In the summer it rains on many days, but it usually will not rain the whole day through. A typical summer day will be mostly sunny in morning, building clouds throughout the early afternoon, and then rain (sometimes very heavy with lightning) for an hour or two in the mid to late afternoon or evening. It will typically clear again after that. Of course this is just the trend, and anything is possible.
Also, you'll be visiting during hurricane season, so that's a possibility as well. Either way it will be HOT! This August most days have been around 100-105 with the heat index, so a little cloud cover and rain should be welcome.
Enjoy the trip!
