Weather: 'Injection of Antarctic air' to blast New Zealand, temperatures to plummet below zero

An "injection of Antarctic air" is expected this week, WeatherWatch says. Photo credit: Getty Images

Southerners may be in for a few cold mornings this week as a "powerful high" hits New Zealand, and forecasters are urging people to be vigilant for incoming big waves.

WeatherWatch said the South Island can expect frosts and an "injection of Antarctic air" this week before conditions become milder at the weekend.

Southwest winds will drive that cooler air, according to NIWA.

"A southwesterly airflow will keep things on the cooler side for about a week," NIWA said.

"Conditions will likely turn warmer by the end of the month."

Large waves were also possible for some parts of the country this week.

"These swell waves are being generated by a large area of southwest gales that is blowing over the Southern Ocean between New Zealand and Antarctica," MetService meteorologist Peter Little said. "These large swell waves have the potential to cause coastal inundation and erosion of our shores, especially around high tide.

"Beach users and boaties are advised to exercise caution as these unusually high swell waves will be hazardous."

Freezing mornings for some

Some South Islanders will wake up to temperatures at 0C and below this week.

Wanaka will drop to 0C overnight Wednesday and Thursday, and Christchurch will be at -1C on Thursday morning.

Little said some inland areas of both the South and North Islands could fall as low as -3C.

He said there may also be some snowfall at high levels.

"A weak cold front that is forecast to move northwards over the South Island on Wednesday may provide another dusting of snow down to 600 metres over southern New Zealand, which may affect a few higher roads. 

"With only one week to go until the start of winter, it's unusual that we're still waiting for the first big snow dump of the year."