A strong moist northwest flow covers central and southern New Zealand on Thursday, while a weak ridge extends onto northern New Zealand from a high centred northeast of the country. Heavy rain is expected about the Southern Alps and the west of the South Island.

There is high confidence that warning amounts of rain will fall in central and northern Fiordland, Westland district (especially about the ranges) and the headwaters of the Otago and Canterbury lakes and rivers. There is moderate confidence of rainfall reaching warning criteria about Buller and Grey districts, and low confidence that a rain warning will also be needed for western and inland Tasman district, southern Fiordland, western Southland and Central Otago.

Additionally, for inland Canterbury, Marlborough, Wellington and Wairarapa, there is moderate confidence that the northwest winds will reach severe gale strength in exposed places.

A strong northwest flow persists over central New Zealand on Friday, with embedded fronts bringing periods of rain to central and western areas.

There is moderate confidence of rainfall amounts reaching warning criteria about western Tasman and Buller districts (including the Paparoa range), and also the Tararua Range. There is low confidence of warnable amounts of rainfall about other northern and western South Island areas from the western Marlborough Sounds and Richmond ranges to Grey District, and also for Mt Taranaki.

Additionally, there is moderate confidence that northwesterlies will reach warning strength about exposed parts of Wairarapa, Wellington and Marlborough.

A large trough of low pressure is expected to cover much of New Zealand on Saturday, with northerlies affecting the North Island and colder south or southeasterlies developing over the South Island. There considerable uncertainty regarding the areas most affected, however heavy rain could affect many parts of the country.

There is moderate confidence that northerly rainfall could reach warning criteria about Mt Taranaki, Kapiti (including the Tararua Range), Wellington, northern Marlborough and Nelson/Tasman, and moderate confidence that heavy south or southeasterly rain could reach warning criteria about eastern Marlborough, Canterbury and North Otago. There is low confidence of warnable amounts of rain about eastern Bay of Plenty, and many other areas from Waitomo to Westland and Clutha (including Dunedin).

Additionally, there is also low confidence that snowfall about inland Canterbury (and possibly North Otago) could reach warning criteria above 500 metres.

There is considerable uncertainty regarding the weather over New Zealand on Sunday, but a large area of low pressure may cover central New Zealand.

There is low confidence that heavy northerly rain could reach warning criteria about eastern Bay of Plenty and the far north of Gisborne/Tairawhiti, and also that heavy easterly or southeasterly rain could reach warning criteria about South Canterbury, North Otago, Dunedin and Clutha.

Additionally, there is low confidence that heavy snow could fall above 500 metres about South Canterbury and North Otago.