Snow, heavy rain and strong wind forecast in a southerly change to hit New Zealand

It's been a warm start to the week with some some areas reaching almost 30 degrees on Monday, but come Wednesday, that's likely to have all changed.

MetService is forecasting an abrupt midweek plunge in temperatures after Napier, Wairarapa and Masterton broke local temperature records for May.

A cold southerly change is expected to first hit the country this morning before moving north, bringing with it rain and snow.

MetService meteorologist Alwyn Bakker said some places in the South Island would see a 10 degree drop in temperature.

"In particular, Christchurch is expected to reach 24C on Tuesday, just ahead of the change, but only 11C on Wednesday," Bakker said.

As the southerly change moved north it was likely to bring snow to parts of the South Island above 600 metres in Southland, Dunedin, and the Southern Lakes from Tuesday afternoon, and to 700m at night in the Canterbury high country, MetService said.

The daytime temperature change would not be so dramatic for the North Island, but overnight temperatures in Auckland would going from 16C on Tuesday night to 8C on Wednesday night.

MetService had a number of warnings in place ahead of the incoming change.

A heavy rain warning was in place for Westland ranges and a strong wind warning in place for Wellington.

There were also heavy rain watches in place for Mount Taranaki, the ranges west of Nelson, the Tararua and Buller ranges, Canterbury headwaters and parts of Fiordland.

Marlborough, parts of the Canterbury high country and the Wairarapa were subject to a strong wind watch.

Road snowfall warnings had been issued for Lewis Pass, Arthur's Pass, Porters Pass, Lindis Pass, the Crown Range Road and Milford Road for parts of overnight Tuesday and Wednesday morning.

Bakker advised people to check the MetService website to keep up to date with the latest forecasts.

"We may upgrade parts of the watches to orange warnings or add further areas as the situation develops."

The MetService severe weather outlook said: "On Wednesday, a front moves northwards over the North Island bringing about a cool and unsettled southerly change, while the southerly flow across the South Island should ease as a ridge of high pressure builds across the Island.

"The southerly flow over the North Island should then ease on Thursday and the ridge should spread over the entire country. The ridge should begin to move away to the east later on Friday and early Saturday, ahead of a front approaching from the west. "

NIWA meteorologist Chris Brandolino told Morning Report the southerly change would hit Southland this morning.

"There's a streak of cloud, moisture ahead of that. So ahead of that southerly change there will be rain, which is good because we could use the rain for a lot of the country.

"So rain along a lot of the West Coast of the South Island today, a bit will spill over to Canterbury where it is really needed and then we will get some showers, maybe some thunderstorms across the North Island about this time tomorrow...

"There will be snow getting close to maybe 500-600 metres above sea level."

While further southerly changes were expected, they would not be as frequent or long lasting and they would not define winter, Brandolino said.