Stupid seasonal produce!
Of course, this means there's an equivalent worst day: when end-of-summer denial is no longer sufficient insulation, and the t-shirts are regretfully put into storage again and replaced with heavy coats and waterproof boots and flannel pajamas.
I have a parallel experience in the grocery store. There's the day when the produce section is miraculously overflowing with local tomatoes and corn and peaches and berries. And then, for no good reason, they take it all away and replace it with a solid, mocking wall:
Not that I have anything against pumpkins, per se. It's just that they signify the inevitable return of winter. They mean waving goodbye to fresh raspberries and plums and nectarines, and instead relying on carrots and beets and yams. They say, "Oh, you want fruit? Sure, there's fruit—as long as you like apples! And how, exactly, do you like them apples, huh?"
There are survival strategies, of course. One of mine is to turn late-season fruit—such as the New Jersey peaches I picked up this weekend—into crumbles and keep them in the freezer. They'll stay there until a particularly gray and miserable winter night.
In case of emergency, preheat oven to 350.