Those struggling in the heat won't find any respite in coming days as temperatures are forecast to soar to 30C.
Even when the mercury dips into the 20s, humidity levels will mean it feels much warmer.
MetService meteorologist John Law said the high dew point, which is a measure of humidity, was a consequence of the subtropical northerly air flow and warm seas that had combined and wrapped themselves around New Zealand. It is deemed uncomfortable when the dew point goes higher than 18C.
Overnight temperatures over the next week would remain around 20C, meaning steamy sleeping conditions. Law said the general weather pattern causing the uncomfortably sticky nights was set to remain through February at least.
"It's shaping up to be a very hot month and we will have to start looking at some [temperature] records, I think. And it's been equally as hot at night," Mr Law said.
He said daytime temperatures in Northland were well above the January average of 24C and well above the night-time average of 15-16C for the month.
"Northland is used to having a warm January and tropical temperatures but this has been particularly warm for a long period."
Part of the reason for the above-average warm weather was the fact that any southerlies to hit the country were on the back of the subtropical low, so had not brought in cool, dry air from Antarctica. Rather, they had just recycled the warm air from ahead of the low.
But if it's too warm on land, take advantage of the ocean, which has heated up to between 21C and 22C off Northland's coastline. This is also above average for this time of year.
Weather for Northland's Anniversary weekend looks good, with Saturday and Sunday mainly fine with southeasterly winds and a high of 27C. Monday's temperature dips slightly to 26C while showers develop on Tuesday and with rain on the radar for Wednesday, Thursday and Friday.
Wairarapa is likely to be the hot spot on the North Island today, with a predicted high of 33C for Masterton, with only very light wind offering respite from the heat. Temperatures were expected to dip only into the high 20s over the next few days but be back up to 31C on Monday.
Gisborne faced 32C today, with a little more comfort overnight, dropping to 19C.
MetService meteorologist Tom Adams said Hawke's Bay too would swelter in a tropical air mass for the foreseeable future.
"It is looking quite hot and sunny for the next wee while. Temperatures are definitely going to get pretty warm, especially as we go into next week.
"It's a little bit cooler when a southerly goes through on Friday, with temperatures of 27 degrees, but by the time we get to Tuesday next week it will be back up to 29 degrees and then hit 30 degrees on Wednesday."
Overnight temperatures today and tomorrow would hover at 20C and only drop to 18C at the end of the weekend before rising to 21C next week.
"It will be relatively humid because we're in a tropical air mass and with those high temperatures it will feel quite sticky," Adams said.
"There is a weak southerly coming through on Friday but it's not really going to make much of a difference to temperatures in Hawke's Bay. There might be a few showers, particularly inland."
The warm weather was driven by high pressure sitting over New Zealand.
"Something that's going to drive temperatures up for a lot of places next week is the high shifting across to the east, and particularly as south-northwest winds take over.
"When northwesterly winds take over it increases the wind temperatures because the air is going up and over the mountain ranges."
The North Island would also be affected by warm air being dragged from the tropics at the end of the week, he said.
"What is looking likely is there will be some warm air coming down from the north which will contribute to the warm temperatures in Hawke's Bay."
It was possible the region would receive rainfall at the end of the week but the quantity was yet to be determined, Adams said.
In the Bay of Plenty, only "a little bit of cloud" was stopping Tauranga from becoming one of the hottest spots in the country, Adams said.
"It is looking particularly warm next week ... it is still going to feel very humid," he said. "It is going to be 20C or over every night for the next week."
Despite the humid temperatures, a severe thunderstorm watch remains in place for the Bay of Plenty.
Residents have been hitting local ice-cream parlours and beaches to cool off.
Tina Junger, who owns The Big Avocado in Katikati, said the shop had sold about 100 real fruit ice-creams, which was more than usual.
"We have our regulars, and we have people who refer others to us because they think we have the best real fruit ice-creams in the country," she said.
"Throughout January and all through the summer period it [ice-creams] is a big part of our business."
Pete Grindrod from Tay Street Dairy said he had been "flat out" selling ice-creams and coffees, and had definitely been busier than usual today.
"The weather is pretty extreme," he said. "Being on the beach and being weather dependent it is definitely busy here today. Can't complain."
Grindrod said he had rolled about 9000 ice-cream cones in the past month and had lost count of how many he had sold yesterday. "It has just been a continuous amount."