We were at Typhoon Lagoon last October. It was amazing. The weather when you are going to be there averages a high of 80. I know because it turns out we will be there too at the exact same time, so I have been watching. I think the water is kept at a pleasant temp - not chilly, not warm. In any case, I completely love the disney waterparks. They are now a must do, and a major reason we no longer go to Disneyworld, which would be lots eaiser to do as we live in the west.
One thing I did want to point out, if you go to a water park and a major park (MK EP AK MGM), you will be using two different paid for passes. You cannot "hop" from MK to TL. You use one of your regular day passes for MK and either pay seperately for TL or use one of your "plus" passes, if you purchased these. This isn't a big deal for the day you want to split with DTD, as there isn't any entrance fee, but it just makes for a seriously expensive day if you are going to one of the major parks. Just wanted to make sure you were aware. Besides, I am so taken with the waterparks, I actually don't think it is worth only going for a few hours. You then have to get back to your accomodations, clean up and get to another park, for maybe alot more money. Just my opinion. But relaxing at the water parks is a real treat. Trust me on this one. You will need the break from the chaos of the parks. BTW, I wouldn't say I am a fan of regular water parks at all - I actually pretty much avoid them, but Disney is just different. You'll see.