Heavy rain, small tornadoes possible for North Island

Storm clouds over the Auckland Harbour Bridge. Photo / Greg Bowker

There is a chance of small tornadoes today as heavy rain and high winds will again lash parts of the North Island still recovering from wild weather in recent weeks.

Severe weather warnings have been issued for the Bay of Plenty and northern Gisborne - north of Ruatoria, with 70-90mm of rainfall forecast in these areas from this morning through to midnight.

"There has been a succession of heavy rain events for these regions so they certainly don't need more," MetService forecaster Heath Gullery said.

Small tornadoes possible
"There is a chance of bands of heavy showers and thunderstorms passing across the northern half of the North Island through the course of today," Mr Gullery said. "With those there is the chance of localised heavy rain and strong wind gusts of up to 100km/h possible, and the chance of one or two small tornadoes."

Although any tornadoes which may form are likely to be smaller than the devastating one which ripped through Albany on Tuesday, Mr Gullery said it was hard to rule it out.

"It is notoriously difficult thing to forecast. There is an outside chance of one a similar size to the one on Tuesday but I think if they do occur they are more likely to be small."

Mr Gullery also said it was hard to forecast where and when tornadoes would likely form.

"Unfortunately given the very small scale of these things it is almost impossible to forecast when they are going to hit and the intensity they are going to be. We can only really forecast the potential where they might form but not exactly where they are going to be.

"For any of those regions from Taranaki across to Taupo and up to the Bay of Plenty and then northwards to Northland and Auckland there is the chance over the course of the day to getting those thunderstorms.

"Unfortunately given the very small scale of these things they are almost impossible to forecast when they are going to hit and the intensity they are going to be. We can only really forecast the potential where they might form but not exactly where they are going to be.

Civil Defence prepared
In any case, Civil Defence said it is ready to react immediately should more tornadoes hit Auckland today.

Auckland Civil Defence Controller Clive Manley said despite the warning tornadoes are possible, it is hard to predict where and if a tornado will hit.

"You don't really know where it would be if it would come, but what it does do though is put us on extra alert so people are ready to scale up if needed," he told Newstalk ZB.

He said there are duty officers monitoring these sorts of events all the time to ensure a rapid response.

Meanwhile Civil Defence has released some guidelines for what to do in a tornado. Mr Manley said if one does occur, people should stay inside and stay close to the ground.

"If they're caught outdoors and if there is a hollow or a trench or a ditch, they can go in there, cover their head while the tornado goes over the top is the best thing to do.".

Mr Manley said if driving, people should try get out of their cars.

More unsettled weather to come
Mr Gullery said the weather will remain unsettled over the weekend.
"There is going to be several fronts and relatively deep lows passing across New Zealand during Saturday and Sunday. I would advise people to keep up to date with the latest forecasts in their areas and be aware of the weather in the region."

Mr Gullery said MetService generally forecast for the next five to seven days and the weather will remain unsettled over that time.
"There is this unsettled autumn-time weather we often get. A lot of fronts and troughs come across the Tasman Sea and New Zealand this time of year.

"Hopefully in the next week or two we will see if there will be a prolonged spell but at this stage it is too early to say."