Heavy rain deluges and thunderstorms are predicted for Auckland and Northland today and tomorrow – the first day of the new school term.

It is the the second weekend in a row tropically charged moist air has brought storm and flooding threats.

Between 6am and 6pm today there is the potential for localised downpours of 25 to 40mm per hour in Northland, which could occur with or without thunderstorms, MetService reported.

MetService meteorologist Surprise Mhlongo said the system will hit Northland first and hardest.

Northland’s heavy rain and severe thunderstorm watch, which was originally set until 3 pm, has now been extended to 6 pm today.

Mhlongo said Aucklanders can expect wet weather and potential thunderstorms today and tomorrow.

Thunderstorms are also possible for Coromandel Peninsula, Bay of Plenty and Gisborne.

“The weather system is very slow-moving so it’ll hang around between Auckland and Northland today with a definite possibility of thunderstorms tomorrow,” he said.

Civil Defence Northland has updated its online alerts, advising residents to take care while driving and look out for threatening weather.

“Rainfall of this intensity can cause surface and/or flash flooding, especially in low-lying areas … and may also lead to slips,” it warned.

The Transport Agency (NZTA) is also warning motorists to take care in the wet weather – to drive to the conditions, keep headlights on and maintain safe travel distances.

NZTA also advised Managamuka Gorge is closed due to a slip.

“There is a lot of uncertainty with respect to the amounts and distribution of significant heavy rain in Northland,” MetService warned, noting possibilities of flash flooding, surface flooding and challenging driving visibility in heavy rain.

The latest MetService thunderstorm risk suggests a moderate threat of thunderstorms in the Far North, north of Kaitāia to Bay of Islands, as well as heavy rain with intensities of 10-25mm per hour.

There is a moderate risk of thunderstorms spreading south over Northland, reaching Dargaville to Whangārei around midnight. There is also a low risk of thunderstorms over Auckland and the northern Coromandel Peninsula.

MetService meteorologist Sarah Haddon said warm, moist air is being pulled across the country by a low-pressure system in the north Tasman Sea.

The Metservice said there’s still a lot of uncertainty around the amounts and distribution of significant heavy rain in Northland.

“Downpours are possible. Amounts of rain are expected to approach warning criteria and possibly exceed them in localised areas, especially during thunderstorms and downpours,” the Metservice said.

The top of the North Island was battered as Cyclone Tam slowly rolled over the country last week.

More than 20 Far North homes are still without power a week after the ex-tropical cyclone struck the region.