New Zealand just had its warmest, wettest winter on record

New Zealand has marked its warmest winter for the third year in a row, and its wettest on record.

According to data from Niwa, the nationwide average temperature was 9.8C – 1.4C above the 1981 to 2010 average.

Of the 10 warmest winters on record, six have occurred since 2013.

This winter’s highest temperature was recorded in Wairoa on August 20 with 24.3C, and the lowest in Aoraki/Mt Cook on July 17, with -11.6C.

It was also the wettest winter on record due to a number of extreme rainfall events that resulted in severe flooding and slips across the country – 42 locations across the country experienced a record or near-record wet winter.

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Niwa meteorologist Ben Knoll said the warmth was likely here to stay.

“We feel like a broken record – the weather maps are always red,” he said. “It’s pretty concerning to see that successively, season after season.”

What’s caused all this rain? All winter we have been in the midst of a global climate system called La Niña.

According to MetService, when La Niña is active, there is an increased frequency of rainy weather systems approaching New Zealand from the north.

A negative Indian Ocean Dipole (IOD) occurred alongside this, further increasing the potential of northerly rainfall events. Forecasters expect this to ease over the summer months.

Usually lows cross the country quickly and move eastward, caught up in the overall westerly atmospheric flow. But high pressures east of New Zealand have been slowing the departure of weather systems – and as those systems linger, they continue to drop rain.

Finally, there’s the background increase in temperature due to climate change. A warm atmosphere has the potential to rain more heavily than a cooler one, as warmer air can transport more water vapour – that is, more fuel for rain.

Other findings from Niwa’s winter summary include:

• This winter’s highest temperature was recorded in Wairoa on August 20 with 24.3C, and the lowest in Aoraki/Mt Cook on July 17, with -11.6C
• Coastal seas also had their warmest winter on record, with persistent marine heatwave conditions
• Aoraki/Mt Cook Village had its deepest snowpack on record (since 2010) in mid-July
• The sunniest four regions in 2022 (so far) have been Taranaki (1701 hours), Bay of Plenty (1675 hours), Greater Nelson (1621 hours) and Auckland (1564 hours)