An active trough from over the Tasman Sea is expected to move over the South Island on Tuesday.

This trough is expected to then move over the North Island late on Tuesday and during Wednesday.

"There is low confidence that rainfall in Westland, Buller and the west of the Tasman District on Tuesday will reach warning amounts, while for the ranges of the lower North Island for late Tuesday and early Wednesday there is also low confidence that rainfall will reach warning amounts," says a MetService spokesperson.

"Additionally, northwest winds are likely to be strong or gale for a time across parts of southern and central New Zealand, and there is low confidence for severe northwest gales about northern Marlborough, Wellington and Wairarapa late Tuesday and early Wednesday."

MetService says later on Wednesday, northwest winds will start to strengthen again over southern and central New Zealand as a front crosses the Tasman Sea.

This will move onto Fiordland with rain increasing there.

"And there is low confidence that rainfall in Fiordland will reach warning thresholds late Wednesday and early Thursday."

The front moves north over the South Island and lower half of the North Island during Thursday, and over the remainder of the North Island on Friday.

"There is an associated moderate confidence for warning amounts of heavy rain in Westland, Buller, and the headwaters of the Otago and Canterbury lakes and rivers.

"While there is low confidence for warning amounts of heavy rain in the west of the Tasman District on Thursday, and the ranges of the lower North Island overnight Thursday into Friday."

MetService says with respect to the possibility of northwesterly winds becoming severe gale on Thursday, there is low confidence for eastern areas of the South Island from Southland to Canterbury on Thursday. 

"And for central areas of New Zealand from Marlborough to Wairarapa, including Wellington, confidence is moderate.

"While on Friday for Hawke's Bay south of Napier there is low confidence that west to northwest winds will become severe gale."

Additionally from late Thursday and during Friday, cold south to southwest winds following the front bring the likelihood of snow to low levels in the south of the country, says a MetService spokesperson.