A sudden storm has sprung a surprise on Auckland, with barrelling thunder, hundreds of lightning strikes and large hailstones thumping the region on Tuesday.
MetService has issued a severe thunderstorm warning for Northland, Auckland, Waikato and the Coromandel.
There were 870 lightning strikes recorded across the country between 11am and 4.45pm, with 370 of those in Auckland, a MetService spokeswoman said.
MetService was "expecting more to come" on Tuesday evening, she said.
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The large number of lightning strikes prompted Niwa to issue a warning to get off the water.
The storm manifested itself in hyper-local pockets, with some Aucklanders not experiencing any of the rain, hail or thunder that struck other parts of the city.
'MY DRAINPIPE FROZE SOLID'
Karaka resident Kelly Newby said her house was pelted by a 30-minute hailstorm before the sun came out again.
"Its brilliant and sunny now but it came out of nowhere. It just pelted down massive stones of ice.
"It looked like it had snowed – everything was blanketed in white.
"They were really big, not quite golf ball-sized but some near enough.
"It came in really thick, it was banging on the windscreen of the car windows and our downpipe from the guttering was frozen solid.
"Our vege garden has been totally blown to bits, and our flower gardens have been pelted to pieces," Newby said.
Hailstorms and heavy rain damaged four shops in Takanini village, forcing them to close early.
Large hailstones had blocked stormwater pipes, sending water gushing into a block of shops about 1pm.
A second onset of extreme weather caused the roof of NCQ Technology to give way.
Debris and computer parts were scattered along the footpath outside the store.
Owner Faris Hamama said it had happened "so quickly".
Hamama had just moved stock back in to the store from Big Boys Toys an hour earlier.
"It was just really bad luck."
Spark had closed its doors, and staff could be seen sweeping water inside.
Next door, House of Travel staff were dodging leaks throughout their office.
Store owner Craig Hopley said they had been watching the hail come down when a light fixture starting springing a leak.
"Seconds later it was like a waterfall," he said.
"I just told my staff: get out."
Just as quickly as it had started, the sky had cleared – but hailstones still blanketed the berm outside the strip of shops.
STORMS 'LIKE POPPING POPCORN'
NIWA meteorologist Ben Knoll likened the pockets of extreme weather to popping popcorn.
"Thunderstorms in the atmosphere are kind of like popcorn popping in a microwave. You don't know which kernel, or cloud, is going to pop first.
"It's that random. When the kernel pops it's kind of like the cloud ballooning up into the atmosphere and blossoming out into a thunderstorm.
"It's due to the uneven heating of the land that we live on, some areas are going to get heated more than others and that leads to the destabilisation of the atmosphere."
SEVERE THUNDERSTORM WARNING
MetService warned the storms are slow-moving and could bring downpours to some areas, with flooding reported in the south Auckland suburb of Takanini.
Reports came in from about 12pm that hail, thunder and lightning was starting to roll across the region.
Niwa urged people to get off Auckland's waters, warning "you're the tallest thing in the water".
Metservice meteorologist April Clark said there was a ridge over the country with an upper trough causing the sudden storm over Auckland.
"If you've got that upper trough above it, the winds accelerate upwards and form thunderstorms," Clark said.
"The issue here is they are very slow moving so where those wind convergences are setting up, they are not changing, so basically, the thunderstorm is setting up in a place and not going anywhere.
"This is creating high rainfall."
Clark said the last time she checked, the highest was 19 millimetres in one hour, which was "quite significant".
The storm would be easing off by late evening, but thunderstorms would still be forming until the wind died down, she said.
Although some places in Auckland had become sunny, Clark said east Auckland was seeing a lot of the storm.
"There is definitely the potential for it to flare up again as things heat up because they need that heating from the land to get more beefy thunderstorms.
"There is a chance until tonight that the same thing [thunderstorms] could happen," Clark said.
Clark added that it looked like there was a light southwesterly setting up over West Auckland creating a chance for the storm to come back, but it was more likely that thunderstorms would persist in east Auckland.
"We're not ruling it out but at the moment the west is probably a little more safe than the east," she said.
Lightning, hail and rain rolled across West Auckland before heading south across the city.
Children competing at a Te Atatū school cross country were caught in the hail storm, but the event was called off when the lightning started, a parent said.
"Crazy, noisy weather. Thunder, lightening, hail, rain in Henderson Valley and now brilliant sunshine," Sara Romans wrote on Facebook.
The lightning storm then headed to Pukekohe to the south of Clevedon, with 27 lightning strikes in the space of five minutes.
NIWA principal scientist Chris Brandolino said these sorts of weather events are fairly common at this time of year.
"Spring is really everything goes," he said.
However, Brandolino said that the rain was a brief respite from an expected period of prolonged dryness facing the country, particularly in the South Island and lower North Island.