Sunshine bathes most of the country this morning, before a storm brewing over the Tasman arrives this evening.

A ridge of high pressure brings a fine start to the day for most of the country, MetService meteorologist Nick Zachar said.

Auckland is in for a mostly dry day, with just a few patches of cloud and a high of 20C.

Similar weather is forecast throughout the North Island, apart from the odd shower around Wellington.

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The South Island too will have a pleasant start to the day, especially in eastern areas where fine weather is forecast for Nelson, Christchurch and Dunedin and highs will be in the late teens to early 20s.

That will all start to change this afternoon, when a complex low developing over the north Tasman Sea hits the upper North Island, and a couple of cold fronts move over the South Island.

The low is expected to spread rain and easterlies over the North Island and upper South Island tomorrow, causing the front to stall over central New Zealand for a time.

Rain will set in about Northland this evening and spread to Auckland by late tonight.

The rain is set to turn heavy tomorrow and remain through Sunday.

More than 50-100mm in 24 hours may fall about Northland, Auckland, Coromandel Peninsula, Bay of Plenty and Rotorua from Saturday to Sunday.

Heavy rain is possible about Hawke's Bay and Gisborne from Sunday to Monday.

The cold fronts moving up the South Island today will turn warm northerlies to cold southerlies, spreading rain over most of the island.

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Heavy rain is also possible about Nelson, Wellington and the Marlborough Sounds on Saturday.

Although there was still some uncertainty about exactly where the low would hit the hardest, the North Island was expected to bear the brunt, Zachar said.

"Northland seems to be getting the brunt tonight and Saturday, then Auckland will see some rainfall tomorrow, but it is hard to tell exactly where with these lows.

"However the easterly flow over the North Island will drag rainfall into many locations, from north of Christchurch through central and upper parts of the country.

"The South Island looks to escape the heaviest rain, but some areas are in for a wet weekend."

MetService will issue severe weather watches and warnings this morning.

On Sunday the severe weather looks to ease over most of the country, except the upper North Island.

"On Monday there will still be showers in parts of the North Island, and more rainfall in the lower South Island as another front moves in," Zachar said.

A southerly flow is forecast to move over the country from Monday and Tuesday and into next week, bringing slightly more settled weather.

However, it is unlikely to last.

"We are in for a fairly active week, with a few fronts and southerly systems," Zachar said.

"There will be a few ridges in between those with fine periods, but it will be a very changeable period."

Today's weather

Whangarei

Often cloudy. A few evening showers. Northeasterlies. 21C high, 17C overnight.

Auckland Often cloudy. Isolated evening showers. Northeasterlies. 20C high, 16C overnight.

Hamilton Cloudy at times. Northeast breezes. 19C high, 13C overnight.

Tauranga Mostly cloudy. Few showers from afternoon. Northeasterlies. 20C high, 15C overnight.

New Plymouth Cloudy at times. Northerlies. 18C high, 14C overnight.

Napier Fine, evening cloud. Northeast breezes. 21C high, 12C overnight.

Wellington​ Cloudy at times. Could get a light shower, especially in the north. Brisk northerlies. 17C high, 12C overnight.

Nelson​ Fine with high cloud. A few showers developing this evening. Northerlies developing this morning. 17C high, 12C overnight.

Christchurch​ Fine, high cloud. Northerlies. 20C high, 8C overnight.

Dunedin​ Cloudy. Rain developing this afternoon as northeasterlies change southwest. 17C high, 9C overnight.