Aucklanders are being warned to take shelter before a potentially damaging line of thunderstorms barrels over the city.

MetService issued an urgent thunderstorm alert for Auckland north of the Harbour Bridge with the risk of heavy rain and hail which could cause flash flooding and damage.

Severe thunderstorms have been detected on weather radars tracking east, and MetService expected the storms to lie near Auckland, Inner Hauraki Gulf, and Whangaparaoa at 3.15pm.

It comes after the newest Tropical Cyclone in the Pacific was named.

The Fijian MetService named Tropical Cyclone Judy today, which was sitting north of Vanuatu as of this afternoon.

New Zealand’s MetService expected Tropical Cyclone Judy would pass to the north of the country and wouldn’t have a “major impact” on our weather.

Niwa said this morning the latest modelling shows the storm missing New Zealand.

Niwa meteorologist Ben Noll told the Herald that ensemble forecasting involves running multiple instances of a forecast model, or “members” repeatedly to see if a pattern emerges.

By assessing the different scenarios, meteorologists can understand whether the different members agree or disagree with one another - and as weather systems draw closer, a consensus will too.

“There are inherent uncertainties in forecasting and over time those can compound.

“Niwa runs an ensemble system with 18 different members, you can understand if they’re vastly different or similar - for example, if we have 18 members in agreement, then the forecaster confidence is high but if they disagree we can understand how they diverge and communicate those different possible forecast scenarios.”

He said given the storm is still almost a week out, it will be monitored closely and while most members point to it missing New Zealand, there is a chance that could change.

“There may still be an ensemble monitor or two that tracks it a little closer.”

Thunderstorms, heavy rain threaten North Island

It comes after MetService issued a heavy rain watch for Gisborne from 9am this morning until 6am tomorrow, with up to 100mm of rain possible just north of Gisborne City.

Meanwhile, Bay of Plenty east of Kawerau and Coromandel were under heavy rain watches until later today and a severe thunderstorm watch covered the North Island from Northland to Manawatū.

Auckland, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua, Taupō, Hawke’s Bay, Taihape, Wanganui, Manawatū and Northland were under the severe thunderstorm watch until 9pm today.

The possible thunderstorms could bring torrential rain, hail and flash floods, MetService said.

Authorities are asking Aucklanders to stay vigilant, with more thunderstorms and heavy rain forecast for today.

In Auckland, the city’s emergency management group said advice from MetService warned of a moderate risk of localised downpours in the city of up to 40mm of rain per hour - and “possibly more”.

“These thunderstorms are expected to be slow-moving, bringing localised heavy rain and hail for some,” AEM duty controller Fleur Aldridge said.

“We are reminding Aucklanders to continue being vigilant as rainfall of this intensity can potentially lead to surface or flash flooding in low-lying areas.

”We also urge everyone to be cautious when driving as conditions could be hazardous with potential surface flooding and poor visibility.”

Driving conditions could become hazardous and people are urged to keep up to date with weather information.

Auckland Emergency Management reminded people to ensure their gutters and drains are clear of debris to lower the risk of flooding.