The La Nina weather pattern is causing flooding in parts of New South Wales and Victoria and forced Sydneysiders to dodge hail during a severe thunderstorm on Friday.
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But what exactly is La Nina?
La Nina and its opposite pattern El Nino are phases of a natural climate cycle in the Pacific Ocean, known as the El Nino-Southern Oscillation.
La Nina occurs when east-moving trade winds go into overdrive, strengthening a process called upwelling where deep cool water is drawn up to the surface.
This results in cooler-than-usual waters in the central and eastern tropical Pacific near South America, while warmer waters pile up in the western Pacific near northern Australia, encouraging tropical cyclones to form there.
This temperature difference also strengthens an atmospheric loop known as the Walker Circulation, where warm air rises in the west and cool air falls in the east.
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The Bureau of Meteorology's Dr Andrew Watkins said the result is that the Walker Circulation gets stronger.
"The oceans get more cool water drawn up from below and then the Walker Circulation gets stronger again. And you can get a positive feedback loop between the ocean and the atmosphere, and that's what creates that locked-in pattern of La Nina over the tropical Pacific," Dr Watkins said.
While El Nino occurs once every two to seven years, La Nina tends to occur in consecutive years, meaning that this weather pattern could last into 2022.
La Nina can have varying effects as it typically brings more severe drought and fires to southern United States but more rainfall and cloudiness to Australia.
Australia had its wettest two-year period on record during the 2010-2012 La Nina event, which caused catastrophic floods in Queensland.
Dr Watkins described La Nina as "a bit of a mixed bag".
"You improve on the fire side but you do see more flooding and tropical cyclones," he said.
Meanwhile, climatologists believe climate change could intensify the impacts of a La Nina weather pattern.
"Climate change means that for every degree of warming that we get, the atmosphere can hold roughly 7 per cent more moisture, so we might expect to see greater rainfall when the rain comes, particularly during those extreme events like tropical lows and tropical cyclones where effectively it's sucking moisture from a broad area and then dumping it into a relatively small region," Dr Watkins said.
Shivé Prema
I am a video journalist and host of the Newcastle Herald TikTok account! I spend most of my days filming and editing videos but also like to write articles as well. I'm new to Newcastle, so I like to spend my spare time exploring this city and its many beaches.
I am a video journalist and host of the Newcastle Herald TikTok account! I spend most of my days filming and editing videos but also like to write articles as well. I'm new to Newcastle, so I like to spend my spare time exploring this city and its many beaches.
