Australia Weather News

There is a high probability Cyclone Alfred, currently around 1,000 kilometres offshore, will cross one of the most highly populated stretches of the Australian coast next week.

While the Bureau of Meteorology's official forecast track only extends four days ahead, weather models, which predict pressure systems up to two weeks in advance, are in solid agreement the system will turn towards Queensland this weekend.

This movement west should lead to Alfred's final destination next week somewhere in the vicinity of the east coast, most likely between about Brisbane and Townsville — a path which could include a direct hit on Mackay, Rockhampton, Hervey Bay, Bundaberg, Gladstone or the Sunshine Coast.

How a cyclone can be forecast seven days ahead

Alfred currently poses no immediate threat to Australia, however considering a cyclone's life span can stretch to weeks and systems can drift thousands of kilometres, meteorologists are eagerly analysing Alfred's potential movement next week.

So what controls a cyclone's path? 

Weather systems are influenced by the environment they occupy and interactions with adjacent systems.

In the case of a tropical cyclones, while their ferocious winds and rain are self-sustaining due to the energy gained from warm seas, their movement is dictated by the winds and pressure of surrounding weather systems.

Alfred currently exists in a quiet neighbourhood — with no jet streams, fronts and slack winds — typical for the tropics. 

During this pattern, without steering winds, a cyclone is left to follow the path of least resistance, drifting very slowly into the weakest opposing flow, which is currently leading Alfred on a slow track south.

The critical question is, how will the surrounding weather impact the track next week?

The key is an upper high, the term used to describe a high-pressure system a few kilometres above the ground, over the mainland.

Since winds blow anti-clockwise around a high in the southern hemisphere, the high's positioning to the south should draw Alfred towards the coast this weekend, and if the high lingers, which modelling predicts, eventually a path onto the Queensland coast.

However, there is danger in relying on traditional weather models to predict cyclones, since even the slightest change in the strength or location of a surrounding system could lead to a major shift in the eventual path.

The solution is to use what's called an ensemble forecast, which is generated by running a model dozens of times with slightly different initiation conditions, then using the results to show the spread or confidence in the possible scenarios.

Below are two ensemble displays for Alfred into next week.

The first shows individual trajectories from the GFS ensemble, which favours a slow right turn towards the coast this weekend then a likely landfall in around a week, most likely on the central Queensland coast.

The next map shows a strike probability for Tuesday, March 4, from the European Centre for Medium-Range Weather Forecasts (ECMWF) — the best in the business when it comes to forecasting and it clearly shows a favoured track to the central Queensland coast.

While this seems to suggest a cyclone is imminent, several ECMWF ensemble members (individual forecasts in the ensemble), do keep Alfred off the coast.

How powerful will Alfred become prior to landfall

By late Tuesday, Tropical Cyclone Alfred was a category two system with maximum wind gusts to 140 kilometres per hour.

The forecast for Alfred is that intensification will continue sporadically for another 24 hours due to:

Later this week wind shear will increase, and the atmosphere will become less humid — two factors which should lead to a weakening and will hopefully result in category one or two rated cyclone if landfall does indeed occur next week.

While a category two might not sound too threatening, at this strength Alfred would still lead to destructive winds and possibly widespread major flooding.

However, while great advancements have been made in the accuracy of cyclone tracks over recent decades, the skill of cyclone intensity forecasting is lagging due to the delicate balance between opposing forces, along with a knowledge gap in the complex physical and chemical processes within a system.

A final word from AI — look out Brisbane

Artificial Intelligence models are now challenging traditional models for accuracy.

Rather than solving trillions of mathematical equations which represent the atmosphere, they just look for trends after being trained on decades of weather maps.

There's too many AI models to cover, but one of the best is GraphCast from Google DeepMind, and for what its worth by Tuesday next week, it places Alfred less than 200km off the coast of Brisbane.