I think so. Not just this one either. Apparently there are three legendary beasts here and they all have some control over weather events.

[Or, well, that is what his voltorb's picture book claims. It might not be the most scientific source.]

No clue. I've asked a few people who've been here for a very long time, and they've never seen anything like this. Legendaries have been active before, but that was usually when Team Rocket was involved and there has been no sign of them this time.