A ridge of high pressure covering much of New Zealand on Tuesday is expected to move away to the east during Wednesday as a large trough approaches the country from the Tasman Sea.

"There is a degree of uncertainty about the position of lows within this trough," says a MetService spokesperson, "but it is possible that one low will pass near to the North Island on Wednesday or Thursday, bringing strong northeasterly winds and heavy rain to some places."

The MetService advises that there is low confidence that wind and/or rain warnings will be needed for Northland, Auckland, Coromandel Peninsula and parts of Waikato on Wednesday and Thursday.

Low confidence means a 20 per cent, or one in five chance, that the event will actually happen.

There is also low confidence that a heavy rain warning will be needed for Bay of Plenty on Thursday and Friday.

MetService expect that the trough should move onto New Zealand during Thursday or Friday.

Over the South Island, strong north to northeast winds are likely to bring heavy rain to the north and west of the Island.

There is moderate confidence that during Thursday and Friday warning amounts of rain will fall about western Tasman, northern Buller and much of Westland and low confidence that a rainfall warning will be needed about the remainder of Tasman, Buller and Westland as well as northern and central Fiordland.