At the time, the Bureau of Meteorology (BoM) said the storm could be categorised as a “bomb cyclone”.
Though it did not make landfall, its effect on the weather across parts of Australia showed the hefty impact these winter storms can have.
Despite the similarities in name, bomb cyclones have some key differences to their tropical cousins, and are often more dangerous – so what exactly are they?
A bomb cyclone is a non-tropical – also known as an extratropical – cyclone that develops extremely rapidly from a low-pressure system.
It forms when there’s a swift pressure drop, with a decrease of at least 24 millibars (which measures atmospheric pressure) over 24 hours – an event known as bombogenesis.
Most are formed in the Northern Hemisphere, particularly off the coasts of the US and Japan, but Australia’s east coast is also battered by them.
They are most common in winter, with cold continental air and warm, moist ocean air providing the energy for a cyclone to develop.
What makes a bomb cyclone dangerous?
Compared to normal non-tropical cyclones, bombs are better at converting energy into motion.
Even if they don’t make landfall, they bring dangerous winds and surf and cold weather to nearby landmasses, as one did for south-east Australia in August this year.
The rapid development of a bomb cyclone makes it harder to forecast its exact intensity and timing, which increases the risks to life and property.
Do bomb cyclones often hit Australia?
There are about 70 bomb cyclones annually worldwide, though the ones that affect Australia’s east and south coasts tend to be less rapid-forming than their Northern Hemisphere equivalents.
On average, two thirds of the bomb cyclones that form every year are north of the equator.
What’s the difference between tropical and extratropical cyclones?
Tropical cyclones, of course, are more closely associated with Australia’s northern regions and have dealt great damage to towns and regions over the years.
From a practical point of view, the difference between the storms is largely to do with temperature.
Extratropical cyclones, including bomb cyclones, are associated with cold and warm fronts, and are “cold-core” meaning they are colder at the centre than at the fringes.
By contrast, tropical cyclones are warm-core, but largely have little temperature change across their mass.
They derive their energy from latent heat release generated by cloud and rain formation from tropical air.
Tropical cyclones also have their strongest winds near the ground, while extratropical cyclone winds are strongest near the “tropopause” – between nine and 17 kilometres above the surface of the earth.
Is climate change going to affect bomb cyclones?
Extratropical cyclones on the whole are expected to shift closer to the North and South Poles in the future, which would mean fewer such winter storms in Australia.
Fewer studies have examined bomb cyclones specifically, but some suggest they have become more frequent, particularly in the Southern Hemisphere.
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Some research has indicated that bomb cyclones will also move towards the poles, however.
Australia’s East Coast Lows are expected to become less frequent due to climate change, particularly during winter – which is when bomb cyclones typically form.
However, rising sea levels and atmospheric moisture could potentially make those that do form in the future even more dangerous.