Muggy nights are on the way, but temperatures will soon plunge as heavy rain and severe gales sweep across the country. 

The wild weather change is set to come into force from today for Fiordland and Friday for much of New Zealand. 

MetService meteorologist Michael Pawley told the Herald a moist air mass pushing down on the country will bring sweaty overnight temperatures. 

“The overnight temperatures we’re seeing are quite warm. Places like Auckland will be having a minimum of 20C [overnight Thursday and Friday],” Pawley said. 

MetService earlier described the upcoming heat as “uncomfortably hot”. 

Pawley said once the front crosses over the country, there will be low pressure developing to the east of New Zealand. 

“That’s going to be dragging some more southerly winds. So that’ll be cooling the temperatures down into the weekend,” he said. 

For example, Masterton is forecast to drop to a high of 18C on Sunday from Friday’s sweaty high of 29C. 

‘Heavy rain and severe gales’ 

Pawley said a front is set to cross the South Island, causing rain to develop in Fiordland from tomorrow. 

“On Friday, that will push across the South Island as well, bringing a period of heavy rain and strong winds. 

“That’s essentially moving up the South Island at the same time as a trough over the northern Tasman Sea moves across the North Island,” he said. 

Pawley said once the Friday rain has crossed, a low developing up the east of the country will bring a risk of heavy rain, and severe gale southerlies. 

“There’s still a lot of uncertainty there with the position of that, and that will dictate which areas feel those impacts the most,” he said. 

At this stage, the eastern parts of the North Island are forecast to be hit the worst. 

Pawley said MetService has a moderate confidence that the rain and wind will reach warning criteria for some eastern parts of the North Island.