Autumn outlook: NZ to get 'one last taste' of summer

A beachgoer at Auckland's Mission Bay makes the most of late-summer weather last month. More warmth is in store this month. Photo / Dean Purcell

New Zealand's slide into autumn is to start with a stretch of settled, summery weather – with drier conditions forecast for the North Island in particular.

Niwa's latest outlook for the next three months is picking above-average temperatures everywhere except the east and north of the South Island, along with periods of "warm, summer-like" conditions this month.

"For folks who've endured some cooler temperatures this week, we'll flip that back around – so everyone will get at least one more taste of summer weather from roughly the second week of March, through to the middle of the month," Niwa meteorologist Ben Noll said.

"Places like Canterbury that have arguably had a bummer-summer compared with other parts of the country may get some pretty toasty temperatures around that part of the month too."

Even after big rain-makers like ex-tropical cyclone Dovi delivered some much-needed moisture, "hot spots" of notably parched soils had since returned to parts of the North Island, with dry or very dry conditions now found across much of Northland, Auckland, and Waikato.

"They'll be holding out for some more rain – but they'll probably have to wait until at least the second half of March to get their next chance."

By late March and early April, more unsettled weather and an unseasonable cold spell could play out.

The sun rises on meteorological autumn in Aotearoa New Zealand 🌅

Our climate station at Upper Hutt dipped to a cool 5.1˚C this morning, which is more typical of May. pic.twitter.com/wV0e9krkrj

— NIWA Weather (@NiwaWeather) February 28, 2022

Elsewhere in the forecast, Niwa predicted the gradual exit of two major drivers of our summer warmth.

Before winter, a second consecutive La Niña climate system was expected to fade away, with oceans around the equator reverting to "ENSO-neutral" conditions.

As well, coastal waters that have warmed to "marine heatwave" conditions would slowly begin to cool – but not without delaying the seasonal shift to colder temperatures, while raising the odds for stormy weather.

As at last week, marine heatwaves were still unfolding in the northern and western North Island and western and eastern South Island, while sea surface temperatures across the whole of the country ranged from 1C to 1.6C above average over February.

Last month, Moana Project and Otago University oceanographer Dr Robert Smith said this summer saw among the strongest marine heatwave conditions in New Zealand since satellite observations began in 1981.

"With temperatures reaching 4 degrees above average, a marine heatwave off the North Island west coast in mid-December blew all records for at least the last 41 years," he said.

Marine heatwaves weren't just a calling card of La Niña, but also climate change.

It's now been more than 60 months since New Zealand saw a month of below-average temperatures – and last year was our hottest on record.

As for rainfall between now and winter, Niwa reported totals were likely to be near normal or below normal in the north and west of the North Island, near or above normal in the west of the South Island, and most likely to be near normal in all other regions.

And while three ex-tropical cyclone systems have veered near the country this season, that didn't mean another one wouldn't visit over the period.

"Any activity during early March is not expected to impact New Zealand, although there will be another chance in late March or early April," Niwa reported.

"As the country has experienced several times in recent months, these systems can cause extreme rainfall and flooding."

Noll said late March would coincide with a driver of rain and thunderstorms that circled the globe every 30 to 40 days, called the Madden-Julian Oscillation, or MJO.

"That will definitely be a period to monitor. Whether it results in the next tropical cyclone or atmospheric river, we can't really see that far into the future."