MetService says 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 during the second half of the day about the Westland District, Fiordland and the Southern Alps," says a MetService spokesperson

"There is moderate confidence the northwesterly winds could reach severe gale at the same time about exposed eastern and southern South Island areas from inland Canterbury to Southland and southern Fiordland. The risk of severe northwest gales for northern Marlborough, Wellington, Wairarapa and the Tararua District is considered low."

On Thursday, August 29, a strong northwest flow is expected to cover New Zealand for a time 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 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, the high ground of northern Taranaki, Waitomo, Taumarunui and Tongariro National Park, and eastern Bay of Plenty."

MetService says, additionally, there is moderate confidence that northwesterly winds could reach severe gale about inland Canterbury and southern Marlborough, the Marlborough Sounds, 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.

On Friday, a westerly flow will cover New Zealand, but this will tend northwest and strengthen over the southern South Island later in the day as a front in the Tasman Sea approaches the country.

Rain is expected to set in to Fiordland late on Friday, but the risk of warning amounts currently appears very low. There is low confidence that north to north winds could reach severe gale about exposed parts of southern Fiordland, western Southland and Stewart Island late in the day.

On Saturday, a front is forecast to move over southern and central New Zealand, preceded by a strong north to northwest flow.

"There is low confidence in warning amounts of rain for western areas of the South Island from Fiordland to Tasman/Nelson, including the Canterbury and Otago headwaters

"There is low confidence of severe north to northwest gales in exposed parts of southern Fiordland, western Southland, inland Otago, Canterbury, Marlborough, the Marlborough Sounds, Wellington and southern Wairarapa."