of it on the water) and spent less than an hour total in the rain. Bring good clothes and enjoy the great scenery and sailing.
Also realize that most weather forecasts draw a rain symbol if there is a 30% chance of rain. There is always a 30% chance of rain here at this time of year, but that still means that 70% of the time it's not raining. Today was sunny until about 3pm. Last night at sunset I took this photo just outside of Shilshole marina:
The wind was weird this weekend. Both yesterday and today it switched between periods of being 5mph and 25mph and also kept switching between a northerly and a southerly.