People should expect the ever-changing weather to continue over the coming week, with NIWA warning of "wild swings" that will be "next level" bringing days of hot temperatures but then cold winter weather.
The weather around the country over the past week has been a mix of beautiful sunny hot days and wintry weather.
Over the past few days, the east coast of the North Island has been in the firing line for wild weather.
On Tuesday night, residents in the small town of Waikohu near Gisborne were told to self-evacuate, New Plymouth flights were cancelled and Cook Strait ferries were scrapped because of the wild weather.
But then last week, Wairoa in Hawke's Bay hit 29.6C - easily breaking the North Island's previous heat record for September.
NIWA forecaster Chris Brandolino told AM on Wednesday this ever-changing weather is typical for spring and is set to continue because of El Niño.
El Niño occurs when the ocean surface temperatures in the Pacific Ocean rise above normal levels. It brings more frequent, dry westerly winds, increasing the chances of drought.
It comes after New Zealand had La Niña for three consecutive years, which is "pretty unusual", Brandolino said, and was a big reason behind the wild weather earlier this year like Cyclone Gabrielle.
Brandolino told AM co-host Laura Tupou spring is a really variable season so it's not surprising Kiwis are seeing ever-changing weather.
"It's that three-month period where mother nature is handing the baton from winter to summer," he said.
"What we're going to see is these quick swings where we go from 29.6C to snow and that happens a lot in spring.
"But what this is, this is next level. This is spring El Niño style where we get these wild swings and we're already seeing it now. We'll get these really warm temperatures and then the bottom drops out and because there's so much variability, we're also going to have a lot of wind."
Brandolino had bad news for people looking for some fine weather over the coming days with more rain and wind on the way.
"What we're going to see over the next few days, we have cool temperatures, showers. It's a far cry from last week. This weekend, we're likely to see some really strong winds in the upper North Island," he said.
"Saturday is going to be an awful day weatherwise. I mean, there's going to be wind, there's going to be rain. Some of that wind could be damaging wind, cold temperatures and it will really feel more like July or August than it will September or October."
He told AM this changing weather is a theme of what New Zealand is going to see throughout spring and into summer.
The ever-changing weather comes during the first week of the school holidays with families crying out for fine settled weather.
But Brandolino said families will have to wait until the end of next week for some settled weather.
"Monday and Tuesday, we warm back up. We see more wind for the South Island. Then we get cold again for Wednesday and people who are on school holidays may be wondering when can we catch a break and get some nice weather?
"Mum, dad, kids, I think from about Wednesday, Thursday of next week, right to the last week of school holidays, that's your time to be outdoors."
Looking ahead to summer, Brandolino said El Niño will bring dryness, particularly for the North Island.
"We're concerned about dryness, particularly for a good chunk of the North Island," he said.
"So Northland over toward the Auckland Region, the Coromandel, Hawke's Bay to Tairawhiti/Gisborne, Wairarapa, upper South Island, Eastern South Island."
Watch the full interview with Chris Brandolino in the video above.
