Queensland is bracing itself for a second cyclone of the summer with a low pressure system expected to intensify later on Wednesday into Tropical Cyclone Kirrily.
The storm comes after Tropical Cyclone Jasper caused devastating floods in far north Queensland in mid-December.
Experts say the likely formation of Kirrily is being boosted by unusually high temperatures at the surface of the ocean in the Coral Sea.
So what are the origins of the soon-to-be cyclone Kirrily, and how does it fit into the broader trends for cyclones under global heating?
What’s happened with Kirilly?
On Wednesday morning, the Bureau of Meteorology said a low pressure system – currently called 05U – was likely to intensify into a tropical cyclone by late Wednesday or early Thursday and to cross the Queensland coast on Thursday night.
The cyclone would cross somewhere between Cardwell and Bowen with the most likely destination “in the Townsville vicinity” as a category-two system – a slight downgrade from a category-three system that was being forecast earlier this week.
Category-two cyclones have maximum winds of between 89 and 117km/h and gusts of up to 164km/h – high enough to cause damage to homes, crops and risk power failures.
The most severe weather from coastal crossings of cyclones tend to be on the south side of the system, the bureau said, with a region between Ayr and Mackay earmarked for severe winds within 24 hours of Wednesday morning.
Where the system will head next is less certain for later this week, but the bureau said even as a “tropical low” it would still bring “heavy to intense rain” to parts of central and western Queensland.
What are the origins of Kirrily?
Brad Jackson, a senior climatologist at the bureau, said the expected cyclone had started its life as a low-pressure system over the Gulf of Carpentaria early last week before moving east into the Coral Sea.
Sea surface temperatures in the Coral Sea have been well above average for this time of year and this was helping the system to “spin up” into a cyclone.
“Warmer temperatures increase evaporation and will feed more moisture into a system,” Jackson said. “That’s why we are looking at this [system] spinning up. If you have a tropical low over warm sea surface temperatures it will draw in more moisture and energy.”
Sea surface temperatures in the area of the Coral Sea where Kirilly was forming were between 2C and 3C above average for this time of year, Jackson said.
“That’s reasonably warm and, in an El Niño year, is quite unusual,” he said. “Usually sea surface temperatures in an El Niño would be cooler than average [in that region].”
Prof Michael Reeder, a meteorologist and cyclone expert at Monash University, said cyclones were dependent on sea surface temperatures and tended not to form when ocean temperatures were below about 26.5C.
Temperatures in the ocean have been rising for decades due to global heating and the global average sea surface temperatures have been at record levels since March 2023.
Back-to-back cyclones?
Kirilly is likely to be declared only six weeks after Tropical Cyclone Jasper made landfall north of Port Douglas on 13 December.
Jasper and Kirilly have formed in the eastern region of Australia that typically sees four cyclones form each season between November and April.
In October, the bureau said there was a 76% chance the eastern region would see a below average number of cyclones for this current season.
But it is not uncommon for consecutive cyclones to form relatively close together.
Queenslanders will remember 2011 when category-five cyclone Yasi – one of the biggest storms ever to hit the coast – arrived only four days after category-two cyclone Anthony.
What’s happening to cyclones in Australia?
Dr Andrew Dowdy, an associate professor and expert on tropical cyclones at the University of Melbourne, has published several studies on cyclones in the Australian region and recent trends.
For a long time, the prevailing wisdom in Australia has been that El Niño years tend to deliver fewer cyclones than summers influenced by La Niña.
But Dowdy says there are signs this relationship is weakening and this “makes seasonal prediction of tropical cyclones a bit more challenging these days”.
“It has been many years since more tropical cyclones than average occurred in the Australian region,” said Dowdy.
“That is even with several La Niña events in recent years that should have helped increase the chance for higher than average cyclone numbers.”
Both globally and in Australia, studies suggest the numbers of cyclones that form is going down.
As the planet warms from the burning of fossil fuels and deforestation, climate scientists expect to see fewer cyclones forming, but those that do form will likely be more intense.
“When you have more heat and energy in the ocean and atmosphere, that drives more intense systems,” Jackson said. “So we may only get one cyclone [a year] for example, but it could be a really big system.”
Dowdy says climate change will also worsen the impacts from tropical cyclones. Rising sea levels will worsen inundation from storm surges caused by cyclones, and the rainfall from cyclones is also likely to intensify in the future.
