'Pinwheeling' low brings thunderstorms

A low "pinwheeling around New Zealand" will cause thunderstorms in Auckland this evening and a severe thunderstorm watch had been issued, MetService says.

MetService spokesman Daniel Corbett said the thunderstorms were triggered early this afternoon by a sea breeze convergence.

"You get the sea breeze bubbling up. You get the wind coming off the cooler sea warming in the land and you just get these two fronts of cloud meeting together."

The thunderstorms were "running up along the spine of the isthmus" from northwest of Silverdale in Auckland to northwest of Albany "all the way down to the Waitakeres and they're drifting slowly west-southwest", Mr Corbett said.

"There's a few more popping up across the city, they've got some thunder in them too."

A severe thunderstorm watch was currently in place for southern Northland, Auckland, down to Waikato and would be in place until 8pm tonight, Mr Corbett said.

MetService forecaster Hordur Thordarson said thunderstorms were expected to develop in Auckland, Waikato and Waitomo this afternoon.

"There is a risk that some of these could be slow moving and accompanied by downpours, 20 to 35mm/hr and hail.

"Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.

"Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain."

WeatherWatch spokesman Philip Duncan said afternoon cloud build ups were producing heavy showers around the Auckland, South Waikato and Central Plateau regions today.

The heavy showers could produce heavy downpours and risk localised flash and surface flooding, he said.

Isolated thunderstorms were also possible, Mr Duncan said.

"At the moment the main area of attention in the Auckland region is mostly north west of the CBD towards Helensville and down towards the Waitakere Ranges.

"Pockets of big showers will continue to pop up this afternoon around northern NZ before easing this evening."

Tomorrow more heavy showers and thunderstorms are expected across northern NZ including Auckland region, he said.

Meanwhile Hokitika and Milford were "basking in 23 - 24 degrees and sunshine", Mr Corbett said.