Simple guide to Qld’s weird and wild weather

Five tropical lows, multiple cyclone threats and colliding tropical waves. The weather is getting weird and wild in Far North Queensland. We break down exactly what is going on.

• What it’s like inside a cyclone

Five tropical lows are likely to develop off northern Australia in coming days with one already off Cairns, triggering a 350mm downpour and heightened cyclone risk.

The rare event is being caused by two key weather drivers – or tropical waves – known as the Madden Julian Oscillation (MJO) and an equatorial Kelvin Wave.

We sat down with the Bureau of Meteorology’s Kimba Wong to break it down for you and to explain what was likely to unfold in coming days.

What are the contributing factors to the tropical lows around northern Australia?

Two planetary waves heading towards Australia in the equatorial region were the main broad weather drivers likely to aid cyclone formation.

The Madden Julian Oscillation (MJO) and the Kelvin Wave both travelled west to east and could be influential in priming the atmosphere for active monsoonal periods.

How the Madden-Julian Oscillation works. Picture: Met Office

The Bureau defines a Madden Julian Oscillation as a fluctuation in tropical weather on weekly to monthly timescales.

Characterised as an eastwards moving pulse or wave of cloud and rainfall near the equator, the oscillation recurs every 30-60 days.

Meanwhile, the Kelvin Wave can be an alternating low to high pressure centre moving along the equator.

This animation shows a series of waves, called Kelvin waves, moving warm water across the equatorial Pacific Ocean from west to east during March and April. The signals can be an early sign of a developing El Niño, and were detected by the Sentinel-6 Michael Freilich sea level satellite. Credit: NASA/JPL-Caltech

But Ms Wong said the waves colliding near Australia was not enough – another trigger was needed to form a cyclone.

“The waters around tropical Australia at the moment are very warm and for cyclone formation, we typically need sea surface temperatures over 26C in order for it to be warm enough,” she said.

“Those warm ocean temperatures are really the fuel that drives tropical cyclones, or the energy source.”

Air surface circulation was also needed to trigger the formation of a cyclone.

“But what we need in order for a cyclone initially to possibly develop, is surface circulation,” she said.

“That could happen when a surge in south-easterly winds meets a surge in monsoon or north-westerly winds.

“The leading edge of those two surges, because of the opposite wind directions, can result in a circulation forming at the surface. That drives the convergence of low level winds. And if you know winds are bumping into each other, they sort of have to go up, because they can’t go sideways.”

What is a tropical low?

Tropical lows have lower wind speeds than tropical cyclones but can still bring severe thunderstorms and lots of rain. The moderate-strength low-pressure systems occur in the tropics, often in the monsoon trough.

What and where are the five tropical lows?

Forming around Queensland:

13U

This low is currently the closest to Cairns and has a moderate chance of forming into a tropical cyclone over the weekend. By Saturday, there is a 25 per cent chance (moderate chance) that 13U will form into a cyclone.

12U

By Sunday, this tropical low will also have a 25 per cent chance of forming into a cyclone and was likely to develop in The Gulf of Carpentaria later in the week.

16U

By Monday, 16U would reach a 30 per cent chance of turning into a tropical cyclone.

The system will form further out in the Coral Sea and is tipped to not have a huge impact on Queensland’s weather by itself

Five tropical lows forming over northern Australia. Picture: BOM

Not forming around Queensland:

14U

This tropical low will likely have a low chance of forming into a cyclone well into next week. The event was tipped to remain on the northwestern side of Australia and would not likely have any influence on Queensland.

15U

By Tuesday, February 4, 15U will have a 30 per cent chance of tropical cyclone strength but will likely remain on the northwest coast of Australia. Although 15U would most likely pass to the south of Christmas Island and the Cocos (Keeling) Islands, it could enhance shower and thunderstorm activity in the area.

Which tropical low is likely to turn into a cyclone?

All five tropical lows have a chance of forming into a cyclone over the next week and a half but only 16U and 15U will reach a 30 per cent chance of tropical cyclone strength.

Do we have a name for the potential cyclone?

While none of the tropical lows have formed into a cyclone just yet, the Bureau of Meteorology had identified three names ready to be used.

Taliah is the frontrunner on the cyclone-naming list, followed by Vince and Zelia.

However, should a cyclone form outside of Australia’s area of responsibility, another country would name the weather event.

Accumulated rainfall for the next 7 days leading up to Monday, February 3, according to ECMWF

Which towns are likely to be affected more in northern Queensland?

“Broader parts of northern Queensland are going to see the influence of these systems. But where exactly the heaviest rainfall will be or the strongest winds – I guess there are elements of uncertainty at this stage,” Ms Wong said.

“There is quite a high likelihood that we’ll see periods of heavy rain and potentially quite dangerous flash flooding and riverine flooding developing in the North East Queensland catchments.

“Between Cairns and even as far south as Bowen or Proserpine may see some increase in rainfall on the periphery of these systems over the next few days.

“On Saturday and Sunday, the area between Townsville and Innisfail looks favoured to see a focus on the heavier rainfall as well. So any of those towns really could see the brunt of these systems there.”