Much of the North Island is expected to be wet on Sunday.
"There will be showers in the west and north but it will be mainly fine elsewhere until late afternoon," MetService meteorologist Claire Flynn said.
In the South Island, wet weather and a cold snap is expected on Saturday, with the weather moving up the country.
MetService has put a severe weather watch in place for the western ranges of Westland and Fiordland as rainfall accumulations could reach short-term warning levels of 70mm in 12 hours on Saturday afternoon.
There is also a possibility of severe gale force winds in exposed areas of the South Island.
Flynn said the weather will be mainly dry for Marlborough, Canterbury and North Otago.
Buller, Nelson and Marlborough will get rain on Sunday morning before it moves away to the north.
After a wet end to the weekend tomorrow, the weather is expected to improve - temporarily - on Monday as a ridge of high pressure moves onto the North Island.
However, the worst is yet to come as another, slow-moving front makes its way up the country mid next week, preceded by northwesterly winds.
"It could be getting quite windy for the lower North Island and upper South," said Flynn.
Rain could be heavy for a time on Monday, particularly above the rangers and in the west and south of the South Island.
Weekend weather:
Whangarei
Saturday: High 27C, low 19C. Cloudy periods.
Sunday: High 30C, low 17C. Showers and northwesterly winds.
Auckland
Saturday: High 24C, low 17C. Fine, with some morning and evening cloud.
Sunday: High 25C, low 17C. Rain and northwesterly winds.
Thames
Saturday: High 26C, low 16C. Fine, with some morning and evening cloud.
Sunday: High 26C, low 15C. Rain and northwesterly winds.
Napier
Saturday: High 24C, low 19C. Mainly fine.
Sunday: High 31C, low 17C. Mainly fine apart from brief rain.
Wellington
Saturday: High 18C, low 15C. Cloudy periods and strong northerlies developing.
Sunday: High 21C, low 14C. Morning rain then mainly fine. Northerlies easing.
Christchurch
Saturday: High 26C, low 14C. Increasing cloud, a few spots of rain.
Sunday: High 27C, low 10C. Mainly fine.
Dunedin
Saturday: High 21C, low 13C. Cloudy with a few showers.
Sunday: High 23C, low 12C. Mainly fine. Northerlies turning to southerly for a time.