New Zealand weather: Damaging winds, heavy rain, 13-metre waves forecasted as storm sets in this week

New Zealand is set to be battered by 130km/h winds, heavy rain and waves of up to 13 metres, Weather Watch has warned, with a powerful storm set to make landfall this week.

The wintery conditions will arrive on Tuesday before dying out in time for the weekend.

Most parts of the country will be affected in some way, with the South Island likely to bear the brunt of the chaotic weather. MetService has issued a severe weather watch for both heavy rain and strong winds.

Gusts will be at their most severe from Tuesday afternoon through Wednesday. The capital is expected to live up to its 'Windy Welly' moniker, with gales of up to 130km/h possible in the city and 150km/h in the ranges above.

Violent, localised winds are also anticipated in Stewart Island, the lower South Island and the Southern Alps on Tuesday and Wednesday as a chilly southerly kicks into gear.

The Southern Alps will get heavy snow, with 1.5 metres expected near the peaks - described as "an exceptional amount" for this time of year by forecasters - and heavy rain is anticipated for the West Coast.

Weather Watch warns conditions over the next few days could be so severe that travel plans - be they by air, road or sea - may be impacted. Electric utility company Vector hasn't yet made preparations for widespread power outages, but is monitoring reports.

Waves at the country's west coast beaches are already beginning to grow, with heights of five metres expected in the South Island later on Monday afternoon.

By Tuesday night, the forecaster says, wave heights will still be "dramatically increasing" - and may make a dip in the ocean too dangerous for swimmers and surfers alike.

"The entire southern half of the West Coast will have waves crashing in coastal areas of 12 to 13 metres and more populated beaches like Hokitika and Greymouth have waves of 7 to 10 metres developing overnight Tuesday and into Wednesday morning," Weather Watch says.

"While the eastern North Island does have much calmer seas in the east it is very important to highlight the fact winds will be blowing from land out to sea. That means those on floatable devices have an increased chance of being blown out to sea even if the sea itself is fairly calm.

"Please take extreme care this week in the water and if in doubt, please, simply stay out."

MetService meteorologist Peter Little says the huge swell isn't just a danger to swimmers - it's likely to cause damage to our coastline, too.

"In addition to the large size of the swell waves, the long period of 16 to 18 seconds between them means the swells will contain a lot of energy and have the potential to cause coastal erosion," he explained.

While the West Coast will be bombarded with massive downpours and strong winds, northern and eastern parts of the country will remain mostly dry throughout the week - and some areas will see scorching summer temperatures too.

The eastern North Island could reach 30C on Tuesday - but it's one of only a few places that will enjoy the seasonal warmth this week.

Temperatures will plummet by more than 10C across large swathes of the South Island, with parts of Southland set for a high of just 10C on Wednesday.

Milford Sound, Queenstown and Dunedin are also set for a cold shift later this week.