Feels like autumn here too, and I've seen fallen leaves, but I wouldn't be surprised if we get another hot spell. Dutch weather is unpredictable.
What about another collaborative effort, instead of a contest? We could set up a scene - I don't know, how about a bunch of old friends getting together, in a big rambling old place, for an end-of-summer house party weekend? There's a pool, and a grill, and some comfy spots to lounge alone or together..... There's an eligiac end-of-summer mood, a lot of people who are glad to see each other and a few absent who should have been there.
I figure the writers of The Big Chill got a whole movie out of a similar set-up - we should certainly be able to milk it for a bunch of poems!