A high that is east of New Zealand is extending a ridge over the North Island for the first part of the week ahead, says a MetService spokesperson.

A front moving north over the South Island during Monday and Tuesday is expected to bring heavy rain to the west and very strong northwesterlies to the Alps and east of the South Island and southern North Island. The front should weaken late Tuesday or on Wednesday.

During Monday and Tuesday there is moderate confidence that a rainfall warning will be needed for Fiordland and Westland and the headwaters of the Canterbury and Otago lakes and rivers. There is low confidence that warning amounts of rain will fall in Buller and western Tasman Sea during Tuesday.

On Monday, there is also moderate confidence that northwest winds will reach severe gale strength in parts of Fiordland and Southland and in inland areas of Otago and Canterbury during Monday. About northern Marlborough, Wellington and Wairarapa there is low confidence that a wind warning will be needed on Monday and Tuesday due to severe gale northwesterlies.

After Tuesday, a large high over the Tasman Sea should extend a ridge onto the country where it remains for the rest of the outlook period.