More details please.
Although I'm not the OP, I was about to post his question nearly word for word (well, we're maybe not quite as senior as he, but getting close).
We've done our share of diving around the hot spots, and we're quite spoiled (that last trip to Raja Ampat really did it - now, diving anywhere else looks just kind of
meh...). But we have never been to Australia yet and of course the GBR is high on our list. W've been thinking about a 3 week trip there around Christmas 2013. That date was floated just because it's probably easier for us to get a long stretch of time off from work then, and because we figured it would be summer there, and thus "nice weather". However, my wife casually mentioned her plan to an Australian co-worker (who I think also dives) and he gave her a concerned look and told her something along the lines of, "you know, if you go then, you're gonna get rained on, don't you?" So now it's occurred to us that we ought to do a little more research into the best/worst dive seasons before we take a year-and-a-half to plan a major trip there.
My personal opinion is that if you're making a trip like that, 3 weeks is the minimum amount of time that's necessary to make it worthwhile for me - it's a long way to go, I won't get to go there often (I wont say "once in a lifetime" but practically speaking, I'm not going to be able to go back often). So I want to make sure our trip is as successful as it can be.
So, setting aside for the moment any constraints we might have that could limit or complicate us getting 3 weeks in a row off from work...what are the best times to do a trip there? We're planning to have about 2 weeks to spend along the NE coast of Australia/GBR; we're planning a liveaboard (not sure on any details yet) and maybe some additional shorter trips out. The focus of our trip will definitely be diving the GBR, but we plan to spend some time (probably about a week) sightseeing on land, too.
Best times to dive? Worst times to dive? Advantages and disadvantages of going during the period around Christmas (say, early December through early January)? When would you go if you could go anytime?
Thanks for any advice!