Tauranga is on track for its warmest February on record - and the scorching days may linger.
The city is no stranger to high temperatures and has already equalled its 2011 record with an average of 21.7C - with four days to go. Temeratures yesterday reached 25.1C.
Hamilton, Wellington and Dunedin are also on track to break records.
Hamilton has so far recorded its hottest temperatures in 42 years. Hamilton's average of 21.7C is so far beating its average February record of 21.5C, set in 1974.
Wellington's average of 19.6C is also beating its 1998 record of 19.3C, and Dunedin is beating its 1999 record of 17.1 with 17.9C.
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Auckland is its fourth warmest average on record at 22C. The record was set in 1998 with 22.5C.
Christchurch has been its second warmest on record at 18.8C. Its 19.7C record was set in 1998.
Forecasters say the scorching days and cloying mugginess could linger until at least mid next month but weather analysts are divided about what's causing it.
The MetService said El Nino was responsible; Niwa and WeatherWatch argued bouts of rain this summer were out of character for an El Nino season.
MetService and WeatherWatch acknowledged that climate change could be playing a part, but a longer trend of rising temperatures will be needed to confirm that so, for now at least, super-hot summers are not "the new normal".
Meteorologist Georgina Griffiths of MetService said yesterday that with four days of the month to go, four of the six main centres were on track for their warmest February on record.
The previous hottest February in all but two of the major cities was in 1998, the last time there was a "super-strong El Nino".
Ms Griffiths said it was normal for an El Nino summer to have such a high number of February days with temperatures topping 25C, but the slow creep of climate change was probably playing a part as well.
"Climate change is a long, slow escalator underlying everything. In the short term we have steps up and down - cold seasons, warm ones, because of bog-standard weather," she explained.
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"We got a step up because of the El Nino but there's probably an underlying climate change thing there too."
Ms Griffiths said high temperatures would linger until at least mid next month, when a warmer-than-usual autumn would begin.
The pattern of dry spells broken by rain was likely to continue.
Niwa scientist Chris Brandolino said preliminary predictions indicated the start of next month would be hot and sticky, with humidity in the North Island, and thunderstorms.
A brief cool-down would follow at the end of the first week for much of the country, followed by "settled weather and abnormally warm weather" in the second week.
WeatherWatch head analyst Philip Duncan agreed with Niwa, saying although El Nino could be responsible for hot, dry weather on New Zealand's east coasts, wet weather in other parts of the country was more like a La Nina year.
Meanwhile, Cyclone Winston could finally be petering out. Winston dropped to Category 2 yesterday and WeatherWatch believed it would probably lose its cyclone status altogether at some point yesterday or today.
The track to New Zealand was still unclear, as it had been for half a month now, but Mr Duncan said it was likely Winston would pull down tropical air over the country this weekend, which would merge with a cold front and bring heavy rain to some North Island areas.