We go in Value season, when it's less crowded. January & late August.
January, weather is unpredictable. It can be quite pleasant with temps in 70s or low 80s or you can get a cold snap with freezing temps or a combination of the 2. While still relatively low crowds, I've noticed the parks aren't as empty as they once were.
Late August, it's hot & humid. Predictable short 3 pm showers or T storms. Usually last 30 min tops. The heat doesn't bother us, but if you are heat intolerant it's not the time to go. The closer to Sept you get, the lower the crowds. The southern schools are back in session.
We enjoy taking mid day breaks back at our resort pool during the hottest time of day.