Rain does put a damper on the day but the good thing about galveston is that they only shut down in lightning...the park was designed to provide covering when needed in light rain, cold and other weather. It was the one of the first waterparks to build retractable awnings that span across the top of the lazy river as well as some rides and the interior of the park where the kids area is....Even with this feature nothing beats a sunny hot day at the water park though!
I lived down there for the past 5 years and had a season pass last season and loved every day i went.