It’s frosty across Aotearoa today with temperatures dropping below zero in Auckland as the national power grid emergency notice has been extended due to the extreme storm in space.

A cold start to the day risks putting extra strain on the country’s power supply, with some transmission lines in the North Island and South Island closed on Saturday as a precaution.

Metservice meteorologist Clare O’Connor said the coldest temperature recorded was in east Rangitāiki along State Highway 5 between Taupō and Napier, reaching a low of -8.7C.

Both Auckland and the central North Island recorded the coldest night temperatures of the year so far, dropping below zero.

Auckland dropped down to -0.4C in Whenuapai, said O’Connor.

O’Connor said Rotorua dropped to a chilly -3.3C, which is its second-coldest May temperature since 1972.

MetService forecaster Aidan Pyselman told the Herald the cold weather would continue across the country for the next few days.

Yesterday Transpower issued a “grid emergency” notice and shut down some transmission lines from operation due to the onset of the geomagnetic storm as a precaution. The galactic weather event was upgraded from severe to extreme, G5, the highest category scientists use to measure the storms.

Transpower, which operates the national power grid, said in a statement that the storm was likely to affect the Earth over the weekend because of significant solar activity.

“As part of our contingency plan, we are removing some transmission lines from service across the South Island as a precaution. In order to do this, we have to issue a grid emergency notice, however, this initial action should not impact supply of electricity to consumers.”

The notice was initially due to last until noon Saturday then it was extended until 6pm, and now it’s been moved to 8pm Sunday.

Transpower said on Saturday it did not anticipate any impact on New Zealand’s electricity supply to consumers at this stage.

Transpower grid development executive general manager John Clarke said he had been told the amount of disturbance around the Earth in this weather event was similar to the last G5 storm over 20 years ago.

At that level of severity, he was confident the solar storm should not impact the country’s electricity supply.

“This is sort of a rare event, it’s worldwide, it’s not unique to New Zealand. All grid operators will be thinking about out how they’re configuring their power systems right now with the level of solar activity,” Clarke said.

“I think consumers can be confident that we’ve done enough research to know what we need to do at the moment.”

While electricity did “wonderful things”, Clarke said people should always be prepared for the unexpected and have a plan to cope if the power was to go off for a day or two.

New Zealand’s energy supply was also facing heavy demand as a cold snap hit nationwide on Thursday last week. Kiwis were asked to avoid using appliances that morning and blackouts were not required.

AP reported the solar storm could produce northern lights in the US and potentially disrupt communications over the weekend. An extreme geomagnetic storm in 2003 took out power in Sweden and damaged power transformers in South Africa, the agency said.

A US National Oceanic and Atmospheric Administration forecaster said these storms, ranked on a scale of one to five, posed a risk for high-voltage transmission lines for power grids, not the electrical lines ordinarily found in people’s homes.

The last extreme geomagnetic storm hit the Earth in 2003, taking out power in Sweden and damaging power transformers in South Africa.

This article was originally published on the NZ Herald here.