Has anyone been in Mykonos, Santorini, or Ios in late Sept and early (the first week of) October?

What was the weather like? Was the ocean warm enough to swim in (comfortably)? Was it warm enough to lay out on the beach?

Also, I know the party season has winded down by then, but are there still places to go out at night? Or is everything deserted?

I'm going on the Greek Island hopping in the last week of Sept / early Oct, and want to get a sense of what the weather will be like.

thanks!