Warning of more tornadoes:NZ

There is a warning there could be more tornadoes like the one passing over Auckland.

Further thunderstorms are likely around eastern parts of Auckland down to northern Waikato, Coromandel and western Bay of Plenty over the next four hours, MetService warned at 4:30pm.

Some of the thunderstorms could be severe and there is a continued risk of one or two damaging tornadoes, it said.

People should take shelter immediately should more severe weather approach.

ONE News meteorologist Jim Hickey said a number of triggers are needed for a tornado to form.

“You need thunderstorms,” Hickey said. “The trigger points were warm, moist air coming in off the Pacific. We’ve had two days of that.

“Secondly, a cold pool coming around the western side of this low-pressure system. That’s clashed with that, causing this tremendous contrast.

“When you get cold air mixing with warm, moist air, instability and huge cauliflower top clouds form. So that’s what we’ve got.”

Hickey said a mixture of updrafts and downdrafts cause tornadoes to form rapidly.

However, he said the situation has improved with thunderstorms moving offshore, making it unlikely more tornadoes will form.

“They are dissipating and the energy forces are weakening. So it’s very unlikely more tornadoes are going to happen in the next 12 hours.”

Tornadoes were very rare in New Zealand because the land mass in much colder than tornado-prone areas like the southern US, Hickey said.

During May 1991, a tornado hit the small township of Albany, north of Auckland causing roofing iron to be lifted from homes and the destruction of a small church that was located on the south-western side of the village.

Copyright © 2011, Television New Zealand Limited

http://tvnz.co.nz/national-news/warning-more-tornadoes-4152978

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