Sth Auckland Funnel/Spout - Apr 20

[Tornado Tim]

What do the Base Velocity scans show on the spout? (probably not much, but would be good to see all the same)

[Nev]

TVNZ and TV3's pics suggest that it may not have touched down...

'Stunning and rare cloud funnel captivates South Auckland' - TVNZ

'Funnel cloud sweeps over south Auckland' - TV3

[Manukau heads obs]

one of the best composition photos I have seen .....main street waiuku

TVNZ and TV3's pics suggest that it may not have touched down...

one of those photos looks to be from a dairy farm..but also at at early stage...when it was still growing...i.e it got bigger than that
That part of the main street is angled SSE..so that makes the funnel between SSE and SE of Waiuku Jamie...to help in pin pointing it

[jamie]

Great pics!

[NZstorm]

GFS showed a W converging with a N to produce that funnel. But what ever the wind directions at the time, there would have been a convergence boundary to generate the vorticity. I'm sure we get smaller scale versions quite regularly but they go unnoticed or unreported.

Great photo from Waiuku main street!

[spwill]

Certainly a photogenic spout

[Weather Watcher]

Here are the reflectivity and velocity images from the Auckland radar at 4:45pm yesterday. In the velocity image, green is towards the radar and yellow is away. Note that at this distance from the radar, the radar is scanning at about 2km above the ground. The velocity image does show a possible velocity couplet in the shower south of Waiuku, but this did not show in the previous or later scans. The dark green pixel (which is about -14.5m/s) is probably incorrect - I trust the yellow and lighter green ones more.

[Manukau heads obs]

Excellent
Thanks for posting the images Met Service

[Nev]

Bit belated but, I thought 30 odd posts probably warranted a separate thread.

And yeah, love the mainstreet Waiuku pic, and thanks for the radar-imagery MS…

[NZstorm]

It was a fairly well developed looking landspout so a couplet could possibly have shown up.

[RODALCO]

Amazing photo's, thanks for sharing.

[spwill]

A little bit of info here on landspout tornadoes with this report on a recent landspout in California
http://www.wrh.noaa.gov/psr/pns/2015/Ap ... Center.php

[NZstorm]

A fundamental difference between a landspout and mesocyclonic tornado is the role of the RFD (rear flank downdraft). The later needs descending air to occur which wraps around the updraft. Landspouts develop within rising air only.

[spwill]

With a mesocyclonic tornado the rotation starts in the cloud, with a landspout tornado the rotation of air starts below the cloud and may even start at ground level before it is pulled up the cloud.

With tornadoes a condensation funnel does not need to be visible all the way from cloud to ground.

[NZstorm]

With a mesocyclonic tornado the rotation starts in the cloud, with a landspout tornado the rotation of air starts below the cloud and may even start at ground level before it is pulled up the cloud.

With all tornadoes the rotation starts on or near the surface. The source of the rotation is different though. Landspouts develop from vertical vorticity that spins up along surface boundaries when the surface layer is heated. For supercell tornadoes low level directional shear creates horizontal vorticity which is then tilted upwards by the storm updraft and taken into the cloud. And the deeper layer shear maintains the mesocyclone.

[Manukau heads obs]

the other type of Tornado is one we get in NZ that can occur on active cold fronts
they wont be always associated with a mesocyclone
is that a 3rd type or are they always just a landspout?
(and then you get another type like on the west coast of the SI where its the low level shear setup by the coastal NEer running parallel to the mountrain range)

[NZstorm]

the other type of Tornado is one we get in NZ that can occur on active cold fronts
they wont be always associated with a mesocyclone
is that a 3rd type or are they always just a landspout?
(and then you get another type like on the west coast of the SI where its the low level shear setup by the coastal NEer running parallel to the mountrain range)

I would label them as mini supercells. These occur in high shear, low CAPE environments. The surface air needs to be humid, most NZ tornadoes occur with dewpoints the 14C to 17C range.

[Tornado Tim]

Orographic Induced Supercell seems more applicable to me (wouldnt apply in this case though). Southern Brasil gets quite a bit of Orographic induced Supercells,
The Xanxerê Tornado being the most recent.

[Manukau heads obs]

http://www.al.com/news/huntsville/index ... rm_on.html

[KiwiWeather]

Terrific photos Brian !!!
Great thread.