Avondale, Auckland Tornado - Sep 11

[NZstorm]

The roof damage in the photo below is on the south face of the house. The tropospheric wind flows were from the north. Good evidence of a tornado.

[NZstorm]

Also NZ's climatology favours tornadoes rather than destructive wind gusts. The reason for this is a tornado does not need much instability to occur where as destructive convective winds generally need good CAPE numbers.

[spwill]

There was twisting of vegetation, mud/debris splatter and damage path perhaps only 10m wide.

[Nev]

Bit belated but, I spoke to one of the witnesses at The Concourse, near the Lincoln Rd / NW Motorway interchange, and her description leaves little doubt in my mind that the tornado first touched down there, albeit very briefly.

She was inside the Aqua Technics Pool & Spa Centre there at the time with a few others, so didn't have the best view of the funnel itself. She said just after 1pm there was some rain, but didn't notice any thunder. Everything then suddenly went very dark, followed by a deafening roar. The roof started pulsing and they felt sure it was about to lift off. Heavy signs on the roof were torn off and everything outside started flying around in a circular motion. They watched a heavy industrial Waste Management bin on wheels going round and round in the car-park (it later took 3-4 strong guys to put it back in place). Large Palm trees were shredded of their fronds and a heavy ornamental fountain cemented to ground was ripped out. It lasted less than a few minutes, then the sun came back out and everything returned to normal, apart from debris scattered tens of metres in every direction. No neighbouring structures seemed to have suffered any damage, so very localised.

It would seem that the tornado must've retracted before briefly touching down again 2.3 km to the SE in Te Atatu South, causing some roof damage to 3 houses there. It then appears to have more or less followed the Whau River for another 3.8 km, before touching down again in Avondale, 'bunny-hopping' and hitting every third or fourth house in a straight line for another 1.0 km. So that's a total distance of about 7 km in a remarkably straight line from the 3 reported damage areas...

I've included another close-up of MetService's 1pm radar that day (c/o WZ), which clearly shows the preceding thunderstorm directly over the Avondale damage area ('+' marks the spot)...
.

[Manukau heads obs]

good work Nev

[spwill]

Thanks Nev, you have the Avondale path about right .

[NZstorm]

Excellent report there Nev.

The tornado occurred within the warm advection area of the low crossing the country and the moisture axis was very narrow. Dps were 14C around the time of the tornado.

[Manukau heads obs]

yes, so that clear slot on the rain radar is the gap between the warm and cold fronts?