How Cyclone Alfred came to threaten Queensland’s biggest city

The first cyclone to directly threaten Brisbane in half a century is the result of a very specific set of weather conditions. Is climate change among them?

For the first time in half a century Brisbane is facing a direct hit from a tropical cyclone, thanks to a recipe of warm seas, moist air, a monsoon trough and light winds.

Not since cyclones Wanda and Zoe delivered a double blow to southeast Queensland in 1974 has Brisbane faced such a looming threat in the form of category 2 Cyclone Alfred.

Senior meteorologist Dean Narramore said it was unusual but not unheard of for cyclones to extend beyond the tropics, with it all coming down to a very specific set of conditions within the monsoon trough.

He said that amounted to southeasterly winds on the south side and northwesterly winds on the north side, plus a cluster of thunderstorms forming along the trough.

“In that situation the northwesterly winds and southeasterly winds can cause a rotation so those storms start spinning and concentrating around that central point,” Mr Narramore said.

“If all conditions are right, that will become the eye of the cyclone, and cyclones are vertically stacked, meaning they’re perfectly aligned through the depth of the atmosphere.”

He said cyclones intensified when there was no wind in the atmosphere but plenty of moist air, and the sea surface temperature remained at 27 degrees or above.

“Dry air can impede a cyclone’s development and we have seen a lot of dry air to the north side of Alfred in the last couple of days, but we’re now seeing that moisture fully wrap around the cyclone,” Mr Narramore said.

“The winds are strongest around the eye wall, or the inner core, because that’s where all the air is coming in and rising up before evacuating out the top, sometimes as high as 40,000 or 50,000 feet.”

Erosion at the mouth of Pumicestone Passage looking towards Bribie Island as Cyclone Alfred continues to approach southeast Queensland. Picture: Lachie Millard

University of Queensland senior lecturer in the school of environment, Annie Lau, said the lower sea temperatures in the southeast meant Cyclone Alfred was unlikely to get much stronger than a category two storm.

However, she said that still posed a significant threat to infrastructure, which was not built to the same standards as that in the state’s north.

“The building code is a bit different in the south, so we may not have as robust buildings as they do in northern Queensland, where category four and five cyclones are a regular occurrence,” Dr Lau said.

There was a view the southeast could see more cyclones in years to come, as sea temperatures rose in response to climate change.

University of Newcastle associate professor Iftekhar Ahmed said some of the effects of climate change were at the point of no return, and the impacts would become more severe if allowed to continue unabated.

“We are going to have a much warmer planet and much warmer seas and erratic cyclonic activity around the world,” Professor Ahmed said.

“We’re already there, and if we don’t stop it now it’s going to get worse.”

But Dr Lau was not convinced Cyclone Alfred was directly related to climate change, pointing out the southeast experienced a series of cyclones in the 1970s.

As well as Wanda and Zoe in 1974, Wendy and Daisy struck in 1972 and, 18 years before that, the great Gold Coast cyclone walloped Coolangatta.

“It’s hard to say whether this is a result of climate change but if we keep having warm water in the subtropics we will have a higher likelihood of tropical cyclones coming to us,” she said.