Thunderstorm watch lifted after hail, rain and thousands of lightning strikes

A fresh bout of thunderstorms is rolling over Auckland city, with conditions so poor a major sporting fixture has been delayed. 

A red severe thunderstorm has been issued for much of the region this evenign as deafening cracks of thunder, torrential rain and hail sweep across Auckland late afternoon on election day.

The worst of the weather is expected to hit at 5.22pm stretching from Whangaparāoa to Hunua.

Earlier MetService issued a severe thunderstorm warning for Waikato, Waitākere, Franklin and Rodney at 2.24pm, warning of torrential rain, hail and possible flash flooding.

That warning has since been lifted.

At 2.07pm, a weather radar detected severe thunderstorms near Kumeū, Manukau Heads, Piha, Muriwai Beach, Waimauku and Huapai, as well as offshore from Auckland’s west coast.

The storms were moving south-southeast towards Āwhitu, Waiuku, Port Waikato and Glenbrook.

MetService warned the storms could produce localised downpours of 25mm to 40mm an hour, potentially causing surface flooding and hazardous driving conditions.

MetService meteorologist Devlin Lynden told the Herald the large hailstones were caused by a warm, moisture-laden weather system moving over the North Island.

“We have a pretty warm weather system pushing in over the North Island, and that’s warm with a lot of moisture as well,” he said.

The combination of heat and moisture had created ideal conditions for severe thunderstorms.

Lynden said hailstones formed when warm, moist air near the ground rose rapidly into the atmosphere, where temperatures were much colder.

“What happens is that warm air lifts up from the surface into the atmosphere and cools down really rapidly.

“And as it cools down, it freezes and then is able to fall out as these big hailstones that you’ve seen on social media.”

He said the dramatic weather was not entirely unexpected as New Zealand approached summer.

“Given the time of year, you know, we’re approaching summer, things are heating up, thunder, lightning, hail, they’re all sort of more summery weather patterns.

“It’s pretty interesting weather, but it’s not out of the blue.”

Aucklanders heading to cast their vote on Saturday may need to dodge thunderstorms. Photo / MetService

MetService meteorologist Clare O’Connor earlier told the Herald conditions were similar to Friday, 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.

“There could be thunderstorms around today, but maybe it won’t be the same place as they were yesterday. 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.”

O’Connor said the humid conditions were helping create the instability needed for thunderstorms to form.

The risk of thunderstorms was forecast to extend south across much of the North Island later on Saturday, while showery and unstable conditions were 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.”