Twice, I went outside to make sure that's what I was hearing, rather than an ambulance, say. I checked the weather report: no word about high seas here. And then, the siren turned to some kind of talking which, unlike the siren, is absolutely not capable of being understood this far away.
So, I turned to the Google, asking for "Washington Tsunami Warning" and was answered by:
Millions of people worldwide will practice how to
Drop, Cover, and Hold On at 10:20 a.m. on October 20* during Great ShakeOut Earthquake Drills!