Take the forecasts with a grain of salt! On our last two visits, we had forecasts of rain nearly every day -- and never saw a drop of it! There were times when we'd walk out of an attraction exit to find that there'd been a brief shower while we were inside, but that was it.
Keep ponchos/mini-umbrellas with you in case you need them, and wear footwear that works well in wet conditions (e.g., yes to waterproof hiking sandals -- no to leather sandals, sneakers or Crocs, which become incredibly slippery when wet) but otherwise, just tour as you would otherwise and have a good time. A few of the outdoor attractions do close down when it's raining, so you might need to tinker with your plans a little, but it shouldn't have a huge impact on your day.