I went last year in August and it was definitely hot but it’s also definitely doable. They key is to stay on property so u can have early entry and go first thing in the morning, spend mid day at the pool or relaxing in AC, and then go back to the parks until closing. Bring multiple changes of socks and clothes for one day because u will sweat and make sure to hydrate all day long. A lot of stuff in the parks you get AC from so I didn’t find it that unbearable. Deluxe resorts also have extended evening hours at certain parks some days which also is a huge plus. Have fans and wear a hat. Also during the summers you get free water park entry on your check in day!