New Zealand has sweltered in the grip of a heatwave this week: and now people in some parts of the country can say they've experienced an official one.

A heatwave, as defined by the UK MetOffice, occurred when the daily maximum temperature exceeded the average maximum temperature by 5C or more for five consecutive days.

What that "average maximum temperature" was depended on the average for specific locations – and specific times of the year.

Such lengthy spells of warm or hot temperatures were considered rare in New Zealand.

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But MetService meteorologist Georgina Griffiths said there was now enough data to confirm an official heatwave had taken place in inland Bay of Plenty, Marlborough, and parts of Canterbury, including Cheviot, Culverden and Tekapo.

Griffiths said a number of other locations that had experienced consistent heat for three or more days were also likely to record official heatwaves.

They included Pukekohe, Hamilton, Taumarunui, Taupo, Palmerston North, Wellington, Porirua, Nelson, Dunedin, Gore and Invercargill.

Griffiths said regardless of the academic definition, many Kiwis would have felt a heatwave this week.

"For most people, it will qualify."

Meanwhile, Niwa's latest monitoring showed soils were drying up in many parts of the country.

Across the North Island, soil moisture levels decreased everywhere during the past week due to meagre rainfall and extremely warm temperatures.

The most significant decreases were observed across the northern two-thirds of the island, with less substantial changes having occurred in the lower North Island.

The driest soils across the North Island compared to normal for this time of the year were found in the Far North, while the wettest soils for this time of the year are located in a portion of Hastings District.

Areas deemed hotspots had expanded "significantly" during the past week in the North Island, Niwa reported.

A large hotspot now encompassed all of Northland and northern Auckland, while another one now covered much of northern Waikato along with the Coromandel Peninsula.

Other hotspots were in place in central Manawatu-Whanganui, Wellington City and Porirua, Mahia Peninsula, and a small portion of Tararua District.

Across the South Island, soil moisture levels generally decreased in northern areas, although small improvements were observed in interior Otago, Southland, and Stewart Island.

The driest soils across the South Island compared to normal for this time of the year were found in western Tasman and northern Buller District, while the wettest soils for this time of the year are found in north coastal Otago, near Invercargill, and Stewart Island.

For people who were sick of the hot, dry weather, a brief respite is on the way.

MetService is forecasting a front to bring rain to many parts of the South Island tomorrow and a few showers about the North Island on Saturday.

This front would also be accompanied by cooler air bringing temperatures back to average for this time of year this weekend, with some reprieve from warm and muggy overnight temperatures.

The front will also bring some severe weather with it, with severe weather warnings for strong wind in Canterbury High Country, including the foothills, Otago, Fiordland and Southland early on Friday.

Although the warnings were focusing on the winds preceding the front, the southerly expected behind the front is worth noting as it will be briefly strong along the east coast of the South Island and central New Zealand as well.

"We could see some brief southerly gales behind the front with strong gusts all the way through to central New Zealand," MetService meteorologist Kyle Lee said.