Parts of the lower South Island are sweltering with temperatures hitting the high 20s.
Invercargill, Balclutha and Ashburton were 29 degrees today with other eastern areas in the mid to high 20s.
Cookin' across the South Island today ♨️— NIWA Weather (@NiwaWeather) December 29, 2018
Balclutha reached 29.6°C, good for the 5th warmest December temperature on record in the town. pic.twitter.com/z4zNgXfcUe
MetService meteorologist Rob Kerr said a warm north-west flow was behind the hot weather, which should continue into tomorrow.
"Across the South Island tomorrow we could see even warmer temperatures, we are looking at the possibility of 30 degrees for the likes of Christchurch and Blenheim, and mid to high 20s for the eastern South Island, from Gore all the way up to ... Nelson," he said.
All North Island stations recorded maximum temperatures above 20C today. However, thanks to the hot air from Australian being carried over the Tasman Sea to Southland, Otago and Canterbury, Invercargill recorded 29C as did Ashburton. On the west coast Haast only managed 16C. ^AB pic.twitter.com/CpK18B0MI6— MetService (@MetService) December 29, 2018
It will be a bit windy through the lower North Island, so the temperatures won't be quite as high as those in parts of the South Island.
But eastern areas, like Napier and Gisborne, could hit 28 or 29, Mr Kerr said.
Australia shipping some of its heat to Aotearoa! ️— NIWA Weather (@NiwaWeather) December 28, 2018
The end to 2018 and start to 2019 will be warmer than average for much of NZ thanks to a trans-Tasman air flow. pic.twitter.com/aXOAUpprvL
The weather should be fine and settled over the upper North Island, with highs in the mid-20s.
Mr Kerr said it was looking good across much of the country heading into New Year's Eve celebrations.
Meanwhile, a severe weather watch is in place for heavy rain in Fiordland and southern Westland.