Weather: 'Complex low' set to strike New Zealand next week, heavy rain warning issued

New Zealand's brief respite from bad weather is set to end next week as another low arrives, bringing heavy rain and possible severe gales.

Sunday is warm and humid as the low from Saturday departs. But on Monday a "complex low" hits the south.

"A complex low pressure system moves eastwards across New Zealand during Tuesday and Wednesday, bringing periods of heavy rain to the west of the South Island," MetService says.

A fresh warning has been issued for the area of Westland south of Otira starting 2pm on Monday, with locals warned to expect 90 to 140mm of rain.

"There is high confidence of rainfall reaching warning amounts in the ranges of Westland south of Otira, as detailed in the latest heavy rain warning," MetService says.

"There is low confidence of warning amounts of rain from Otira northwards to the ranges of Buller on Tuesday.

"In addition, as this system moves across the North Island on Wednesday, there is low confidence of westerly gales becoming severe over Auckland, Coromandel Peninsula and Northland."

Unsettled northwesterlies are expected across New Zealand during Thursday and Friday.

"There is low confidence of rainfall reaching warning accumulations over Fiordland during Thursday and Friday, and the Westland ranges on Friday," MetService says.