Moist NW flow and severe weather, Upper NI, 5 Dec -

[spwill]

This tornado had a damage path over 100m, must be one of the wider tornadoes recorded in NZ..
A comment here by John key with regard to looking again at yesterdays weather forecasting to see if anything was missed.
http://www.nzherald.co.nz/nz/news/artic ... d=10852513

[Storm Struck]

Everyone is entitled to their own opinions on was it a tornado or not.. but I'm sorry, straight line winds, do not do this.

http://twitter.com/TroyRF/status/276759 ... 14/photo/1

Your right with the strength in the wind if that was caused by the tornado, or could it be caused by a lightning strike? CG's can blow the tops off trees or slit them in two.
I remember back in 2002 there was a beaut storm that ripped through on a southerly here and a tree in Rangiora was struck by lightning and split at the top it looked like that tree.

[Cook]

I have not read this entire thread but I did find the radar images posted here very interesting. If you would like to know why, please have a look at

http://en.wikipedia.org/wiki/Bow_echo

"Rear inflow jet

The formation of a bow echo requires a strong elevated rear inflow jet at mid-levels. The strength of the cold pool and mesohigh at the surface as well as warmer temperatures aloft due to convection works to create a mesolow at mid-levels which strengthens the jet. Upon reaching the edge of the convection the jet descends and spreads along the surface, generating straight-line winds.[4]"

If you want to use google to study this I recommend using the key words bow echo and rear inflow jet. Have a look, and then look at the radar images again. You see it, right?

I would VERY much like to know if anyone got a photo or video of the so called "tornado". If not, then I think the chances that this was a rear inflow jet are very high.

[NZstorm]

I would VERY much like to know if anyone got a photo or video of the so called "tornado". If not, then I think the chances that this was a rear inflow jet are very high.

Thanks for the interesting theory Cook. The storm was not photogenic due to low cloud and fog.

There is this clip of a tornado near Hobsonville yesterday, I'm not sure whether it has anything to do with the 12.15pm storm that did the damage.

http://www.nzherald.co.nz/national/news ... _id=129676

[Cook]

Thank you, NZstorm. That looks like a weak and very short lived twister, possibly on the edge of a downburst.

[spwill]

I would VERY much like to know if anyone got a photo or video of the so called "tornado". If not, then I think the chances that this was a rear inflow jet are very high.

Looking at the damage yesterday I favour tornado as the damage path was well defined, severe damage to no damage in a matter of metres. There was a confirmed tornado ( above clip ) at Greenhithe up stream from Hobsonville, I think the same tornado. Tornadoes are very much part of the climate around here, eg Ramarama, Albany and Avondale tornadoes are examples of quite recent tornado events and occured in similar situations

[Dale]

Everyone is entitled to their own opinions on was it a tornado or not.. but I'm sorry, straight line winds, do not do this.

http://twitter.com/TroyRF/status/276759 ... 14/photo/1

Your right with the strength in the wind if that was caused by the tornado, or could it be caused by a lightning strike? CG's can blow the tops off trees or slit them in two.
I remember back in 2002 there was a beaut storm that ripped through on a southerly here and a tree in Rangiora was struck by lightning and split at the top it looked like that tree.

Possible, but not probable mate. Next time you're over the hill here, when you head north into Greymouth from the Kumara Junction roundabout, look to your left.. there are acres and acres of massive pines which look just like that, some stripped bare, others laid over, lots with the trunks twisted completely off like the photo I linked up.. have reliable reports from work colleagues of a tornado which blasted through there a few years back but never got any mention as it didn't cause any structural damage persay.

[Tornado Tim]

Blog Post from Peter Kreft regarding the event:
http://blog.metservice.com/2012/12/hobs ... mber-2012/

No dopplar velocity images attached.

