This will sound overly simplistic, but just plan on it being hot. I don't mind it as much some, plus we find time to duck inside a store or a restaurant with AC.
Most of our trips end up being June-sept. In June we've had several days at 100, but also times it was mid to high 80s. I think typically though it will max out in the 90s with afternoon storms here and there.
Hot & Muggy. Average highs tend to be 90-92 with a heat index close to 100. Evenings will be around 72-74. Expect rain showers everyday between around 2-5 but normally do not last very long. It comes down hard and fast and then generally clears up.