Election-day forecast: Thunderstorm risk and heavy rain forecast across North Island

Voters heading to cast their ballots today may need to dodge more thunderstorms after lightning strikes sparked three fires across Auckland on Friday.

Three Auckland homes were damaged by fires sparked by lightning strikes as thunderstorms swept across the region on Friday afternoon.

A Severe Thunderstorm Watch is in force, with MetService warning there is a moderate risk of thunderstorms across the northern half of the North Island through Saturday morning.

The watch also covers some central parts of the South Island.

The thunderstorms could bring heavy rain of 10mm to 25mm an hour, with a moderate risk of severe thunderstorms capable of producing localised downpours of 25mm to 40mm an hour or more. MetService warned rainfall of that intensity could cause localised surface flooding and hazardous driving conditions.

The unsettled weather is being driven by a low-pressure system in the Tasman Sea drawing warm, moisture-laden subtropical air over New Zealand.

MetService meteorologist Clare O’Connor told the Herald that conditions were similar to yesterday, although it was impossible to predict exactly where thunderstorms would develop.

“There’s the right mix of warm air and unstable conditions, the right sort of ingredients for thunderstorms,” she said.

O’Connor said it was impossible to predict exactly where any storms would develop.

“There could be thunderstorms around today, but maybe it won’t be the same place as they were today. Maybe passing to the north or south of Auckland rather than right over Auckland like it did yesterday.”

She likened the thunderstorms to making popcorn kernels in a pot.

“Everything is there. You’ve got the heat, you’ve got the energy and everything. But it’s just which one is going to actually go pop first. We don’t know.”

The risk of thunderstorms is forecast to extend south across much of the North Island later on Saturday, while showery and unstable conditions are expected across large parts of the country.

Voters heading to polling booths have been advised to keep an eye on forecasts and rain radar updates, with showers expected to be intermittent rather than continuous throughout the day.

“Don’t let the weather put you off,” O’Connor said.

“It will be showers more than just continuous rain all day. So there’ll be breaks in the rain.”

Asked where the best place in the country would be for an election-day barbecue, O’Connor said there were few dry options.

“It’s not going to be the driest, unfortunately,” she said, noting much of the country was likely to see rain.

But if she had to choose...

“Actually, maybe Invercargill.”