Strong winds and heavy rain are lashing parts of the country with motorists warned to watch out for debris on State Highway 1 from storm surge.

An active front is forecast to move eastwards across New Zealand today, bringing heavy rain and gale-force winds for many areas. Conditions are not expected to ease until the front has passed.

Winds have already peaked at 113km/h in Wellington and the Tararua Range has been drenched with 225mm of rain in the past 24 hours.

Isolated thunderstorms are forecast to hit western regions across the South Island early this afternoon.

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The active front - currently over Fiordland - will continue to move towards the North Island from late this afternoon, however with a lower chance of thunderstorms.

Western coasts are the "main ones under firing line". MetService said this would widen as the weather system headed towards the North Island.

Heavy rain warnings had been issued for Westland, Buller, Nelson, Marlborough Sounds, Richmond Ranges, the Tararua Range and Mount Taranaki.

Watches are in place for heavy rain across Fiordland, the central North Island hill country from Taranaki across to Tongariro National Park and Waitomo, the headwaters of the Whanganui River, and the eastern ranges of Bay of Plenty.

Collingwood has seen the largest downfall, with 108mm in the past 24 hours.

MetService has reported high accumulation of rain in the ranges. Tararua Range has had 225mm in the past 24 hours.

"This will affect lower lying areas as the rain drains down out of the ranges," a Metservice spokeswoman said

"We are having very intense rain and downpours".

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Fiordland and the West Coast are under a moderate thunderstorm risk this afternoon, with expected heavy rain of 10 to 20mm per hour, hail and strong wind gusts 80-100km/h.

There is a moderate risk of thunderstorms this evening for Westport and Nelson, accompanied by localised heavy rain of 10 to 15mm per hour and strong winds of 80-100km/h.

A low thunderstorm risk has been issued across central North Island from Taranaki to Tongariro National Park and Waitomo, also the eastern ranges of Bay of Plenty.

Though the risk of thunderstorms is lower over the North Island, strong gusty winds of 90-110km/h are likely. In particular, Auckland is most likely to see gusty winds Sunday evening, along with a burst of heavy rain.

"If you see [a thunderstorm] we expect them to be very intense."

Meanwhile, many western and northern regions across the country can expect brief heavy rain and gusts of up to 110km/h.

Severe gale warnings have been issued across multiple regions. Wellington, inland Marlborough and the Sounds, and Wairarapa south of Featherston are expected to have severe gale force winds gusting 140km/h this evening.

Taranaki, Whanganui, Taihape and the Canterbury high country could expect severe gale winds of 120km/h.

Wellington had experienced the strongest winds so far, recording a gust of 113km/h.

MetService said the rest of the country could expect winds to ease off late in the afternoon and tonight.

An area of concern was along State Highway 1 between Paraparaumu and Wellington during high tide, with the combination of northwesterly winds and swells. The highest swells reported were four metres.

This watch is also for the possibility of severe gale north to northwesterly winds during Sunday over much of the North Island, from Northland to Waitomo and across to Hawke's Bay and Gisborne, also Manawatu and to the Kāpiti Coast.

Strong winds could damage trees and unsecured structures homeowners are warned to ensure trampolines are tied down.

Watches for strong winds are in place for Northland, Auckland including Great Barrier Island, Coromandel Peninsula, Waikato, Waitomo, Taumarunui and Taupo, Bay of Plenty, Gisborne, Hawke's Bay, Manawatu, Horowhenua, Kapiti Coast and Wairarapa from Featherston northwards.

Areas covered by heavy rain warnings could see rivers and streams rise rapidly and experience hazardous driving conditions.

Snow is expected late tomorrow in the Crown Ranges, Lindis Pass and along the Desert Rd.

"There is a chance of a little snow dusting."

Hazardous weather across the country on Sunday:

The worst of the weather will be found along and west of the Southern divide.
Snow above 1000m and heavy rain elsewhere.
Some flooding & slips possible across Tasman-Nelson-Marlborough.
Thunderstorms warnings across central North
Island and South Island's West Coast.
Risk of rising rivers and streams.