We were there this past July 5-9 and it was two things: HOT and HUMID. It was honestly 95 degrees at 7am one day...I'm just not used to that!! LOL!
We did fine though, much to my surprise. Some things I found to be key:
-Drink TONS of water
-Take plenty of breaks
-Take advantage of indoor attractions
-Take a mini-fan, or a misting fan...they were lifesavers!
-If possible, take a mid-afternoon break back to the hotel. Get a nap, take a dip in the pool, or at the very least, take a quick shower and freshen up. It was a lifesaver (especially with a 4 yr old).
We encountered a lot of the tour groups, but they weren't bad. I'd heard horror stories on here, but all the kids we encountered were very nice, lots of the girls were smitten with my DS for some reason....maybe 'cause he's blonde haired/blue eyed and that's not the norm in Brazil? LOL The sheer size of the groups can be annoying IF YOU LET IT BE...but we were just happy to finally be at WDW and didn't mind.
I'm not gonna lie, it's hot, but it's manageable. I'm excited to see what it's like there when it's not a bazillion degrees...we're going back in 3 weeks and I can't wait!!!