Showers on election morning are due to clear, leaving settled weather for much of the country as voters head to the polls.
MetService is forecasting showers in parts of the North Island, clearing in the afternoon, and fine weather elsewhere - apart from rain on the South Island's West Coast, and in Invercargill and Dunedin.
From Sunday, the tail end of a heat wave in New South Wales will start to be felt on the east coast of New Zealand.
Temperatures in parts of New South Wales are forecast to soar as high as 40°C and to reach 33°C in Sydney.
"New South Wales has never had a 40°C day in September and that may happen," NIWA meteorologist Chris Brandolino told Morning Report.
On Sunday and Monday, temperatures in New Zealand will be "pretty warm" especially across eastern parts of both islands.
On Sunday, daytime temperatures in eastern parts of the country will be 4-6°C above the September average and on Monday as high as 5-8°C above average, he said.
The election weekend coincides with the spring equinox and the start of daylight saving, when clocks go forward an hour early Sunday morning.