But generally, such lengthy spells of warm or hot temperatures were considered rare in New Zealand.
WeatherWatch.co.nz forecaster Philip Duncan expected upper parts of the South Island – including Nelson and Marlborough – along with inland areas of Hawke's Bay might end up having experienced a heatwave in the technical sense by the week's end.
"A heatwave isn't so much a big high: it's consistently hot weather, day after day, often without the wind blowing, and that's what's been bringing these areas close to that technical heatwave criteria," he said.
"People in Nelson have been telling me, especially at the start of the week, how it's been very hot and dry for them.
"Likewise, I've had a lot of people in Napier telling me how blown away they've been at how it has been there."
While it had been awfully hot in the main centres, Duncan believed they wouldn't have experienced an official heatwave this week.
"But, in saying that, I don't think humans measure things that way: it's definitely been an abnormal weather event, and that's why everyone has been calling it a heatwave."
MetService meteorologist Georgina Griffiths said it was too early to say which locations might meet the criteria, but expected that data to be available over coming days.
But she echoed Duncan's point that, regardless of the academic definition, many Kiwis would have felt a heatwave this week.
"For most people, it will qualify."
Meanwhile, the country is set for a brief respite of cooler weather this weekend as New Zealand enters the "peak" of the heatwave today.
Temperatures in the South Island were cranked to the max yesterday, with Cheviot reaching 36.1C - New Zealand's warmest temperature this summer - Pukaki (Mt Cook) reached 34.8C, Hurunui 34.4C and Masterton got to 32.7C.
Niwa said today would be the "peak" of the heat wave, and predicted temperatures could reach 37C in parts of North Canterbury.
MetService meteorologist Hannah Moes said today's top main centres were forecast to be Blenheim in the South Island on 34C, and Masterton in the North Island on 33C.
But many more spots were tipped to top 30C, a trend the country has experienced since the heat began on Sunday.
"Today is looking very similar to the past few days, apart from some cloud in the morning and at night it is looking fine for most places," Moes said.
Niwa's high-resolution model was forecasting a max temp near 37C in North Canterbury and 34C in the Wairarapa.
The country's eastern centres were looking to be the pick of the bunch again, with high temperatures boosted by the foehn effect as the air mass passed over the country's central mountain ranges.
The exceptions to the fine weather were gale northerlies forecast about Fiordland and strengthening westerlies in central New Zealand.
MetService meteorologist Lisa Murray said some respite from the heat was coming for parts of the country in the form of a punchy southern system.
"We are still under this ridge of high pressure, what we are seeing is a slight increase in winds," she told the Herald.
"We've been seeing these sea breezes in the afternoons cooling things down, sometimes by as much as 10 degrees.
"What we're going to see now is as the new front approaches the winds will pick up over Fiordland and other places gradually and then across the country."
The front is expected to slide northeast across the South Island and the lower North Island which will bring gale-force winds to many areas tomorrow.
But the run of warm weather isn't over, another ridge of high pressure is expected to arrive over the country on Saturday and Sunday.
Today's weather
Whangārei
Fine apart from morning and evening cloud. Easterly breezes. 25C high, 18C overnight.
Auckland Fine and warm, but some cloud morning and night. Easterly breezes. 27C high, 18C overnight.
Hamilton Fine and warm, but some cloud morning and night. Light winds. 30C high, 16C overnight.
Tauranga Fine apart from morning and evening cloud. Light winds. 25C high, 18C overnight.
New Plymouth Fine with light winds, then some evening cloud. 24C high, 17C overnight.
Napier Fine and warm. Northeasterly breezes. 27C high, 19C overnight.
Whanganui Fine with light winds, then some evening cloud. 28C high, 18C overnight.
Wellington Fine apart from late cloud. Northerlies gradually picking up. 24C high, 18C overnight.
Nelson Fine. Northerly breezes. 26C high, 17C overnight.
Christchurch Morning cloud clearing to fine. Northeasterlies. 27C high, 17C overnight.
Dunedin Becoming fine in the afternoon. Northeasterlies, strong at times. 27C high, 13C overnight.
