A low pressure system to the north of the country is forecast to move slowly to the northeast of the North Island on Monday, says MetService.

On Tuesday, August 6, a south to southwest flow is expected to cover central and northern New Zealand, while a west to northwest flow will strengthen over the south of the South Island.

A front over the south Tasman Sea will approach the South Island on Wednesday, bringing increasing rain and strengthening northwest winds.

"There is low confidence for warning amount of rain in Fiordland and the southern half of Westland, and low confidence for severe northwest gales in Southland and Clutha, including Stewart Island," says a MetService spokesperson.

On Thursday, the front is forecast to move north over New Zealand.

"A strong northwest flow ahead of the front brings rain with some heavy falls to western areas of the country.

"At this stage there is low confidence for warning amounts of rain in Westland and Fiordland, and low confidence for severe northwest gales in Southland and Clutha, including Stewart Island.

"A cold and unsettled southerly flow spreads onto New Zealand following the front."