A west to southwest flow is expected to cover the northern and central New Zealand on Tuesday, says a MetService spokeserson.

A northwesterly flow will develop over the south of the South Island, but there is minimal risk of severe weather affecting New Zealand.

On Wednesday, August 7, frontal rain-bands embedded within a strengthening northwest flow will move onto the South Island, while a weakening ridge of high pressure will cover the North Island.

"There is low confidence that rainfall about Fiordland and Southern Westland will reach warning criteria, and low confidence that northwesterly winds could reach severe gale about southern Fiordland, Southland and exposed parts of mainland Southland," says a MetService spokesperson.

"A front should move northwards over the South Island on Thursday, while a second rain-band in the north Tasman Sea moves onto the North Island.

"At this stage there is uncertainty regarding the movement and intensity of these rain-bands.

There is therefore low confidence that rainfall could reach warning criteria about western Tasman, Buller, Westland and Mount Taranaki on Thursday."

MetService says there is considerable uncertainty regarding the weather over New Zealand on Friday, with a low and associated rain-band possibly moving over or lying near the North Island.

"There is currently a minimal risk of severe weather affecting New Zealand on Friday, however given the uncertainty, it is possible this risk may change over the next few days."