[Manukau heads obs]

WOW
reading that article just shows to me that more notice needs to be taken of ground reports!
I.e M/S are trying to say that the rain radar did not show it was severe enough to issue a watch?
it was reported here about how much lightning could be seen (and my boltec was picking up 10 to 15 strikes a minute, so there was lots of activity) as it approached and how black it was...something you are not going to know from Wellington
just look at the mama photo I put up early on...this was a CB that needed a watch on it from 10:15am



I find this statement amazing:

Interestingly, there are relatively few lightning strikes, and hence limited thunderstorm activity, in the greater Auckland area. This indicates that the thunderstorms were relatively small and short-lived

We had thunderand lightning here non stop (it would peak then weaken a bit, but never actualy stopped as such) for 2 hours!


Did M/S read the reports here of torrential rain at times?
(reported well before 1pm)
and some places got 60mm in 30 minutes...thats approaching record rain rates for NZ!

[Cook]

According to the MS blog: " “flares up” and then “collapses” within about a 10-minute period. The tornado is likely to have occurred during the few minutes in which this thunderstorm collapsed."

Along with what to me looks a notch in the bow echo where the severe weather was experienced and the fact that the storm "collapsed" points strongly to a rear inflow jet. The collapse is what brings the strong winds (energy) aloft to the ground.

I would also like to point out how difficult it is to analyze this, even with the benefit of hindsight.

Finally, at the end of the day it was strong wind that caused the damage. There does not seem to be conclusive evidence that shows this was due to a tornado and until such evidence is produced I find it regrettable that the media keeps going on and on about "the tornado". Guess what people will blame next time wind damage occurs? A tornado, regardless of whether one was observed or not or whether one occurred or not.

[spwill]

20C dewpoints for Auckland on Thursday morning, heating of the land , a thundery shower line moving in, surely there was always going to be the chance for severe weather. The first MetService severe thunderstorm was watch isued at 12.59pm, I think too late.

[Manukau heads obs]

it does look like it was a strong bow echo at the time on the rain radar
eye witness and video and damage paths all say its a tornado
but there also has been straight line winds
so both occured...thats my call

[NZstorm]

Peter kreft wrote

Could this tornado have been forecast?

No. Technology to forecast this type of tornado does not yet exist,

A week out in the models this set up was synoptically evident for severe thunderstorms and a tornado over northern NZ. The modelling was showing a very moist unstable boundary layer, considerable forced ascent, 0-6km shear values 60kts, 0-1km shear values 30kts+. All showed the potential for a range of severe convective mode including tornado.

[spwill]

it does look like it was a strong bow echo at the time on the rain radar
eye witness and video and damage paths all say its a tornado
but there also has been straight line winds
so both occured...thats my call

Yes

[GraemeWi]

I've driven past the damage path on SH18 (where it crossed over) 5 times in the last 2 days, if it was straight line winds the debris would have a very different distribution to what you can see. The tree damage where the large trees are shredded apart appears to be very different from knock down type events like you see after gales. I'm no expert but it doesn't look like straight line wind damage to me.

[jamie]

Metservice need to get off their high horse on this and admit defeat to a certain degree. Clearly tornadic damage as well as straight line. Social media and us etc were well ahead of them. A warning 45 mins after the deed is not on. It was severe before the big winds. If they followed the social media they could have had a warning out 5 mins after the deed. But in my opion that too would have been too late.

Yes it was hard to predict to a certain degree but there was enough there for them to be on it and issue better warnings. I have hardly any skills in severe weather and even I was getting excited by the models all week. I posted in here a number of times stating the mid week looks juicy. Why were they do far off the ball?

[Tornado Tim]

When trees topple over in the same direction it is most likely straight line winds, If in different directions then its more likely to be tornado damage.

I think some damage was due to straight line winds, however the images posted and eye witness evidence clearly shows a tornado occurred.
It is odd that that the tornado dropped in storms dissipating stage..... well according to Peter Kreft.

[spwill]

Peter kreft wrote,

As the storms approached Auckland, radar indicated that neither localised rainfall nor hail size would be sufficient to justify the issue of a Severe Thunderstorm Watch.

