A cold change is set to spear the country after a hot and humid few days - cutting more than 10C from some daytime highs.
Warm and moist air was pulled down from the subtropics to New Zealand over the weekend, leading to heavy rain and a big jump in our overnight temperatures.
MetService says this warm, moist northwest flow persists over New Zealand into the start of the week.
"That will mean more rain to western parts, and gales in the far south," it says.
"On the plus side, it also means we don't have to be digging into the firewood pile so much, as overnight temps will continue to be balmy for the time of year: mid-teens for most tonight and Monday night, and daytime highs follow the same trend: high teens and low twenties across the board Monday and Tuesday."
But on Tuesday night a cold southerly change knifes its way up the South Island, spreading into the lower North Island on Wednesday morning.
By Thursday morning it will be across all of the country with a brief area of high pressure behind it to lock in the cold at night.
A NIWA graphic video shows the wave of cold air hitting and driving the warmth back as New Zealand is plunged into single-digit temperatures.
"In the South Island temperatures will tumble the most. Here are some daytime high examples right across NZ showing the incoming change," WeatherWatch says.
- Christchurch: 22C Tuesday, 11C Wednesday
- Dunedin: 16C Tuesday, 9C Wednesday
- Gore: 19C Monday, 9C Wednesday
- Alexandra: 19C Monday, 8C Wednesday
- Timaru: 21C Tuesday, 10C Wednesday
- Wellington: 18C Tuesday, 12C Wednesday
- Napier: 23C Monday, 13C Thursday
- Auckland: 21C Tuesday, 16C Thursday
Frosty weather is also expected in the South Island as overnight lows drop below zero in the nights ahead.
"Check to see if your property is in the frost risk zone or not!" WeatherWatch warns.
