Frosts are forecast for both islands over the next couple of nights as New Zealand is hit by a sharp cool-down.
A southerly flow covers the country on Tuesday, meaning colder than average weather - especially for the North Island.
WeatherWatch says frosts will make it as far north as Waikato and even sheltered parts of Auckland over the next couple of nights.
"The temperatures tonight - they are dropping. We've got colder than average weather in a number of places going right up to Northland. So it'll be 4-8C below average up there," WeatherWatch CEO and head forecaster Philip Duncan says on YouTube.
This means overnight lows of 5C and 6C for many places in the North Island. The central spine of the South Island will also go below freezing.
On Wednesday a high rolls in and works with the southerly to make Wednesday night cold as well.
"So with the southerly and the high it means that tomorrow night is also cold - more so in the North Island right all the way up to Northland," Duncan says.
The North Island is forecast to see overnight lows of 4C, 5C and 6C in many places.
"We might be seeing frosts you know up into Waikato - I'd keep a close eye on this so we've got a cold night coming up, that's tomorrow night going into Thursday morning," Duncan says.
However as early as Thursday afternoon the warm nor'westers will kick back in for New Zealand.
"By Thursday night milder air moves in with overnight lows in Southland over 4C above normal by Friday morning. That milder air then moves northwards covering all of NZ this weekend," WeatherWatch says.
"It won't last too long though. By Monday next week a wintry southerly returns to the country."