Philip Duncan: What caused the South Auckland tornado?

One person is dead, one injured and residents of more than 1200 mostly Papatoetoe homes - 60 of which are now uninhabitable - have been left picking up the pieces after an ordinary Saturday morning turned to terror when a tornado ripped through South Auckland.
It was just before 8.30am when the tornado struck, in a matter of seconds tearing off roofs and garage doors, uprooting trees, smashing windows, toppling a truck and power poles - some on to cars - and leaving stunned residents cowering and praying in their homes from Manurewa to Papatoetoe.
They estimated more than 1200 homes had been affected by the tornado, with the majority without power.
An Auckland Emergency Management spokeswoman said a family of eight and a family of three were provided with accommodation last night.
She said Auckland Emergency Management were holding a debriefing and planning session this morning and would provide an update about 9.30am.
Fire and Emergency and Urban Search and Rescue teams had so far assessed 240 as being impacted by the tornado, 60 of which were uninhabitable.
Assessments would continue today, so the number of tornado-damaged homes could increase, Auckland Emergency Management controller Parul Sood said last night.
At a Ports of Auckland yard on Wiri Station Rd, dozens of stacked shipping containers collapsed as the powerful funnel of spinning air crossed Wiri, with at least one container weighing 30 tonnes tossed into the air.
A contractor not employed directly for the Auckland Council-owned port company was killed and a truck driver on site injured but it's understood the fallen shipping containers may not be directly responsible for the death.
The injured truck driver was taken to Middlemore Hospital with moderate injuries, a St John spokeswoman said.
Auckland mayor Phil Goff said he'd been told someone at the yard died after the force of the wind threw them some distance in the air and they then struck a solid object.
"I want to be careful about that [cause of death]. I've had conversations about it … I've talked to Ports of Auckland, they said the force of the wind was so strong that 30-tonne containers were being picked up and blown about in the air."
A person at the yard described the scene as "carnage", with distraught workers watching as three ambulances, a specialist response team and multiple police officers rushed to help, with someone being "worked on" in the back of an ambulance.
As well as toppled containers, including the 30-tonne one lifted by the wind, signs from the neighbouring motorway were also blown onto the site, Ports of Auckland spokesman Matt Ball said.
"We're very shocked by what is a horrendous freak event and our thoughts are with the family and friends of the people who've been affected.
"This will be difficult for our staff. They're not just affected by what's happened at work, many of them also live in the area."
Papatoetoe and Manurewa residents described terrifying scenes as the tornado cut a swathe of destruction across parts of both suburbs, sparking 100 calls to Fire and Emergency New Zealand.
More than 20 crews were sent to help.
Because the tornado, although destructive, was localised and brief it didn't cross paths with any wind gauges, so wind speeds weren't known, MetService forecaster Gerard Bellam said.
The rain gauge at Auckland Airport in Mangere recorded 25mm in the hour to 9am yesterday, with the downpours "a good indication of the amount of energy that was around", Bellam said.
Many residents were still asleep in bed or only just awake when the noise of the tornado alerted them to the approaching danger.
"The noise was horrendous … it sounded like a plane was landing on our house," said Annelise Greenfield, who huddled in the hallway with her husband and three kids, hugging and praying, as the tornado tore its way up Grande Vue Rd in Papatoetoe.
"My 10-year-old...

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