Now that I'm on my computer instead of cell...
During our Feb cruise, the water at Castaway actually *felt* warmer to me than the water the next October. I think it's a relative warmth thing. It was in the 70s in Feb, but higher 80s in October, and the water wasn't that much different. So the water felt colder compared to how warm my skin was in October.
But it's absolutely hit or miss.
We are now so tired of the weather in FL in January that I can't see going to WDW again during that month. It's been too cold too often during our January trips and I can't take it anymore. For whatever reason, I get sick and STAY sick, and two Januarys in a row I've ended up sick for well over a month and beyond, after a cold January trip. Whereas others go in weeks when we aren't there in January and don't experience freezing cold days at all!