Hi clare!
As a rule it doesn't rain alot, remember you're going to the island with the best sushine record in greece. The fact is rain is
more likely late or early in the season. I've seen several Octobers in Rhodes and weather is generally very good, at best i've not seen a cloud in the sky and at worst i've seen flash floods in a week of torrential rain (don't worry that was a one off)!
As the previous post says you can't predict the weather but October is normally fine and sunny. If unlucky, you might get the odd cloudy day and see a little rain.