Some days can be ok, but it can get pretty hot - especially with the humidity.
The trick is to keep trips outside to relatively short jaunts.
If you're out for the afternoon, keep it to no more than 30-45 minutes walking (with plenty of water), followed by 45 mins or so in an airconditioned area. If your hotel is centrally located, it can help, because then you can keep popping back when you need to.
Hotel lobbies or shopping centres can be great for finding good airconditioning.
Overall, it's quite bearable, if you're careful.
Oh, and keep a hat on when you're drinking all that water!!