What’s so weird about Tropical Cyclone Alfred?

Tropical Cyclone Alfred started off life in an unusual way, born in the South Pacific as a triplet, alongside siblings Rae and Seru.

Alfred has some other quirks to its name — least of which is that it should have been called Anthony, but wasn’t allowed to be named after the prime minister.

So what’s so unusual about TC Alfred?

Alfred formed with two other cyclones in the South Pacific

While it’s not unheard of for three tropical cyclones to form out of the same trough, it is rare, especially in the South Pacific.

Tropical Cyclone Rae headed towards Fiji causing damage to some islands before weakening, while Seru passed by waters off Vanuatu before dissipating.

“It was very active across the southern hemisphere, it wasn’t just what happened in the South Pacific,” Professor of Atmospheric Sciences at Monash University Liz Ritchie-Tyo said.

“Two cyclones formed around Madagascar, the other end of the South Indian Ocean, so there was actually a lot going on all at once.”

There’s a lot we don’t know about tropical cyclones, largely because before the existence of satellites they were difficult to measure and track.

“Until we got satellites up there, we didn’t even know about half of them were out there,” Dr Ritchie-Tyo said.

“We understand them pretty well as individual beasts. It’s really about when we look at long-term trends, we just don’t have those historical records to allow us to do that.”

How fast is Cyclone Alfred moving?

Most cyclones hit Australia’s east coast hard and fast, but Alfred has been taking a different approach, moving slowly parallel to the coast.

As of the latest BOM advice from Wednesday morning, Cyclone Alfred was moving west at 16 kilometres per hour.

That’s allowed it to whip up prolonged and broad reaching areas of large swell over the last few days.

While surfers have been making the most of the waves, its also led to warnings of significant coastal erosion and flooding for low-lying areas.

Nearly 1,000 km of the east coast is under coastal hazard warnings from the Bureau of Meteorology, from Forster in New South Wales all the way to Sandy Cape, near Bundaberg.

Waves of over 10 metres have already impacted the K’gari and Rainbow Beach regions of Queensland.

“[Alfred] is already producing quite high waves and swell even up onto the Brisbane coast,” Dr Ritchie-Tyo said.

“That’s probably one of the things that we’re going to be looking at is, how much coastal erosion damage Alfred does.

“And that’s not something we always see from our landfalling tropical cyclones.”

Loading…

Dr Ritchie-Tyo said the dramatic waves and swell were unlike other tropical cyclones.

“Normally you would see a very concentrated wind field and a fairly fast approach on the land, whereas Alfred’s coming down the coast,” she said.

“So it’s been coming parallel to the coast, [which gives its winds] a lot of opportunity to be pushing southerly swell up the coast and onto the coast, even though it itself has been off over ocean.”

Is it normal for a cyclone to make landfall this far south?

Despite northern parts Queensland being well versed in cyclone crossings, it’s been over 50 years since a tropical cyclone has made landfall in south-east Queensland or northern New South Wales, and for good reason.

Though it’s not abnormal for cyclones to reach the latitudes of south-east Queensland, Dr Ritchie said the prevailing winds through the southern half of Australia tended to push any cyclones born in the South Pacific away from the mainland.

“So they’re more likely to track over New Zealand than they actually are to come in on the Australian coast,” she said.

Those that do manage to stay near Australia also tend to run into conditions that don’t make life easy for a cyclone once they track further south.

This includes the relatively cooler waters further south, which weaken the cyclone, and unfavourable winds through the atmosphere which cause a cyclone’s tall, vertical structure to rip apart.

Warm waters — over 26.5 degrees Celsius — and “low vertical wind shear” are two of the crucial ingredients needed for a cyclone to form, intensify and stay alive. 

A good source of moisture in the atmosphere is also required to sustain a cyclone — something readily available in the tropics at this time of year.

Dr Ritchie-Tyo said Alfred had managed to find itself in a meteorological sweet spot, where all the ingredients were coming together to keep it alive and close to the coast, with winds causing it to take a U-turn back toward the mainland.

She said this in itself made Alfred an “unusual cyclone”. Though she noted Australia does see “a lot of unusual cyclones” if you look closely.

Is climate change impacting Tropical Cyclone Alfred?

While climate change is supercharging the ferocity of cyclones, the impact isn’t as clear-cut as other natural disasters like fire and floods.

What scientists do know is that a warmer, wetter and more energetic atmosphere is giving cyclones more destructive power.

They are also moving — observations have shown both where cyclones form as well as where they reach their maximum intensity has been moving away from the equator in recent decades.

Dr Ritchie-Tyo said a lot of what we do know is from research conducted in the northern hemisphere.

“There’s suggestions that what we call the tropical belt will extend further south and that means … potentially the atmospheric circulation that tropical cyclones like to exist under will also extend further south as well,” she said.

“But once again, there’s a lot of uncertainty, in the southern hemisphere in particular, we don’t really have a lot of good answers.”

As ocean temperatures warm up, the conditions needed for cyclones to hit further south increase, with a temperature of 26.5C required.

“We have a very sharp, ocean temperature gradient. That tends to mean that once cyclones move far enough south, they weaken pretty quickly,” Dr Ritchie-Tyo said.

“As temperatures warm up, that does mean there may be better conditions for cyclones to make it further south.

“They do seem to be tracking further south already and making it further south.”

But there could be other factors at play.

“It could be because the conditions are actually more conducive to them, living that long and being able to move further south,” Dr Ritchie-Tyo said.

“It could just mean that we are tracking them for longer.

“Our records make it a little bit difficult for us to be completely sure why that might be.”