Heatwave, cyclone, omega blocks: Unique weather pattern to wreak havoc in Australia

This week, a heatwave, tropical cyclone and high pressure system will collide to wreak weather havoc Australia-wide.

A “unique” weather pattern, in which a heatwave, tropical cyclone and high pressure system collide, is set to cause a tumultuous week of weather across Australia.

With the cyclone and heatwave already underway, the key to understanding this wild weather trifecta is a little known concept called an omega block.

The term describes a broadscale weather pattern in which an area of high pressure is straddled on either side by areas of low pressure. The phenomenon is called an omega block because, on a synoptic chart, the isobars form a shape similar to the Greek letter omega (Ω), as per Weatherzone.

An illustration of an omega block pattern. In the southern hemisphere, the omega shape appears upside down. Picture: Weatherzone.

“Omega blocks tend to cause severe weather because they slow or block the passage of weather systems that are trying to move from west to east across Earth’s surface,” Weatherzone explained.

And Australia has not just one of them on the cards, but two.

Forecast models show two omega blocks that are expected to form around Australia later this week and, in combination with Tropical Cyclone Jasper and a heatwave, cause some destruction. By Sunday evening, one of the blocks is expected to straddle the eastern half of Australia while other sits over the Pacific.

Two omega blocks are expected to influence Australia’s weather this week. Picture: Weatherzone.

You can see one omega sitting over eastern Australia, and the other over the Pacific Ocean. Picture: Weatherzone.

That means, from the second half of this week and into next, meteorologists expect a prolonged heatwave to grip a large part of the country.

“This will affect part of every mainland state and territory,” Weatherzone said.

In particular, temperatures in Western Sydney are expected to reach the low-40s on Saturday. That’s on top of an ongoing heatwave that saw temperatures soar to 45.9C on Monday in Warburton, WA and reach 45.6C in Tarcoola, SA on Tuesday.

The pair of omega blocks will also influence Tropical Cyclone Jasper, which was declared on Tuesday afternoon, pushing the storm towards Queensland’s east coast.

“While there is still a lot of uncertainty around the future movement of this system, the presence of the upper-high increases the likelihood that it will track towards eastern Australia,” Weatherzone said.

A heatwave is already underway. Temperatures in the pink regions are tipped to reach 44C or higher by Thursday. Picture: Weatherzone.

Finally, the omega blocks may also cause a low to pass over SA, which is “likely to cause a mix of dangerous weather, possibly including heavy rain, severe thunderstorms and damaging winds,” Weatherzone said.

A heatwave has already begun to boil over a staggering one-third of Australia, with temperatures in large parts of the interior expected to exceed 44C.

Extreme heatwave conditions are mostly isolated to the WA-SA border and around Broome, while low-intensity and severe conditions are expected to spread across the country from the west to east over the coming week.

Meanwhile up north, Tropical Cyclone Jasper has been confirmed 1500km northeast of Cairns and is moving slowly towards Queensland.