A Severe Thunderstorm Watch would cover possible future developments, severe thunderstorms did develop later.

[Tornado Tim]

Also adding from what you said Spwill,

As the storms approached Auckland, radar indicated that neither localised rainfall nor hail size would be sufficient to justify the issue of a Severe Thunderstorm Watch.

Strong wind from these storms could be detected on Dopplar Velocity, notice how the he didn't have it included in that post.
The omission of a dopplar velocity image in the blog post makes me suspicious that they are hiding something.
If they are, they can do so, as no one can view Doppler velocity images (not even on Metconnect according to a Meteorologist I had a conversation with).

[NZ Thunderstorm Soc]

Well seing this is an event that death occured, MetService have to be very cautious what they say other wize they could end up being in jail like those Italian earthquake geologists

[Manukau heads obs]

As the storms approached Auckland, radar indicated that neither localised rainfall nor hail size would be sufficient to justify the issue of a Severe Thunderstorm Watch.

The problem with relying solely on the rain radar is that the rain radar is after the fact
as a CB is developing, the strong updrafts hold the rain up in the thunderstorm

i.e it was in a rapid development phase as it approached the auckland area


the blitzortung lightning detection web site did a great job of showing it was very lightning active as it approached the western coastline, and it showed it was heading straight for the Waitekeres..I could see all that by 11:30am...thats when the watch at least should have gone out....all the signs were in place by then that it was going to be a doozey

also re the straight line winds:
I reckon youve got an embedded tornado ...and so the opposite tornado wind direction was bacily cancelled by the straight line wind, hence no damage from the opposite direction...i.e the tornado was the similar strength the straight line winds (i.e say 120 kmh), and so that doubled the wind speed...i.e 220kmh .....but the other side would have cancelled out, i.e no damage...thats why the footage of all the rubbish being blown up the street you suddenly get a doubling of the windspeed as the tornado goes up the street

thats my theory


M/S is welcome to phone me up for ground observations next time a setup like this
09 2355598

[Cook]

Yes it was hard to predict to a certain degree but there was enough there for them to be on it and issue better warnings. I have hardly any skills in severe weather and even I was getting excited by the models all week. I posted in here a number of times stating the mid week looks juicy. Why were they do far off the ball?

I wonder what good it would do the reputation of the MS if they started issuing watches and warnings every time it "looks juicy". That would make life easy for them but people would constantly be warned about severe weather that does not eventuate, to the degree that people would cease to pay much attention to warnings.

[RWood]

Yes it was hard to predict to a certain degree but there was enough there for them to be on it and issue better warnings. I have hardly any skills in severe weather and even I was getting excited by the models all week. I posted in here a number of times stating the mid week looks juicy. Why were they do far off the ball?

I wonder what good it would do the reputation of the MS if they started issuing watches and warnings every time it "looks juicy". That would make life easy for them but people would constantly be warned about severe weather that does not eventuate, to the degree that people would cease to pay much attention to warnings.

Yes. There's a UK forum where several posters complain constantly about MS issuing far too mnay warnings - one of these characters is an old curmudgeon who accuses them of being far too PC!! This issue is simply not as simple as the armchair critics would have one believe.

[Tornado Tim]

There's a UK forum where several posters complain constantly about MS issuing far too mnay warnings.

What?!, I find that real strange, how can they complain about a service that doesn't apply to there country.
Unless there is NZ users on that forum....
Were you meaning the UK Metoffice?

[RWood]

There's a UK forum where several posters complain constantly about MS issuing far too mnay warnings.

What?!, I find that real strange, how can they complain about a service that doesn't apply to there country.
Unless there is NZ users on that forum....
Were you meaning the UK Metoffice?

I meant their MetService - NZ is not on their radar at all ( no pun intended)

Beyond the warnings issue, I note how much proprietors of holiday accommodation in NZ hate it if there's any advance forecast of poor weather that doens't pan out perfectly - they'd rather the punters turned up and paid their money, even if the weather turns out to be really lousy.