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Aucklanders can expect more stuffy nights this week as the heatwave continues, but there's a chance of showers too.
Weather Watch head analyst Philip Duncan said the North Island will remain hot and settled, but humidity levels will increase from today.
"It is likely to get very muggy early this week, which can make the temperature feel five degrees more than it is. That could make for some uncomfortable sleeping.
"A large low could bring showers on Monday evening or Tuesday morning, which is good news for baches relying on rainwater, and for farmers.
"There is a chance of showers also on Thursday. It is only a matter of time before the rain comes."
The South Island is likely to experience more unsettled weather this week. It would be predominantly warm and windy, but could fluctuate between higher and cooler temperatures.
Weather analyst Richard Green said the sea temperature has reached 22C in Auckland, slightly above average for February. Wellington and Christchurch sea temperatures stood at 17C.
"We are in a weak La Nina pattern so we do not expect significant change in sea temperatures in the coming months," said Mr Green.
North Canterbury was the warmest spot in the country yesterday, reaching 38C. Hanmer Springs and parts of Marlborough made it to 36C.
Auckland's high was 29C but with stiflingly high humidity levels.
Mr Duncan said it was rare for New Zealand temperatures to approach or reach 40C more than once a summer.
"Twice in January and once in February we have seen close to 40 degrees, which is unusual."
Smoke from South Australian bush fires has also had an impact on the South Island with a thick orange haze seen in the sky. Queenstown residents reported a "strange orange glow" in their region.
High temperatures, strong winds and low humidity were also a perfect recipe for fires in New Zealand, MetService spokesman Bob McDavitt said. The MetService advises people to check local fire and water restrictions.
- ADDITIONAL REPORTING: NZPA
