Yes Robinw, it's definitely hot up there in Feb, average about 29C - 32C and humid through summer, (even yesterday it was 30C and it rained! Minimum was 22C). In most of Queensland, winter/spring is nicer, not as humid. It actually rains more thru summer/autumn (Nov-April) and averages about 25C - 28C. August would be pretty good, drier and slightly cooler than in May (ave max about 26, min about 17 in Cairns, 22 and 10 respectively in Brisbane). I think it was about that time of year I last visited. It was cool in Sydney though, so it depends if you plan to go elsewhere as well. Hope I haven't confused you too much with all these stats!
Here's some links for you to check out - www.greatbarrierreef.aus.net/ and www.tropicalaustralia.com.au/visitor and
www.tq.com.au
Happy surfing! Let me know if you have any more questions, always happy to spread the word about Australia!