I was there the Christmas before last and it never went below 37. With high humidity. I remember it well because my fellow travellers who were born up there thought the weather at 39 was 'great'.
I like Port Douglas, but in December it's about 39 degrees every day with high humidity and the ocean is too hot to swim in. And then there are the crocs and stingers. July is much better.
If July, hire a yacht or take a cruise from Monte Carlo through the Mediterranean, Sardinia, Bocche di Bonifacio, Portofino. Heaven on earth. Crystal clear water, private beaches, star spotting. A glimpse into how the uber-rich and royalty live.