North Islanders should rug up and turn their electric blankets on tonight as overnight lows drop by as much as 7C in some areas.
Wellington, Auckland and Hamilton are in for a chilly one as unseasonably warm nights make way for a more typical winter temperature tonight.
Cloud in the east of the North Island would keep temperatures in the area from dropping quite so dramatically, said Metservice meteorologist Kyle Lee, but in the lower and central parts of the island clear overnight conditions and light winds meant a lot of heat would be lost.
"The rest of the country's getting pretty low."
Auckland and Wellington's overnight lows were both forecast to drop by 4C tonight to 4C and 5C respectively.
In Hamilton the low would dip to -2C, a drop of 7C compared to last night, Mr Lee said.
In the South Island cold nights are old news but further north tonight might feel especially frosty.
"We've had warmish spell so it feels a bit colder but it's actually average [for this time of year]."
Down south, parts of the high country would reach lows of -4 to -5C and Christchurch could expect a low of -2C.
The cold snap in the North Island follows a record warm period this year, with the hottest first six months of the year recorded by NIWA since records began.
Overnight lows and highs for tomorrow:
low of 4C, high of 15C tomorrow.
low of 4C, high of 14C tomorrow.
low of -2C, high of 13C tomorrow.
low of -1C, high of 11C tomorrow.
low of 5C, high of 14C tomorrow.
low of -2C, high of 12C tomorrow.
low of -1C, high of 12C tomorrow.
low of 13C, high of 11C tomorrow.