I am from Oregon which is supposed to have similar weather, 27 rainy days in June!
We do not get heavy downpours much, just a drizzly, misty sort of thing. I think I would hesitate in a heavy rain but the misty stuff is no problem, just make sure to dry everything carefully when you go back in.
And keep in mind that weather sealed or not the lens will draw in air and then back out on every zoom, so the air inside the lens will be very humid. No problem, unless you go into a cold place (air conditioning) in which case it is possible to get condensation on the inside. This is not likely but it can happen. I had the reverse happen to me in Cartagena, Columbia. After spending some time in very air conditioned building I went outside to normal (105 F and 100% humidity) and my DA*16-50 immediately fogged up and I could take a picture for almost 20 minutes until it warmed up to ambient temperature.
WR does not mean invincible just protected, and if you are out in the weather you need to take due care of your gear when you go back in but a normal drizzle is just fine.