‘Atmospheric river’ of heavy rain travels to Northland

Emergency response teams are urging the top of the North Island to get ready for extreme weather, with a potential second “atmospheric river” hitting the upper-North Island next week.

Metservice has issued a orange heavy rain warning and thunderstorm watch for Northland, as the heavy rain or “atmospheric river” moves northwards.

Northland Civil Defence Controller Graeme MacDonald said Northland should take the warning seriously and be prepared. Slips, road closures, and surface flooding were all possible.

In a briefing Niwa forecaster Ben Noll said it was likely another atmospheric river would hit the upper North Island next week.

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Victoria University professor of physical geography James Renwick said an atmospheric river was what meteorologists called river-like torrential rain.

The atmospheric river that had fallen over Auckland had been caused by a slow moving storm in the north Tasman Sea.

In the meantime, meteorologist Georgina Griffiths told Aucklanders to “hang in there”, with a reprieve from the extreme weather likely for Monday.

“From about dawn tomorrow it’s a rest day, a reprieve day … Use Monday to clean up and get yourselves sorted out.

There had already been light rainfall in parts of Auckland, but if rain was to increase to 10mm or 15mm an hour there may be some brief, localised, ankle-deep type flooding.

Their main concern for the remainder of today is the Northland region, she said.

“We are under heavy rainwatch until 6am tomorrow morning.”

A reprieve was coming for Monday, but a system of gale and rain would be coming through from the north again, affecting Northland significantly and coming into Auckland later Tuesday or Wednesday, she said.

Northland is likely to be the next region to undergo extreme weather, with the heavy rain experienced by Auckland and the Coromandel moving north this afternoon.

Metservice meteorologist Corrigan said he expected the rain to ease off as it moved across Auckland this afternoon, before reinvigorating as it hits Northland.

Auckland would be on heavy rain watch until 6am on Monday, with an increase of thunderstorms. A downpour of 20 to 40mm was predicted north of Orewa.

The rain over Coromandel had not relented since it had started on Thursday. The deluge was expected to intensify for the area, with 50 to 60 mm predicted across the ranges and lesser amounts around the coast.

The heavy rain would feed into the area’s rivers and catchments. People could expect more surface flooding, slips, and hazardous driving conditions. The orange warning for the Coromandel would end at 6pm tonight.

Corrigan said it was still uncertain where the heaviest rainfall would fall along the band of rain. Metservice would keep people informed.

There was also going to be isolated thunderstorms across the rest of the North Island this afternoon, separate from the line of rain stretching across the upper-North Island.

The risk of downpours was heavier around the Tararua district, Wairarapa, and the Ruahine range, with a risk of 25 to 40 mm of rain for those areas.

In Auckland, on-and-off showers will continue into Sunday “amping up” through the day as they become steady, heavy downpours. A heavy rain watch is in place for Auckland from 6am Sunday to 6am Monday.

Slow-moving low pressure will remain just west of the upper North Island until Tuesday when it moves east, according to the forecast.

It will bring rain and heavy showers through Auckland on Sunday, heading into Monday and possibly Tuesday.

The MetService forecast warned that while the upcoming rain should not match the intensity of that which fell on Friday, impacts were still “expected to be severe and wide-reaching”.

MetService said the rain would likely cause more flooding through northern regions over coming days.

Corrigan said MetService’s severe weather warning team was assessing the situation and would keep the public up to date with what was on the horizon.

Auckland was hit by torrential rain, with 245mm recorded at Auckland Airport in the 24 hours from 9am Friday, surpassing the previous record of 161mm by about 50%.

Some weather stations reported more than 80mm of rain in an hour.

MetService’s highest classification for intense rain is “torrential” – defined as 40mm of rain or more in an hour.

“That was truly record-breaking rain,” Corrigan said. “The likes of which we very rarely see in New Zealand and it just happened to be right over Auckland.”

People in areas facing rain warnings were advised to keep on top of forecasts and up to date with emergency investigations.