By early evening there could be light showers in Auckland, but it will still be warm, with MetService predicting it will be 20C in Auckland at midnight and dropping to 17C at about 3am.
"At night cloud traps in the heat, so we are looking at some quite pleasant temperatures overnight," MetService shift meteorologist Robb Kerr said.
Kerr said the North Island was the best place to be. "The further north and the further east you can go, the better you will be."
His top picks included Masterton, Hawke's Bay, Gisborne, Tauranga, Whakatane, Whitianga and Whangarei. Weather conditions were similar, if not better for New Year's Day.
Taumarunui is expected to reach 28C, Thames and Whitianga 27C and Auckland 24C. New Plymouth would be one of the coldest places to be in the North Island with a high of 23C.
"Really across the North Island it's looking mid to high-20s."
The South Island will be wetter, with rain forecast for western areas - including Hokitika, Westport and Greymouth - on both New Year's Eve and Day.
There is currently a severe weather watch on the West Coast of the South Island and while it would lift by tomorrow, heavy rain is still expected in the western areas.
However, other parts of the South Island will bask in warmer than average temperatures on New Year's day, with Queenstown reaching 27C, Invercargill 25C and Gore 24C.
"It's a similar story across the South Island. Hokitika is the coldest and despite the rain is 21C."
Most of the North Island would end 2018 and start 2019 with temperatures between 25C and 28C - 3C higher than today.
Forecast:
Whangarei:
New Year's Eve - Partly cloudy, chance afternoon shower. Southwesterlies developing afternoon. High 25C.
New Year's Day - Partly cloudy, chance afternoon shower. Southwesterly breezes. High 26C.
Auckland:
New Year's Eve - Cloudy periods, with isolated afternoon showers. Southwesterlies. High 24C.
New Year's Day - Cloudy periods. Southwest breezes. High 24C.
Hamilton:
New Year's Eve - Cloudy periods, with long sunny spells in the afternoon. Westerly breezes. 24C.
New Year's Day - Cloudy periods, with a chance of a shower. Westerly breezes. High 26C.
Tauranga:
New Year's Eve - Partly cloudy. Westerly breezes dying out. High 27C.
New Year's Day - Partly cloudy. Light winds and sea breezes. High 27C.
Wellington:
New Year's Eve - Mostly cloudy, but sunny spells this afternoon. Strong northerlies. High 22C.
New Year's Day - Partly cloudy. Northerlies developing afternoon. High 23C.
Christchurch:
New Year's Eve - Cloudy periods, chance afternoon shower. Northeast breezes. High 19C.
New Year's Day - Fine. Northeasterly. High 25C.
Dunedin:
New Year's Eve - Occasional rain developing morning. Northeast breezes. High 18C.
New Year's Day - Morning cloud then mainly fine apart from chance shower. Northerlies. High 23C.
Source: MetService