Half marathon is Labor Day weekend.
Other than that, I can't think of anything that was going on on our last Sept trip, but I'm going then, too, and would love to know!
I'm hoping, but am not counting, on Tarzan being open again by then. I liked being up in that tree.
Someone told me that Sept is some sort of traditional time for Matterhorn to be closed for maintenance. I looked on whichever website it is that shows that sort of thing, and verified that it was closed last year for big maintenance, and the year before that for something, and I *think* the year before for something else, but it didn't seem to be a single common trend, just a few years for somewhat different reasons. I really really HOPE that the expert was wrong, but since I see very accurate reports from the person elsewhere (I can't remember who it was, though) I'm thinking they know better than I do. So I'm gearing myself for NO Matterhorn.
But you're asking about events, and I guess that other than knowing when the marathon will be, I don't have much info!