I agree with others, it will rain, it will be hot and muggy after it rains, parks will sort of clear out when it's raining. Hydrate, hydrate, hydrate.
If you are a planner, make plans to go back to the resort to either rest, change clothes or swim. If you aren't a planner, try to go back to the resort to either rest, change clothes or swim. I'm from Georgia and the heat and humidity don't really bother us but we almost always go for a swim mid-day.
Speaking of rain, I take different levels of rain gear. If it looks like it just might be a light rain or drizell, I carry a throw away poncho. If it looks like it might rain on and off all day, I carry a rain jacket that goes all the way to the ground. If it looks like it might have quick but heavy showers, I carry a heavier poncho. If the forecast says its not going to rain at all, I carry a small umbrella cause it's going to rain and umbrellas are also great to keep the sun off you. No matter what I always have a throw away poncho with me even if I don't have an umbrella, heavy poncho or rain jacket, just in case.
Breaks are your friend, find somewhere to sit and have something to drink or just to sit and relax.