Whangarei is forecast to hit 20C and Auckland 18C.
Temperatures across Waikato and the Bay of Plenty will be in the late teens, and the East Coast is also in for a fine and sunny day with a high of 20C in Napier.
The South Island's east coast is in for a bit of the same, with fine weather and warm northwesterlies pumping temperatures to 18C-19C in Nelson, Christchurch and Dunedin.
That same westerly flow will bring cloud and showers to the West Coast of the South Island, but temperatures there will also be in the late teens.
The main weather for today will be around the bottom of the South Island.
A cold front that moved east across the south of the South Island overnight is bringing severe westerly gales to exposed parts of coastal Southland and Clutha, including Stewart Island. Severe gales may reach 120km/h through to 4pm today.
This morning there is also a low risk of thunderstorms in Fiordland and southern Southland, with potential for heavy rain and strong winds.
Tomorrow a cold front, preceded by strong and moist northwesterlies, is moving up the South Island. Winds could reach severe gale in the lower and central South Island, and rain could get heavy through Fiordland and Westland.
The front should weaken over central New Zealand early Wednesday as a ridge of high pressure spreads over the country from the west.
The ridge should persist over the country on Thursday, then move eastwards on Friday as a trough of low pressure approaches New Zealand from the Tasman Sea, bringing an end to the settled weather.
"At this stage, that low looks to impact the country over part of the weekend," Zachar said.
Today's weather
Whangarei Mainly fine, but one or two light showers in the morning. Southwesterly. 20C high, 10C overnight.
Auckland Mainly fine, but one or two light showers in the morning. Southwesterly. 18C high, 13C overnight.
Hamilton Chance morning shower, then a fine day. Southwesterlies. 18C high, 7C overnight.
Tauranga
Fine. Southwesterly breezes. 19C high, 10C overnight.
New Plymouth Morning cloud clearing to a fine day. Southwest breezes. 17C high, 11C overnight.
Napier Fine with light winds. 20C high, 8C overnight.
Wellington A fine day. Northerlies developing. 16C high, 13C overnight.
Nelson A fine day. Northwesterlies developing. 18C high, 11C overnight.
Christchurch Fine with high cloud at times. Northwesterlies strengthening. 19C high, 7C overnight.
Dunedin Fine with high cloud at times. Northwesterlies. 18C high, 10C overnight.