Deluge looms before icy snap

Icicles hang off Lorenz's Cafe on the Whakapapa skifield, Mt Ruapehu, over Queen's Birthday weekend.

Brollies on agenda then blast from Antarctica will set country shivering.

An "Antarctic snap" is expected to set the country shivering later this week, but not before heavy rain sends much of the North Island reaching for raincoats and umbrellas.

It will be a wet start to the week after the Queen's Birthday holiday, MetService says, but as next weekend draws closer it will be time to pull out those winter woollies again.

WeatherWatch said the South Island was in for an "Antarctic snap", with a "pretty sudden drop in temperature", as a cold southerly flow spreads over the region.

Several heavy rain warnings start off the week for the northern half of the North Island and the upper South Island, with most of the North Island likely to have periods of rain today.

Bursts of heavy and possibly thundery rain are expected in northern and central parts today and tomorrow, with the heaviest falls likely in Nelson, the Richmond Range, Mt Taranaki, Tongariro National Park, Bay of Plenty and the far north of Gisborne.

Rainfall of between 100mm and 140mm was expected in those areas over a 12 to 27-hour period, MetService warned.

Heavy rain watches are also in place for Northland, Auckland, Waikato and the Coromandel Peninsula, Waitomo, Taumarunui, Taranaki, Marlborough and Buller today. There could also be severe gales in Auckland and Northland later tomorrow and early on Thursday.

"Over the next couple of days we have a complex low crossing over New Zealand. That low centre should pass over on Wednesday and behind the low centre we expect a southerly to push up the country," MetService meteorologist Hannah Moes said.

"So we're looking at colder temperatures ... for the South Island that will begin from [tomorrow] and ... push into the North Island on Thursday."

She said that as the low crossed the country it would bring periods of rain to most areas, but particularly those in the north and west. The southerly's approach would bring snow to low levels in the south, Ms Moes said.

On Thursday there would again be rain or showers for most places, she said, but in the South Island the skies would clear except in the far south where it was expected to snow.

WeatherWatch said a cold southerly airflow was set to spread over the lower half of the country.

"Some places can look ahead to snow flurries, though most of the worst of the weather should pass by Friday ... and most of the heavy stuff should stay where it belongs - on the skifields," the forecaster said.

Invercargill could expect 4cm of snow down to 800m by Thursday. It might be 1cm down to 300m in the afternoon before clearing.

Main centres forecast

Whangarei: Heavy rain today, easing to showers, with a fresh northerly and a high of 21C. Tomorrow will bring showers, some heavy and with a chance of thunder, northwesterlies and a high of 18C.

Auckland: Expect heavy rain today, easing to showers in the afternoon, a fresh northerly and a high of 19C. Showers tomorrow, some heavy and with a chance of thunder, northwesterlies and a high of 17C.

Hamilton: Rain today, possibly heavy, turning to showers in the afternoon, a northeast wind and a high of 18C. Expect showers tomorrow, some heavy and with a chance of thunder, northwesterlies and a high of 16C.

Tauranga: Today should bring rain, becoming heavy in the afternoon, strong northeasterlies and a high of 18C. Occasional showers tomorrow, northwesterlies and a high of 17C.

Wellington: Cloudy today with occasional rain, northerlies and a high of 17C. Tomorrow turns cloudy again with occasional rain, northerlies and a high of 15C. (Source: MetService)