Western areas and the south were likely to get the brunt of the low which will cross the country on Friday through to Sunday.
"It will bring a mix of gales, rain, sun and showers," Mr Duncan said.
"Conditions on Saturday will be a bit stormy for some, but sunny, calmer, spells will also be in the mix - it is spring after all."
Wind-wise, strong to gale-force westerlies will build across the entire country on Saturday and the afternoons and evenings could see them at their height.
"It's still too early to lock in the best time to go out and vote but despite the wind and the rain we still see plenty of opportunities for people right over New Zealand to get out and vote this Saturday," Mr Duncan said.
For the Magpies, who take on Bay of Plenty in their second Ranfurly Shield challenge at McLean Park, the conditions could end up being familiar, with last Sunday's victorious outing against Otago played in strong winds and passing showers.
The other big Saturday event is Hawke's Bay Racing's JB Organics Spring Festival meeting at the Hastings Racecourse, featuring the Windsor Park Plate.
But conditions are unlikely to be severe enough to favour the mudlarks.
Saturday's forecast for the twin cities is a mix of sunshine at times as well as periods of rain, gusty northwesterlies with temperatures hovering a round 16C.
Sunday is similar, with showers hanging around off-and-on through until next Wednesday when sunshine and light winds return.