Much of the country can expect rain at some point today - with heavier rainfalls set to impact those in the south.

A rain band crosses the North Island today and early tomorrow; bringing with it rainy periods this evening and tonight to areas including Auckland, Whāngārei, Tauranga, Hastings, New Plymouth and Wellington.

Aucklanders are in for a 20C high and overnight low of 14C.

Cloudy conditions will increase gradually today and there will be patchy rain periods in the City of Sails tonight.

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Those preparing for the ASB Auckland Marathon on Sunday will be happy to hear conditions are set to be "reasonable" for outside activity.

"There is a brief break in the weather during the weekend, which lasts until Sunday afternoon for the North Island," MetService meteorologist Andrew James said.

"This brings reasonable conditions for the Auckland marathon and runners should expect cloud cover and a high of around 18C."

The majority of places in the North Island are in for some warm temperatures today.

Highs of between 18C to 20C are forecast in most places in the upper North Island, at least, including in Kaitaia and Northland, Tauranga and Hastings.

Today's rain band is connected to a low pressure system affecting the country at the moment - particularly the West Coast and the western North Island.

Colder air coming in around the Southern Alps will also bring snow to the area, WeatherWatch said.

"Eastern areas have mild winds and above normal temperatures this weekend," a spokesman said.

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"Eastern Northland, Hawke's Bay, Gisborne, Canterbury, Marlborough and parts of Otago all have day-time highs around the late teens and early 20s this weekend."

Strong winds are due to hit both the North and South islands ahead of a front due to arrive from the Tasman Sea on Sunday.

The strongest gusts are expected in Wellington, in and around Wairarapa and the Marlborough Sounds.

HEAVY RAIN WARNINGS:
The MetService has issued a number of severe weather warnings - mainly for those in the South Island - and is warning people to stay alert.

"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."

Heavy rain warnings are in place for areas including Nelson west of Motueka and Buller, where rain accumulations of between 90mm to 140mm of rain are expected throughout today and through to 5am tomorrow.

People in the area are also being told there is also a possibility of thunderstorms starting tonight.

Locals in and around Westland from Fox Glacier northwards should also be prepared for a deluge throughout today until about 11pm.

"Expect a further 80 to 110mm of rain to accumulate about the ranges - with 40mm to 60mm nearer the coast."

Members of the public are reminded to stay alert and keep a close eye on weather updates. Another severe weather update is expected later tonight.