'Tornado alley' terror
Northwest Auckland has been hit by three deadly tornados in 20 years but it would have been impossible to predict the tornado that claimed the lives of three men on Thursday, an expert says.
MetService meteorologist Daniel Corbett said the mixture of temperatures coming from the land and the sea, combined with wind speed, made it an ideal area for tornados to form.
Corbett said meteorologists could not predict tornados in the area. A radar used by staff was unable to spot the smaller kind of twister likely to strike in New Zealand.
"Our tornados are only tens of metres wide," he said.
"In the United States they are half-a-mile wide and the radar can pick up the whole thunderstorm turning.
"Because of the localised nature of these events they are undetectable and we have to forecast the conditions that would be favourable for tornados."
Twisters in the US occur in the warm season but tornados here were largely a colder weather phenomenon, he said.
"They're small, short-lived and dissipate within minutes."
Corbett said the Hobsonville tornado wasn't solely responsible for the destruction that caused about $13 million worth of damage - the straight line winds that went with it also played a part.
"At Whenuapai wind gusts of 110kmh were recorded and that alone can be very damaging."
He said the incident was a reminder to people to pay close attention to weather warnings about strong winds and heavy rain.
"Those are the days you want to plan to be at home or work and not be going out to the park.
"If you're in a tornado at home get into a closet or cupboard or go to the middle of your house keeping well away from glass. Otherwise get into your car if you've got nothing else."