Unusually warm ocean surface temperatures around the North Island are signalling a muggy shift to the start of summer.

Surface temperatures in some parts of New Zealand have reached up to 3C warmer than what is expected at this time of year.

With summer just days away, Aotearoa has already experienced soaring temperatures this week.

MetService said temperatures for the next couple of days will reach sweaty highs in the high 20s and low 30s across the country.

Stifling nights were also forecast to plague Kiwis, with forecasters potentially considering issuing heat alerts.

What does this mean for NZ?

Earth Sciences New Zealand ocean modeller Erik Behrens told the Herald most of the North Island will be impacted by these warmer ocean temperatures.

Particularly Auckland, Northland, Tauranga and the Bay of Plenty area, he said.

The ocean surrounding the North Island is sitting between 2C to 3C above normal, and the Hauraki Gulf sea surface temperature has reached 20C.

“It’s quite unusual,” he said.

Due to these temperatures, he said Kiwis will be in for a muggy start to the summer, and if it rains, that rain may be heavier.

“It’s not just this region, but it sort of stretches really all the way to Australia and further north to Pacific Islands,” Behrens said.

Unusually warm ocean surface temperatures around the North Island are signalling a muggy shift to the start of summer. Image / Earth Sciences New Zealand

Behrens said the warmer ocean will cause warmer air and potentially bring an increase in rainfall.

“It goes hand in hand. So if the ocean is warm, then land temperatures also tend to be warmer.

“At the same time, warmer ocean basically allows more water vapour to evaporate. So basically could also mean increased rainfall, stronger rainfall. That is sort of what physics would tell us,” he said.

He said the ocean temperatures have already been warm for the past few months, but not as “intense” as they are right now.

“Now it seems to become very intense. Before it was 1C or 2C, and now we suddenly see 3C above average.

“It seems to be on the up instead of down,” Behrens said.

La Nina or El Nino?

Earth Sciences New Zealand said El Nino and La Nina are opposite phases of a naturally occurring global climate cycle.

These phases influence rainfall, temperature and wind patterns around the world, including New Zealand.

Behrens said it was too early to tell whether this year will be La Nina or El Nino.

“It’s tending towards La Nina, but they haven’t decided yet.

“This [La Nina] is a phenomenon which usually only kicks in during summer season. At the moment, we are still a bit too early for that to have a large impact on New Zealand.

“I think there is no relationship yet,” he said.