Thunderstorms, mini tornadoes, downpours: North Island to get lashed by wild weather

Heavy rain is set to swamp the North Island today, with the Bay of Plenty likely to bear the brunt of the downfalls.

Up to 120mm is expected to fall along the eastern coast from about 9pm tonight, while Mt Taranaki, Northland and Auckland all have heavy rain warnings in place from MetService.

Duty meteorologist Andrew James said the rain is the result of a low-pressure system swinging down from the north, which will bring warm temperatures but copious amounts of rain.

While some areas would already be experiencing a few showers, the full brunt of it won't be felt until tonight.

Given the rainfall, James said it was a timely reminder for homeowners to empty the gutters of their homes of any leaves which may have built up in recent weeks.

🌧Rain spreading south today 🌧

A front over Northland is expected to sink southwards today spreading rain over much of the North Island. Heavy Rain Warnings and Watches are in force for northern areas.

Stay up to date with your local forecast at https://t.co/Yjbq0jxdqz
^AR pic.twitter.com/SIdllZsbTs

— MetService (@MetService) April 19, 2021

"A low pressure system rolls in from the north over the course of today and tomorrow and brings heavy rain and strong wind to many parts of the North Island of Aotearoa.

"At the moment, Bay of Plenty and Rotorua are under a heavy rain warning and the remainder of the northern part of New Zealand, so that's from Auckland and Coromandel north are under a watch with Mt Taranaki under a watch as well."

The front will build up steam as it moves across the country, meaning the wider Bay of Plenty region is expected to get between 80mm and 120mm of rain.

"The low is sitting out to the west of the North Island at the moment and as that moves down there's a frontal system associated with that low that crosses the North Island."

The whole North Island will see some level of rain while just the tip of the South Island would be affected by heavy rain, James said.

"That system affects the top of the South Island a bit but not really much south of Blenheim and Nelson.

"It then rolls off to the east by Thursday morning. The main action will be gone by Wednesday evening."

In Auckland, the rain would get going this evening with the possibility of thunderstorms as well.

Heavy Rain Watch issued for AUCK, CORO, GTBAR, NTHLD, TNAKI https://t.co/gp4gw4XWmf

— MetService Severe Weather Info (@MetServiceWARN) April 19, 2021

"This warm air from the north does tend to bring what we call unstable conditions, which lead to the possibility of thunderstorms, so all through that upper North Island is the area where we would expect those."

There was also an "outside possibility" of mini tornadoes but as for where and when was anybody's guess, James said.

"Where and when they pop up is not really something that's able to be forecast.

"The main thing that people will notice is heavy rain and strong winds, and the possibility of localised thunderstorms."

By tomorrow morning it will likely be all over for Auckland and Northland, but Bay of Plenty will feel the affects a bit longer.

"There will be a shower or two in the back end of the day tomorrow for them."

Temperatures in both islands would continue to be mild, Whakatāne would have an overnight low tonight of 17C, while Timaru is set to reach 11C, both higher than average for this time of year.

The South Island would continue to enjoy cool but clear conditions with some areas set to get a few showers tomorrow.

Any showers in Christchurch should clear by tomorrow afternoon and temperatures there should remain stable during the day for the rest of the week but could drop a few degrees overnight from 11C to 6C by Sunday.