A year on from the extreme heat, drought and bushfires that greeted the start of 2020, the weather has generally shifted back to longer-term averages, Blair Trewin, a senior climatologist at the Bureau, said.

“2020 [was] a much more normal year than 2019,” Dr Trewin said.

While final figures will be released next week, NSW’s 2020 was the mildest year for daytime temperatures since 2012. Average daily temperatures were about 0.76 degrees above the 1961-90 yardstick used by the Bureau.

For Australia as a whole, 2020 was the fourth hottest on record for mean temperatures and fifth hottest for maximums. Both measures trailed the scorcher in 2019 that smashed many records.

NSW’s annual rainfall last year of 636 millimetres was back above the long-run average for the first time since 2016, with totals more than double those in 2019.

The Bureau declared such a La Nina to be under way in late September and “we’re seeing a fairly typical La Nina signal” now, Dr Trewin said.

During La Ninas, rainfall tends to shift westwards along the equatorial Pacific, pushing rainfall totals above normal levels for most of eastern Australia, including NSW.

That means, according to the Bureau’s longer-term outlook, most of NSW can expect strong odds of higher-than-normal rainfall for the first quarter of 2021.

“A few areas will miss out” but for most of the state that means rain gauges will likely be fuller than usual for these months, Dr Trewin said.

With all the cloud around, the state’s daytime temperatures are likely to be average to even cooler than normal, except for areas close to the coast. That’s true for most of the rest of Australia.

Overnight temperatures, though, should remain on the mild side for the next few months for most of the country.

One risk during La Ninas is for more tropical cyclones than usual, which can decay and make their way south to NSW, lifting the risk of flooding.

The Bureau’s Ms Reid said meteorologists are monitoring the development of a low-pressure system in the Gulf of Carpentaria, which could become the season’s first tropical cyclone for Australia.

Another feature of La Nina years is that, while heatwaves can still happen across southern Australia, they tend to pack fewer days of extreme heat.

Instead, “you can get more prolonged spells of moderate heat,” Dr Trewin said, adding “there’s no indication of any significant heat in the near future for south-east Australia”.

Even though La Nina tends to be on the cooler end of the natural variation, the background warming from climate change means that even the cool years remain relatively warm on a local and global scale.

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