@elilla great tips. As someone who often does hard exercise in hot and humid weather, there is a point where your body literally cannot absorb liquid fast enough, so you'll dehydrate even if you drink as much as you can.

It can be quite difficult to notice the signs if you you're not used to it (and, even if you're used to it) so be careful with intense workout in very hot and humid weather. If you feel like you have to throw up, cool yourself down and stop the workout right away.