A NIWA meteorologist says it's "a distinct possibility" that temperatures in New Zealand could rise to more than 40degC for the first time this summer next Tuesday.
"It's in the conversation," Chris Brandolino told the AM Show on Friday.
"Monday is going to be hot, but Tuesday is where the heat's going to be at its highest.
"I'm not going to promise [40degC], but it's certainly a distinct possibility. I wouldn't say it's a likelihood, but it's in the conversation."
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The hottest temperature ever recorded in New Zealand is shared by Marlborough and Rangiora, which both peaked at 42degC.
Mr Brandolino says while warm air can often increase the chance of a thunderstorm, he doesn't believe there will be much more than a few odd showers.
The massive high set to strike the country next Tuesday is caused by three coinciding factors, he says - wind coming from the north, warm ocean temperatures and climate change.
Mr Brandolino told The AM Show last month that ocean temperatures around the country had been around 2degC hotter than last year, and up to 6degC warmer in some parts.
"When you have the alignment of all these three things, you get these extreme results," he said.
"Let's remember, 2016 was the warmest year on record in New Zealand, and 2017 was the fifth-warmest on record - so we've had two top-five finishes in the last two years."
Parts of the east of the South Island reached 37degC yesterday, with Hanmer Forest getting to 36.2degC - their warmest January temperature on record, going back to the early 1970s.
And Mr Brandolino says the extreme heat comes off the back of two of the hottest months in New Zealand history.
"December was the second hottest December on record, in terms of the seven station series we use to evaluate the country's temperature," he explained.
"January is shaping up to be not only the hottest January on record, but also the hottest month of any month - going back to 1909."
He says temperatures could be so warm that our mean temperature for January could rise a fair amount.
"The mean temperature is 19.85degC - that actually may go up, which is pretty significant when you get this late in the month because you have to get pretty big temperatures to shift that average temperature.
"It's going to be warm, especially next week. Next week very well could be the hottest week of the summer.
"This [heat] is difficult for lots of people."