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You'll need a year to see Australia so I guess that's why they give people so long.

You don't want to be at the top end (north) of Australia in the wet season. Cyclones don't you know. So, 1 May to 1 November should be ok. Outside of those times it can be hellishly hot and humid and the chances are it buckets down with rain all the time. Besides, if you go up there in summer it'll be stinger season and those things kill. (Box jellyfish including the deadly https://en.wikipedia.org/wiki/Irukandji_jellyfish)

Visibility on the GBR is dependant upon weather factors but generally it's pretty good. If you're in Cairns for a little while you can pick and chose the days you go. They have large tour operators with lavish boats and seafood lunches, right down to small operators in powered and sail boats. It's about 4oknm off shore though, so don't go in some pokey little dinghy, it'll take all day to get there.

https://www.australia.com/en/places/cairns-and-surrounds/guide-to-the-great-barrier-reef.html

Sure appreciate this info. Good engagement topic sir.