Heavy rain and thunderstorms are set to batter parts of the country today as a front arrives from the Tasman Sea.

The South Island's West Coast would cop the worst of it, with up to 200mm of rain forecast in the ranges.

Parts of the lower North Island could see some showers too ahead of a wet end to the week.

Auckland would escape most of the wild weather today with mostly fine conditions, northerlies and a high of 22C. Tomorrow, heavy rain was due to set in from mid-afternoon.

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MetService meteorologist Kyle Lee said worst-affected today would be Westland south of Otira on the South Island's West Coast. A severe weather warning was in place for many areas, with 150-200mm of rain forecast to fall about the ranges today, and 80-100mm by the coast.

The south Westland area, still recovering from a deluge two weeks ago that saw more than a metre of rain places, would also be affected.

Around Franz Josef town, where urgent repairs are under way on the Waiho River bridge connecting the road south of the town, 40-45mm of rain had fallen overnight, with much more forecast today.

MetService Severe Weather Update: April 10th

Lee said the worst of the weather was forecast this afternoon, with a high risk of thunderstorms for Fiordland and southern Westland, with potential associated downpours of 20-30mm in an hour.

There was also a severe rain warning for the Otago river and lake headwaters.

Aside from that, Wednesday was looking mostly fine for the country, Lee said.

The east coast of the South Island would see a southerly change, while the lower North Island could see some showers as the front crept up the country.

On Thursday, the front would reach the North Island - moving north across central and northern areas, bringing rain with some heavy falls.

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It would be followed by cold southerlies, with gales affecting the east coast of the North Island on Friday.

A ridge was expected to spread onto the South Island from the Tasman Sea on Friday and gradually extend northwards on Saturday, bringing a fine start to the weekend for most.

A weak cold front should move north over the South Island on Sunday.

Today's weather

Whangārei

Fine, but some morning cloud. Light winds. 23C high, 13C overnight.

Auckland

Fine, apart from some morning cloud. Northerly breezes. 22C high, 14C overnight.

Hamilton

Cloudy periods. Chance afternoon shower. Northwest breezes. 22C high, 11C overnight.

Tauranga

Fine. Light winds, afternoon northerlies. 23C high, 13C overnight.

New Plymouth Cloudy periods. A few showers. Northwesterlies. 21C high, 16C overnight.

Napier Fine. Light winds, afternoon northerlies. 24C high, 13C overnight.

Whanganui Fine, but some morning and evening cloud. Light winds, afternoon northwesterlies. 23C high, 14C overnight.

Wellington Cloudy periods. A few spots of light rain. Northerlies, strong from afternoon. 20C high, 15C overnight.

Nelson Fine at first. Cloud increasing afternoon and chance shower. Northerlies picking up. 21C high, 15C overnight.

Christchurch Cloudy periods. Rain developing overnight as gusty northerlies change strong southerly. 25C high, 11C overnight.

Dunedin Cloudy. Rain developing around midday, briefly heavy, as gusty northerlies change strong southerly, easing at night. 21C high, 10C overnight.