Okaaaay, so I asked for this thread to be re-opened because Townsville and Cairns are slightly/very different. In short, Townsville is dry and hot whereas Cairns is humid and hot - Cairns is about twice as bad because of this. It feels like you're sweating on the inside sometimes... hence for anyaccomodation that you get here I would HIGHLY recommend making sure it has air-conditioning. In Townsville the heat can be overcome by turning on a heap of fans and hiding in the shade, in Cairns the heat will follow you.
Something else that's good about JCU in Cairns though is that for one there's a good pool across the road, and regardless of where you are there's somewhere good to swim within about 5-10 minutes drive (beaches, crystal cascades, Ross and Locke, Stoney Creek) . That and the fact that the heat usually only sticks around until about the middle of March and then starts coming back around the middle of October mean it's pretty easy to deal with if you're smart about it - obviously don't go for a run in the middle of the day, is what I'm saying. Basically, if you're staying in Cairns just for the academic year then you'll avoid the majority of it.
Some people will probably say that Cairns is quite bearable without A/C but personally, after having lived here for 17 years, I'd say they're insane and probably just don't know any better. As for adapting, you never really get used to it in the sense that you can walk out in 30 degrees and 80% humidity and be like "What a nice cool day this is" but you'll learn to deal with it in other ways (clothing choices, finding airconditioned places etc.) within about 30 seconds of arriving.
N.B. This isn't to say that Cairns is unbearably hot, because it isn't. It's just a lot more comfortable with air-conditioning