MetService says a northwesterly flow will be affecting northern and central New Zealand on Monday, August 26, with a series of embedded fronts affecting the country, bringing rain to many places.

"There is moderate confidence that rainfall amounts will reach warning criteria about the Buller and Grey Districts, and low confidence for northern Westland District, Tasman/Nelson, northern Marlborough, Kapiti and Horowhenua (including the Tararua ranges), and also Mt Taranaki," says a MetService spokesperson.

On Tuesday, a north or northwesterly flow with embedded fronts will be affecting the country. 

"There is low confidence that heavy rain warnings will be required for the west of the South Island from southern Westland northwards to western Tasman, including the Southern Alps, and also for the Tararua ranges and the central North Island from Taranaki across to eastern Bay of Plenty.

"However, there is moderate confidence that rainfall amounts will reach warning criteria on Mt Taranaki."

MetService says in addition, there is low confidence of severe northwest gales for northern Marlborough, Wellington, Wairarapa and Central Hawke's Bay.

A strengthening northwest flow is expected to spread over central and southern New Zealand on Wednesday, with embedded fronts bringing rain to the western South Island.

"There is low confidence that rainfall amounts could reach warning criteria about the Westland District, Fiordland and the Southern Alps.

"There is also low confidence the northwesterly winds could reach severe gale about exposed eastern and southern areas from the Tararua District to Southland and southern Fiordland." 

A strong northwest flow should cover New Zealand for a time on Thursday with embedded fronts moving over the country.

"There is moderate confidence that rainfall amounts will reach warning criteria about western South Island areas from Kahurangi National Park to Fiordland, including about the Canterbury and Otago headwaters near the main divide.

"There is also low confidence of warnable rainfall amounts about remaining parts of Tasman/Nelson. northern Marlborough, the Tararua ranges, and the high ground of northern Taranaki, southern Waitomo, Taumarunui and Tongariro National Park.

"Additionally, there is moderate confidence that northwesterly winds could reach severe gale about Wellington, Wairarapa and the Tararua District, and low confidence of severe gales about other eastern areas and southern areas from Gisborne/Tairawhiti to Southland and Fiordland, however the confidence level for these areas may increase closer to the time."