Kokua Line: Why was warning siren going off in East Oahu?

Question: Is anybody else asking about a very loud pulsating noise near Queen’s Gate? This continued on-and-off from Wednesday night into early Thursday. At first I thought it was an extra loud car alarm but I don’t think it was. Late Wednesday night, I walked down to Kalama Valley Community Park thinking it could be the emergency siren there, but it wasn’t. Thursday morning I checked Oahu’s emergency siren map and the two other closest sirens are listed as working so I don’t think it was them. I am wondering what it was, what it meant and whether it is going to happen again?