Temperatures range in the mid-teens in the North Island, while parts of the South Island will see high single-digit temperatures.
MetService forecaster Allister Gorman said: "By the middle of [today], things should have eased right back and [tomorrow] and Monday are looking quite good days for a winter school holiday."
A front was forecast to move over Auckland towards Northland overnight, meaning showers last night and possibly this morning.
"The main trouble in the South Island [today], if anyone is out early, they'll just have to watch for frosty conditions and there might be a little bit of black ice on a couple of roads," Gorman said.
Police earlier closed off State Highway 2, north of Katikati, due to flooding; while Southern Police urged motorists to drive carefully after icy roads led to a number of incidents of vehicles sliding.
There was a dramatic rescue after a truck plunged at least 50m into the Manawatu Gorge yesterday morning. One person was winched from the truck cab while the second was helped from near the truck, the Philips Search and Rescue Trust said. The truck's occupants, a man and woman aged in their 40s, were taken to Palmerston North Hospital. Three of their rescuers were also taken to hospital, but were not admitted.
A rain watch was also in place over the Tararua and wider Wairarapa areas last night, as well as for the Bay of Plenty.
Gorman said late yesterday: "The Coromandel's still got some flooded roads ... . "There's still some cleaning up to do probably around the Coromandel to Auckland area."
Today's forecast
Whangarei: 16C high, cloudy periods and a few showers. Strong southeasterly winds.
Auckland: 15C, fine spells, strong southeasterlies.
Tauranga: 15C, mostly sunny.
Hamilton: 14C, sunny, gusty southeasterlies.
Gisborne: 13C, rain easing to showers in morning. Strong southeasterlies easing.
Coromandel: 14C, showers clearing before dawn then fine spells. Strong southeasterlies.
Wellington: 11C, becoming fine. Strong southerlies easing.
Christchurch: 10C, becomes fine in morning, light winds.
Dunedin: 9C, sunny, high cloud. Morning frosts.