Atmospheric river bears down on NZ, gales, rain for north, fresh deluge for storm-hit south

MetService forecaster Samkelo Magwala told the Herald a low was developing in the Tasman Sea and would move towards New Zealand late Wednesday and early Thursday.

“It will result in heavy rainfall in the upper South Island as well as the central and upper North Island,” he said.

“The rain band will be accompanied by some thunderstorms and severe gales.”

Strong wind and heavy rain watches are forecast to begin on Thursday for Auckland, Great Barrier Island and the Coromandel Peninsula from 9am until 3pm.

Magwala said wind gusts could reach from 90-120km/h.

Emergency officials around Auckland are on alert before a stormy end for a second consecutive week, fearing flooding in parts.

Earth Sciences New Zealand meteorologist Chris Brandolino said an atmospheric river that stretched up to sub-tropical New Caledonia would sweep over much of the North Island and top of the South Island in coming days.

He said “beefy” thunderstorms were possibly set to hit Auckland during rush hour on Thursday, which would impact the evening commute. There was also a threat of damaging winds to sweep over the region.

At the same time, it would be warm and muggy with temperatures in the high teens.

Brandolino said people may want to do outdoor activities with their children during the school holidays, but “I would avoid that for much of the country, upper South Island, much of the North Island”.

“I would avoid Thursday certainly, I would avoid Friday and I might even avoid Saturday.”

The Waikato Regional Council has already moved to increase the water level of the Waikato River before the incoming storm.

“This measure is being undertaken to create additional capacity within the Waikato hydroelectric system in preparation for anticipated heavy rainfall later this week,” the council said in a Facebook post.

“This may result in temporary flooding at Grantham St and parts of the walkaways at or near Ann St in Hamilton.”

Further down the North Island, a 24-hour heavy rain warning has been issued for the Bay of Plenty from noon on Thursday with up to 180mm of rain forecast for the ranges.

For the top of the South Island, MetService has issued a heavy rain warning for the Tasman District west of Motueka from 3am to 9pm on Thursday.

A heavy rain warning is also forecast for the rest of the Tasman District, Nelson District and western parts of Marlborough.

Magwelo said the regions could be at risk of further flooding.

“Small amounts of general accumulation could result in floods.”

South Island officials prepare for more flooding

Nelson Tasman Civil Defence group controller Alec Louverdis told the Herald the region was still in the response phase after last week’s floods.

“We’re still trying to get infrastructure and lifelines updated and we’re still trying to deal with all the people who have been severely impacted,” he said.

Louverdis said the emergency management team was treating the upcoming heavy rain warning as the highest risk.

“If the event was on its own, it would be a different scenario. But on the back of what we have just experienced, we are taking absolutely no chances.”

Marlborough Emergency Management group manager and duty controller Matt Kerr said it was important for residents to remain vigilant and prepared after the recent weather event.

“We still have a state of local emergency declared in Marlborough, land is saturated and, in some areas, unstable so we may still see slips causing consequences for our communities,” he said.

Kerr said a large slip on Northbank Rd, north of Blenheim, was evidence the region’s roads and communities are still vulnerable.

In a post on its Facebook page, the Tasman District Council said: “This is not the news we wanted right now, given we are still in recovery from last week’s wet weather event, but here we are.”

The council said the forecasted combined totals and a short-duration event would produce low to moderate floods.

“However, we are far from normal, with very saturated ground and compromised infrastructures.”