Temperatures in Rotorua and the Bay of Plenty soared this week, with several centres reaching 30C or above.
According to Niwa, the hottest temperature in the country on Monday was 32.1C, which was recorded at Kawerau, followed by 32C at Whakatane.
Rotorua weather man Brian Holden said Rotorua had an un usually high temperature of 30.8C. He said although it was a high temperature for the city, it wasn't a record.
Mr Holden said Rotorua's highest maximum temperature on record was 35.2C which was "some time way back in the early 1900s''.
The city also managed to reach 31.5C in January 2004 and January 1983.
Niwa climate scientist Georgina Griffiths said there had been only 21 days warmer than Monday's maximum, since records began 100 years ago.
"It's a notably warm day,'' she said.
It was the hottest day this summer, far surpassing the 27.7C recorded on December 19.
"That's a big jump. The Bay of Plenty often gets 28C but anything over 30C is unusually warm ... it's not surprising people are running for the beach.''
But the scorching conditions will make way for heavy rain and gales this week, as a west to southwest flow spreads across the country, said MetService.
MetService forecaster Philippa Murdoch said: "Basically the warm temperatures over much of the country over the last couple of days have been due to a very warm air mass spreading over the country from Australia.
"Now it's starting to move away and there is more of a south westerly flow over the country bringing in a bit of slightly cooler air.'' .
The front is expected to bring rain, stronger winds and gales to central parts of the country and exposed parts of Northland and Auckland before moving to the South Island.
Meanwhile, things were a little different in Taupo.
Windy and dry conditions made for a difficult day for holidaymakers and boaties yesterday and Monday with strong winds battering the district and the Taupo District Council asking people to conserve water and not light fires.
The warning came after a blaze in a rural area near Kinloch on Monday night burned 5ha of bush and scrub. It took 35 firefighters battling the strong winds and dry conditions to bring it under control.
The Taupo District Council asked people not to light any fires anywhere yesterday as winds continued to blow strongly.
The council also asked residents and visitors in Taupo to try and save water as the strong winds were impacting on the area's water supply.
The wind had churned up Lake Taupo, causing pumice and debris to block the main water intake on Lake Terrace.
Staff worked through the night last Monday to remove the debris, but the water flow was still reduced and would cause problems for firefighting, if a blaze occurred.
Out on the lake, southwesterly winds gusting up to 40 knots whipped up 2m swells on Monday but did not appear to cause many problems for boaties.
Harbourmaster Philip King said although the high winds had been forecast they came in very suddenly.
To the relief of those holidaying in tents, the wind began to abate from midday yesterday.
A staff member at Lake Taupo Top 10 Holiday Resort said although a couple of campers had asked to move to more sheltered sites, the campground's fences helped protect it and no tents had been blown away.