Hello Katy,
We have cruised twice in August and is our favorite time of the year, along with Feb/Mar. Yes the weather will be very warm and extremely humid, much like that of south florida in the summer. It is also a little risky as one day you may have gorgeous weather and the next you may find yourself avoiding a very bad storm. There's a healthy chance you may encounter rain, for 10-20 minutes a day, but the weather is gorgeous most the other time. It will be hot though, very hot, the sun is intense around this time. If you have ever been to southern florida in july/august, then this is the best description I can provide in relation to the weather. Enjoy and I hope this helped your decision.