Any thunderstorms could produce localised heavy rain of 10 to 20mm/h along with small hail.
Tomorrow an active front would reach the lower South Island, bringing rain to the West Coast and Southern Alps, and strong or gale force northwest to eastern areas.
Heavy rain was forecast about Fiordland and parts of Westland on Saturday, continuing in Westland on Sunday, and through the Otago and Canterbury headwaters.
Southern Fiordland and Southland could see some severe gale northwesterly winds on Saturday, and inland parts of Otago and Canterbury from Saturday to Sunday.
The North Island was in for a mostly fine weekend until the front arrived late on Sunday.
Ahead of the front, temperatures across most of the country would bump up a couple of notches with warm northwesterly winds, with the North Island's east coast the place to be.
The front would move northeast across the North Island on Monday, bringing rain to western areas.
Tropical Cyclone Liua formed in the Southwest Pacific near the southern Soloman Islands last night.
The category one cyclone was the first to form during the month of September in the southwest Pacific since Tropical Cyclone 02P on September 12, 1950.
Malivuk said the cyclone was forecast to weaken over the weekend, and slowly move southwest into the Coral Sea.
Today's weather
Whangārei
Fine. Southwest breezes. 17C high, 6C overnight.
Auckland
Fine apart from isolated showers in the west. Southwest breezes. 16C high, 8C overnight.
Hamilton
Long fine spells. Possible shower. Light winds. 16C high, 3C overnight.
Tauranga
Fine. Southwest breeze. 17C high, 6C overnight.
New Plymouth Long fine spells. A morning shower or two. Southwest breezes. 15C high, 7C overnight.
Napier Fine morning. Becoming cloudy this afternoon and showers developing this evening. Light winds. 14C high, 3C overnight.
Whanganui Long fine spells. Westerly breezes. 16C high, 7C overnight.
Wellington Cloudy at times. Northerlies. 14C high, 9C overnight.
Nelson Long fine spells, chance afternoon shower. Light winds. 14C high, 5C overnight.
Christchurch Fine. Light winds. 15C high, 2C overnight.
Dunedin Fine. Northeasterlies developing this afternoon. 13C high, 6C overnight.