The strange thing about Cyclone Debbie
THERE was a point earlier this summer when Aussies in the Top End started to wonder: Where the hell are the cyclones?
The Australian region is usually hit with 11 cyclones each season - which runs from November 1 to April 30 - but only five tropical cyclones have been named in 2016-17. The 2015-16 season was the least active on record, with only three tropical cyclones declared.
In other words, it had been eerily still.
That was until today, when a Category 4 monster will hurtle towards the Whitsundays.
The region is expected to endure destructive winds, gales and a dangerous storm surge when the cyclone hits after midday.
The latest research into cyclones suggests that this will become the norm: fewer cyclones, but the ones that do form will be more destructive than ever.
That means stronger winds, more ferocious storms and heavier rain.
Cyclones need a very specific set of conditions in the atmosphere and ocean to form. Climate change has made those conditions harder to find, which is likely to lead to fewer tropical cyclones around the world, according to University of Melbourne cyclone expert Associate Professor Kevin Walsh.
One of the key conditions is sea-surface temperature above 26.5C and cool conditions in the upper part of the troposphere, which is found 15km above sea level.
"Climate change is causing the upper troposphere to heat up even more, and so the atmosphere becomes more stable," Dr Walsh told the university's Pursuit website.
This means that warm air on the top of the water won't rise as fast, so it's less likely a cyclone will be created.
While this might sound like good news, the bad news is that the ones that do form will be more intense than what Australians are used to.
"The thermodynamic conditions in the atmosphere are likely to be slightly more favourable for more intense storms," Dr Walsh said.
"So, the most intense storms are likely to have great wind and storm surge impacts, including a substantial tendency for more rainfall."
HOW DO CYCLONES FORM?
A tropical cyclone is a large, spiral weather pattern that forms over warm tropical waters.
It is a low-pressure system that has sustained winds of 63km/h or more and gusts in excess of 90km/h near its centre, according to the Bureau of Meteorology.
The gale force winds can extend hundreds of kilometres from the cyclone's centre.
The eye of the storm, which is typically 40km wide, has light winds and often clear skies.
The dense ring of cloud that surrounds the eye brings with it the strongest winds and heaviest rainfall.
Tropical cyclones can have unpredictable paths and last for days. They usually break up when they hit land or cooler waters.
"Tropical cyclones form when a small low-pressure system in the tropics, through a combination of favourable atmospheric and oceanic conditions, is able to strengthen by extracting energy from the upper part of the ocean," Dr Walsh told Pursuit.
"The ocean acts like a steam engine boiler - creating warm, moist air.
"Because the upper part of the troposphere (about 15km up) is much cooler, the warm air rises, and the rotation of the Earth starts the spiral forming.
"If other conditions are favourable, a cyclone forms.
"The ocean needs to be warm (tropical cyclones almost always form in the tropics); the atmosphere needs to be moist; they need some rotational energy from the spin of the Earth (they don't form right on the equator, where there is no such rotational energy); they need wind patterns in the atmosphere that support the vortex rather than tearing it apart.
"Getting all of these conditions right is rather rare, which is why there are typically no more than about 90 tropical cyclones per year, worldwide."