Wild weather predicted for the weekend could discourage voters on election day, taking a toll on the centre-left vote, an expert says.

The MetService has warned of gale-force winds and driving rain for the North Island and snow for the South Island on Saturday.

If the forecast is correct, it would be the first election-day snow since 1984.

AUT social sciences lecturer Dr Kate Nicholls said the conventional wisdom, internationally and locally, was that bad weather dampened voter turnout.

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And lower rates of voter participation would damage support for centre-left parties in particular.

"This could be especially damaging for Labour, given that voter turnout was at an all-time low in the 2011 election, continuing a long-term trend and Labour's base of support is already substantially eroded," Dr Nicholls said.

But centre-left parties, especially Labour, could also benefit from the early voting options available this year, Dr Nicholls said.

"Those likely to take the opportunity to vote early could include shift-workers, people reliant on public transport, and middle to low-income older voters, all of which fit Labour's demographic profile."

The Electoral Commission said yesterday 434,197 advance votes had been cast - far more than the 334,558 cast in 2011.

Victoria University political science Professor Jack Vowles said bad weather would deter some people from voting.

But the number would be small in proportion to overall voter turnout.

MetService meteorologist Elke Louw said Aucklanders should prepare for some severe wind gusts and rain, with a maximum temperature of 15C that would feel more like 11C or 12C.

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There was a chance the wind could reach warning or watch level, but forecasters would not know until closer to the time.

"We would recommend not to pack away the winter jumpers just yet."

Saturday's weather
Auckland: Morning rain, then showers. Strong gusty westerlies. High 15.
Whangarei: Morning rain then showers. Strong gusty westerlies. H 16.
Hamilton: Morning rain then showers. Strong gusty northwesterlies. H 14.
Tauranga: Rain developing, then showers. Strengthening westerlies. H 15.
Taupo: Morning rain, then showers. Strong gusty northwesterlies. H 11.
Napier: Brief rain at times. Strong gusty northwesterlies. H 16.
Wellington: Rain at times. Gusty northerly. H 13

- Source: Metservice