My apologies as I'm sure I'm repeating some of what others have said, but here are my tips after our trip in late August 2021 (which we enjoyed so much, regardless of the weather, that we're going again in August 2023!):
- PONCHOS. While flimsy disposables are great for the rest of the year, during hurricane season, you run the risk that a rainy downpour will be accompanied by high winds, which can tear the flimsy ones right off of you and turn umbrellas inside out, and at the very least, won't allow you to keep your hood up. If you're bringing ponchos for rain and not just for Kali River Rapids or Splash Mountain, invest in some breathable, higher-quality ponchos with a drawstring hood (e.g., Frog Toggs or similar), that are designed to fold easily into a pouch or their own pocket.
- FOOTWEAR. Make sure everyone has a pair of waterproof hiking sandals or other waterproof footwear that can dry quickly, AND does not get slippery when wet. (Many shoes have marshmallowy rubber substitutes on the soles that do not have good traction in wet conditions.)
- CLOTHING. It's all about fabric choices. Wear moisture-wicking, lightweight clothing (like that designed for golfers, fisherman, and tennis players) that will dry quickly and won't chafe when wet. Bonus: those silky, feather-weight fabrics don't wrinkle, and pack like a dream! Bring an extra shirt for every outfit, so you can freshen up and put on a clean one for your afternoon touring.
- ELECTRONICS PROTECTION/PARK BAG. Bring something (e.g., a small lightweight, breathable backpack, like the Eddie Bauer 20L Stowaway or similar) that is small enough for you to wear under your poncho if it rains. Avoid bringing a park bag that is too big and heavy to fit under the poncho, or made of leather or vinyl: you'll be hot and sticky, and a giant lump of non-breathable material against your body is the last thing you'll want.
- CONSIDER COOLING TOWELS. Granted, I bought them for the whole family, and I was the only one who ended up using mine as intended (dampened, and worn around my neck to cool me down as the moisture evaporated). However, they also turned out to be really handy, when dry, for wiping down wet outdoor benches or ride seats after a rain (even the indoor rides will have wet seats in those conditions, because people with wet ponchos and wet clothing will be sitting there), or just blotting moisture from our own faces.
- TOURING. Plan on early mornings and late evenings to take advantage of the coolest times of day, and structure your touring so that if you are in a fully or mostly outdoor queue or show (e.g., Slinky Dog Dash, Seven Dwarfs Mine Train), you're hitting them first thing in the morning or last thing at night. The rest of the day, you'll just be passing from one air-conditioned attraction (or store, or show) to another. From mid-morning to mid-afternoon when the heat and humidity are at their peak, go back to the hotel and get a nap or enjoy some pool time -- or, if showers are causing a mass exodus of guests, pop on your ponchos and take advantage of the shorter attraction queues and the post-rain drop in temperature!
- HYDRATION. Staying hydrated is important, but I'd caution against bringing numerous, heavy bottles of water with you everywhere and toting them around in the heat. Instead, take regular refreshment/drink breaks at counter service locations, where you can always get iced water for free on request, and won't have to add several pounds to your park bag load.
Case in point: In August 2021, DH thought he could get away with a light "water-resistant" raincoat. As you can see, when we got caught in a little squall on the way back to our hotel, he ended up soaked from chest to knees, and his backpack (which couldn't fit under his coat) and suede Vans sneakers were too. (His sneakers were still wet after 24 hours: he ultimately had to run them through the dryer.) The kids and I, resplendent in well-made reusable ponchos and wearing quick-dry mesh slip-on sneakers or Tevas, stayed high and dry.