Heavy rain expected in Auckland and Northland as severe thunderstorm warning issued for Waikato

A severe thunderstorm warning has been issued to the Waikato region as Auckland and Northland are expected to be lashed with heavy rain overnight.

MetService issued Waikato, Hauraki, Matamata Piako and Waipa a severe thunderstorm warning until 10.37pm on Sunday.

“These thunderstorms are expected to be accompanied by torrential rain,” MetService said. “Torrential rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous.”

A severe thunderstorm watch remains in place for Auckland.

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Earlier, Aucklanders were sent an emergency mobile alert (EMA) on possible localised downpours in Auckland overnight.

This is the first EMA since heavy rain battered Auckland on Friday, and caused significant flooding, claiming four lives.

Auckland Emergency Management issued the alert at 7.47pm on Sunday, to provide important safety messages ahead of the potential for extremely heavy rain to hit the Auckland region.

MetService has issued an orange heavy rain warning to Auckland and Northland due to an active line of thunderstorms currently sitting over the Hauraki Gulf.

Between now and 7am Monday, this line of thunderstorms could produce localised downpours of 50-90mm of rainfall.

The possibility of localised extreme downpours up to 150mm cannot be ruled out, with the larger totals likely north of the Auckland Harbour Bridge.

“Given recent rainfall, the ground is extremely saturated which changes how rainfall can affect the environment,” Auckland Emergency Management Controller Mace Ward said.

“The decision to issue this alert was made so people in the region can make the best decisions of how to remain safe, should this heavy rain eventuate.”

People in the area between Ōrewa/Waiwera and down to Papakura/Drury, from coast to coast including Aotea Great Barrier Island are advised to make sure they stay informed and watch the forecast.

Any further updates would be posted to the Auckland Emergency Management social media channels.

At 11pm, MetService lifted the severe thunderstorm warning for Tauranga and Whakatāne in the Bay of Plenty.

A heavy rain watch remains in place for Coromandel Peninsula until 3am Monday and Waikato north and west of Cambridge until 5am Monday.

Meanwhile, in the South Island, a heavy rain watch has been issued to The Richmond and Bryant Ranges, the Rai Valley area and the Marlborough Sounds until midday Monday and Tasman northwest of Motueka until 3pm Monday.

A severe thunderstorm warning issued for Wellington earlier has been lifted.

Meanwhile, emergency response teams are urging the top of the North Island to get ready for more extreme weather, with a second “atmospheric river” possible.

MetService earlierissued an orange heavy rain warning and thunderstorm watch for Northland, as the heavy rain or “atmospheric river” moves northwards.

Although rain has eased in some areas, MetService meteorologist Angus Hines said we are not out of the woods yet.

“Large rainfall figures are still expected, and this is in addition to the immense rain which has already fallen,” Hines said.

While this rain will spread across many areas, there are places of particular concern.

“Northland is going to get waves of impactful rain in the coming days, especially overnight tonight (Sunday), and again from Tuesday.

“An Orange Rain Warning is in place for that area for the first of these waves, and more weather warnings are likely to be issued in the coming days,” said Hines.

These further bouts of upcoming rain could put stress on already saturated soils, causing more flooding and road closures, he said.

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.

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.

“Use Monday to clean up and get yourselves sorted out.

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

The rain over Coromandel had not relented since starting on Thursday – feeding into the area’s rivers and catchments. .

The Bay of Plenty had also been hit hard over the last 36 hours, with one location seeing more than 302mm of rain.

In the Waitomo region, extensive flooding resulted in a state of emergency being declared on Saturday evening.

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

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 – the likes of which we very rarely see in New Zealand and it just happened to be right over Auckland,” Corrigan said.

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