South Island Storms 20/11/19

[tgsnoopy]

My question is, what the hell was it?! Tornado? Or something else? Whatever it was it has cost us an awful lot of money in a very short space of time!

Sounded like it may have been some form of straight line winds. Tornadic damage tends to lay one way on one side and the opposite on the other side of the path, in between can be either due to the circulation. Southern Hemisphere tornadoes tend to rotate clockwise looking down, whereas Northern Hemisphere tend to rotate counterclockwise when looking down. Have a second look, if it was a downburst/microburst (more likely I'd think) the outer edges will possibly have angled away from the centre. Be very interesting to know. Suggest lots of photo's & contact Metservice/NIWA one of them may be interested in evaluating the damage & be in a position to give you answers. Thanks for sharing.

[grinch]

Thanks guys. So it sounds like this thing has travelled at least 10-15kms in a very narrow path. Would a downburst do that? Unfortunately its not easy to really study the pattern of the damage as it has travelled over a lot of open country and through single tree lines. It would be great to see some footage from the air, especially if it has gone through any plantations on its way.

[spwill]

Thanks guys. So it sounds like this thing has travelled at least 10-15kms in a very narrow path. Would a downburst do that? Unfortunately its not easy to really study the pattern of the damage as it has travelled over a lot of open country and through single tree lines. It would be great to see some footage from the air, especially if it has gone through any plantations on its way.

I think a downburst can start off very narrow but given the day it was possibly a tornado, a condensation funnel is not necessarily visible with a tornado.

[tgsnoopy]

Thanks guys. So it sounds like this thing has travelled at least 10-15kms in a very narrow path. Would a downburst do that? Unfortunately its not easy to really study the pattern of the damage as it has travelled over a lot of open country and through single tree lines. It would be great to see some footage from the air, especially if it has gone through any plantations on its way.

Ok, that sounds more likely be a tornado, but the damage path should give that away. Know anyone with a drone? I recall you giving the impression everything had fallen the same way, I'm not used to seeing that kind of damage when looking at the damage path (I've seen more than a few).

[grinch]

A few more photos if anyone is able to make any sense of them. (They just look like a row of fallen trees to me haha.) The treeline runs north-south and all the trees have fallen roughly to the north-east. Certainly nothing whatsoever has fallen over the other side. No I don't know anyone with a drone unfortunately.

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[tgsnoopy]

A few more photos if anyone is able to make any sense of them. (They just look like a row of fallen trees to me haha.) The treeline runs north-south and all the trees have fallen roughly to the north-east. Certainly nothing whatsoever has fallen over the other side.

The image quality is unfortunately not the best due to the small size. To me in the latest pics it doesn't look like uniform direction which would suggest a possible tornado. NWS in the US uses diagrams which show where the origin position was, and the centre of where it ended up. They draw a line between to show the direction they moved. If the direction of movement is uniform unlikely to be a tornado. if the edges lie one way on one side, the opposite way on the other and a mixture in between it implies a tornado.

[Nev]

Also bear in mind that tornadoes usually have faster winds on one side than the other, due to its forward momentum, i.e. the faster its forward speed, the greater the difference in wind speeds on each side of the tornado. So that may account for more damage on one side of its path than the other.

[NZstorm]

From the photos you can see where the weakest point of many trees are, in the root system. Its not unusual to see trees felled like this by high winds or tornadoes.

My thoughts are if the damage occurred in the storm (precipitation) it would have been a microburst for sure. If the damage occurred ahead of the precipitation where the temperature was still up a bit with an easterly then a tornado probable.

[grinch]

My thoughts are if the damage occurred in the storm (precipitation) it would have been a microburst for sure. If the damage occurred ahead of the precipitation where the temperature was still up a bit with an easterly then a tornado probable.

Unfortunately I don't really remember the details of how things exactly played out. I was too busy cacking myself!

[Razor]

Thanks guys. So it sounds like this thing has travelled at least 10-15kms in a very narrow path. Would a downburst do that? Unfortunately its not easy to really study the pattern of the damage as it has travelled over a lot of open country and through single tree lines. It would be great to see some footage from the air, especially if it has gone through any plantations on its way.

Gee if this had gone through Christchurch things would have been rather catastrophic! All the best out there Grinch

[tgsnoopy]

Also bear in mind that tornadoes usually have faster winds on one side than the other, due to its forward momentum, i.e. the faster its forward speed, the greater the difference in wind speeds on each side of the tornado. So that may account for more damage on one side of its path than the other.

Yes I recall that, one side having more damage than the other being common, but the key factor that opposing side of the damage path have opposing direction damage. If we weren't very very busy at work, I might have tried to get down for a look. I suggest (Is Metservice or NIWA paying attention?) this is an event worthy of investigation.

[Thunder081]

^ Thanks Thunder081. Note that your timestamps are in NZST rather than NZDT.

Okay thanks. All future timelapses will be in NZDT

[Razor]

I thought I'd bring this one back as its coming up to one of a couple of "anniversary dates" for 2 of last years biggest weather events - the other being the early December floods that literally cut the South Island into 2 islands at least in the transport sense

In interesting article in todays news, the Timaru Hailstorm is now officially most expensive weather insurance event in NZ this century, at $170 Million. That's $3,600 in payouts averaged for every man woman and child in the district as the attached article cites.

https://www.stuff.co.nz/timaru-herald/n ... -170m-mark

[NZ Thunderstorm Soc]

Yes. I read the above article in this morning's Timaru Herald.
Both of these events were local and affected a lot of people

[tornado]

i remember tracking this storm on radar up here in auckland. Was interesting indeed.