MetService has issued a Severe Weather Outlook for Monday through to Thursday.

"During Monday a northwest flow over the South Island and southern North Island should strengthen as a low moves eastwards across the southern Tasman Sea,' says a MetService spokesperson.

"The low should cross over, or just to the south of, the South Island on Tuesday.

"There is likely to be gale west to northwest winds in many places and heavy rain about the west of the South Island and southern North Island."

MetService says there is moderate confidence that a rainfall warning will be needed in Fiordland during Monday and Tuesday, while for Westland, there is low confidence of warning amounts of rain on Monday but moderate confidence that Tuesday will have a rainfall warning for the area.

There is low confidence that a rain warning will be needed in Buller and the Canterbury high-country on Tuesday and about the Tararua Range on Tuesday and Wednesday.

There is low confidence that west to northwest winds could rise to severe gale in exposed places in the east of New Zealand from Southland to Wairarapa, including Wellington during Monday with moderate confidence that a wind warning will be needed in these areas for Tuesday.

"Note, late Tuesday in the south of the South Island, the flow should turn west to southwest behind the front, but could still be severe gale in exposed places."

Overnight Tuesday to Wednesday, snow may fall to reasonably low levels in the south of the South Island, and there is low confidence that a snow warning will be issued for inland areas of Southland, Otago and South Canterbury for heavy snow above about 500 metres.

On Wednesday, winds turn southwest over the country as the low moves away.

There is low confidence that severe gale westerlies will be experienced in Central Hawke's Bay on Tuesday and Wednesday and that severe gale southwesterlies will affect Northland and Auckland on Wednesday.

The southwest flow should ease over the country on Thursday as a large high over the Tasman Sea moves closer to New Zealand.