Slim risk of more tornadoes tonight

The tornado ripped through Albany. Photo / Tim Wang

Metservice has confirmed there is a slim risk of more tornadoes this evening as a storm system passes over the upper North Island.

However, it says any more tornadoes will be smaller than the one that devastated buildings and killed one person in Albany this afternoon.

"The Severe Thunderstorm Outlook has been updated to remove the risk of any further damaging tornadoes over Auckland, Waikato, Coromandel Peninsula and Bay of Plenty, although a slim risk of smaller, less active tornadoes does still exist in some of these areas."

MetService Chief Forecaster Peter Kreft says New Zealand tornadoes are almost impossible to track as they are small, localised events and often occur without accompanying thunder and lightning.

Metservice weather ambassador Bob McDavitt says the tornado was a rare event caused by an unusual storm system over Auckland.

Weather maps show it formed around Silverdale before heading south to Albany, he said.

"Your heart has to go out to the ones who are affected in Albany. It's certainly horrific. There is horrific damange."

More investment in modern equipment is needed to enable New Zealand forecasters to predict tornadoes, Mr McDavitt says.

The system that caused today's tornado it is expected to dissipate around nightfall, he said.

Weather Watch chief analyst Philip Duncan said that based on initial evidence, the speed of the winds in the tornado would have been between 160kmh and 200 kmh.

In the tornado category system, which runs from EF0 to EF5, today's event was most likely an EF2, according to Mr Duncan.

While this is at the lower end of the scale compared to the type of tornadoes that have been ripping through the United States in recent weeks, it is still the largest tornado to hit New Zealand in several years.

"If the winds were strong enough to lift cars, they would probably be more than 200kmh and we just don't get events like this in New Zealand very often. Usually they are EF0 or 'mini-tornadoes'.

"This is just a taste compared to the recent events in the US, but this was the real thing for New Zealand and must have been frightening for those caught up in it."

Mr Duncan said the risk of another strike in Albany was not very high after this afternoon's event, with the wild weather moving away towards Great Barrier Island, but could not rule out further tornadoes in areas like the Bay of Plenty or Waikato.

Tornadoes are notoriously difficult to forecast, although weatherwatch.co.nz did specifically mention the Albany area earlier today in a weather warning that predicted heavy showers and thunderstorms in that area.

Mr Duncan said this type of event usually happened at this time of year.

"Most tornadoes take place in Autumn and Spring, and we thought there was the possibility of flash flooding with the weather today, but this has gone one step ahead with the rotation of the air.

"They are very hard to predict and the weather in today's situations can go from heavy downpour to light showers in a matter of minutes. But today did have perfect conditions for a tornado with the storms and all this unstable air swirling about."