I am traveling in August because of kids in College/High School. I think the Mediterranean is not as fun for them, and Alaska more boring. ALso with 5 people and living in the East Coast the Caribbean is cheaper.
Yes, it will be hot, but it depends on what you call hot. The islands are cooler because of the ocean and you will be swimming most of the time anyway. While on the ship, you can stay in the air-conditioning if its too hot for you to sit on the deck.
Don't worry about it. Its no hotter than August in the states...
After our southern Caribbean cruise last August, I told all my friends in hot, humid Nashville that if I EVER complained about the humidity here again, they should slap me.
The excursions that are land-based can be uncomfortable if you are not in air-conditioned vehicles -- and some of them do not have AC. While we were in St. Thomas and St. Maarten, we would occasionally go into a store to look just to get some cool air from the AC.
That being said, as Jim said, if you're in the water, on the beach, or on the ship, you should be comfortable.
You didn't say where you're from, except the east coast. I've been to New York City in August and it's very hot and humid. I've also been to St. Louis in July and experienced over 100 degree days, much worse than tropical weather. The Caribbean is warm and humid, but it's near the water so you probably won't experience temperatures over 90 degrees. The water is refreshing and most caribbean shore excursions involve the water.
We visited Cozumel in March and did the Tulum Ruins excursion. The weather was great. I know I wouldn't have chosen that tour in August. Pick your excursions carefully, don't try to do too much in a day, carry a water bottle with you (I bring one from home and fill it before getting off the ship), and you'll have a wonderful time.
Hey, this is Bill, and I live in South Florida where it is hot/humid pretty much all year. What part of the states are you from?? Since it is hot across the country in August, I don't think the difference will differ greatly from where you live.
To mirror what Jim and Mooneydiva stated, make sure that you ride in an A/C vehicle. Plus when you are exploring, the breeze off the watyer is very nice, not too hot. One thing I did was bring a couple bottles of water with you. Keep yourself hydrated.