We went in February a couple of years ago. We all came back with a great tan and the sun shone every day. You will need sun tan lotion.
The waterparks were quite chilly in the mornings, probably a bit too cold, but being Brits we tend to gin and bear it. When the sun comes out in the afternoon it's like British summertime heat. No rain to speak of for the entire two weeks, however if the wind gets up it can be cold.
The queues were virtually non existant apart from Magic Kingdom. Seaworld and Busch gardens were especially quiet, we were the only ones on Kraken at midday !! Everything is open as usual but one of the disney waterparks closes for routine maintenance - so check which one is closed before buying tickets.
Watch out for Spring break weekend or presidents day which I think is around this time as the parks suddenly get manic.