Today's top temperature was recorded at Lake Pukaki in the Canterbury High Country, where it hit 32C by 2pm.
In the South, Christchurch experienced 25C but Dunedin could only manage a peak of 18C early in the day before dropping to a less than summery 11C.
MetService says a high-pressure system and a drift of warm, humid air over the country has been spreading moisture over the islands and could spell rain on Christmas Day.
Forecast from Friday through Sunday
On Friday, showers could appear in western and southern areas of the South Island and Wellington could also see patchy morning drizzle.
Dunedin has showers forecast to develop in the afternoon accompanied by southerlies.
In Invercargill the big day is forecast to be partly cloudy with a few showers developing.
Queenstown's forecast is kinder with fine weather and a predicted high of 25C.
Auckland, meanwhile, has a mostly cloudy Friday with some northeasterly winds developing in the morning, but still a 25C high and an 18C low.
Christchurch should also be cloudy with a 20C high.
MetService said Saturday would be when rain becomes more widespread with a flow of moisture from the northwest hitting the country from early morning. The City of Sails should dodge this, seeing another partly cloudy 25C day.
The moisture would continue to roll over the country on Sunday with MetService warning of the potential for a few heavy showers in the North Island.
Showers will likely fall in Auckland, but as the city is set to remain at 25C, the mugginess was unlikely to ease.
Forecast from Chrismas Day to new year
MetService said the wet conditions of the weekend would linger until Christmas Day and beyond, although, it would be spotty across the country with passing showers forecast for some and heavy showers for others.
Eastern areas of the North and South Islands had the highest chance of escaping the rain on Monday.
MetService meteorologist Lewis Ferris said: “Those hoping to have a day at the beach on Christmas Day will need to keep a close eye on the forecast, and it’s recommended to have a wet weather plan in case those showers do happen to turn up.”
After Christmas, the final days of the year should be equally warm and muggy, especially in Auckland where daily highs weren’t expected to drop below 25C and lows wouldn’t go below 18C.
