The Great Barrier Reef climate varies between the northern and southern extremes of the area.
With the exception of a few islands in the very south of the Great Barrier Reef Marine Park Authority boundaries, the entire Reef lies within the tropical belt between the Tropic of Capricorn and the Equator.
This means that temperature and climate in the great barrier reef is sub-tropical in the south, getting more tropical as you head north.
Unlike temperate regions, tropical and sub-tropical regions don't experience the four seasons; instead there are just two - a wet season and dry season.
The wet season ('The Wet', as it's affectionately known to the locals...) occurs between the months of November to March when up to 2 meters of rain can fall on Cairns over the 5 months.
The southern regions don't suffer quite so much, Brisbane typically sees around half that amount.
Of course, as everywhere, there are local anomalies. The Tully / Innisfail region south of Cairns gets a higher-than-average soaking, while Townsville and Magnetic Island see less rain because they are sheltered by the mountains.
The most unpleasant characteristic of a tropical climate wet season is without doubt humidity. This can get unbearable during the height of The Wet, when temperatures can get to a very muggy 30 degrees Celsius all along the coastline.
During the wet season, the months of December-February are the wettest and also play host to Cyclone Season, although thankfully these huge storms aren't too frequent over the Great Barrier Reef.
Heavy seas whipped up by a cyclone (the tropical name for a hurricane) can wipe out large areas of coral reef in shallower waters.
Spectacular electrical storms are often the case during these months - in fact some of the best lightning in the world occurs over northern Australia!
The dry season therefore is a much more comfortable time to visit the area. The months of July, August and September are the best when temperatures average a very pleasant 20 degrees Celsius - slightly warmer in the north than in the south but not much in it.
Humidity and rainfall are at a minimum during these months and sunny days dominate. The nights are cooler but not cold, with average nighttime temperatures at between 10 - 15 degrees Celsius.
The chart shown below gives you an easy comparison between general climate trends for Cairns (the northern end of the Great Barrier Reef) and for Brisbane (at the southern end):