Hobsonville Storm Damage Track

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spwill
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Re: Hobsonville Storm Damage Track

Unread post by spwill »

There is the footage of a tornado at Greenhithe on the day ( NZ Herald). Clip shows this storm about 2km from Whenuapai, it appears to be moving in from the NW, east of Whenuapai/Hobsonville
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

That is really interesting. I was told about wind shrieking outside Albany Westgate at a bit after twelve. I wondered about the possibilty of another wind arc running up Lucas Creek to Albany. That footage seems to confirm that, if it was taken towards Lucas Creek.
After a microburst hits the ground the winds diverge through 360 degrees, but as these winds radiate out it breaks down into separate arcs of hurricane force winds. The tornado which they called a funnel cloud probably a Gustnado which can form briefly in the turbulent winds if they exceed 60 kts. The winds are heavy and will take the lowest route and travelling over water there is less drag and high wind speed can be maintained.
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Re: Hobsonville Storm Damage Track

Unread post by Manukau heads obs »

A gustnado does make sense
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Re: Hobsonville Storm Damage Track

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The bow echo theory is the theory that is emerging here. A bow echo looks like it accounts for directional wind changes such as the SSW 69kts at NZWP (meso vortex). It also accounts for the squall moving through Greenhithe. More research to do on it.


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Westgate is Massey not at Albany.
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Re: Hobsonville Storm Damage Track

Unread post by spwill »

It is a shame there is not more footage with the Greenhithe clip.

Does the convergent tree damage at Hobsonville and the big change in wind direction during the wind storm fit a microburst ?
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Re: Hobsonville Storm Damage Track

Unread post by Nev »

spwill wrote:I heard an interesting report from Hobsonville today of a work site office that was lifted off the ground and carried through the air in a general west direction for about 100m with a worker inside it, the office was dumped to the ground before being picked up again by a change of wind direction and carried through the air for some distance in a general east direction. This occurred near the corner of Clark and Scott Rd


There's a video interview with the guy that was inside that site-office/container, which rolled across Scott Rd, then rolled back again, which would mean winds roughly from the NE, then from the SW.

Copy of video here (ignore the opening pic, which is the May Albany tornado).
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Westgate is Massey not at Albany.
I think he means Albany Westfield? ;-)

There's also a pic here taken from the top floor of the North Shore Police Station (Glenfield?) of what appears to be a highly airborne sheet of corrugated iron and is said to have travelled several kms.
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Re: Hobsonville Storm Damage Track

Unread post by spwill »

There's a video interview with the guy that was inside that site-office/container, which rolled across Scott Rd, then rolled back again, which would mean winds roughly from the NE, then from the SW.
Thanks Nev, yes that is the location, I was repeating a story told to me.
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Re: Hobsonville Storm Damage Track

Unread post by spwill »

Tree damage shows the wind change
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

NZstorm wrote:The bow echo theory is the theory that is emerging here. A bow echo looks like it accounts for directional wind changes such as the SSW 69kts at NZWP (meso vortex). It also accounts for the squall moving through Greenhithe. More research to do on it.


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Westgate is Massey not at Albany.
oops Westfield not Westgate
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Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

Thanks for the links Nev.

The Police station is at Constellation Drive. The iron will have been lifted from the Glenfield area rather than Hobsonville.

Another question about this event is how the Rotorua event ties in with this. Where they the same thing. Certainly appear to be.
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Re: Hobsonville Storm Damage Track

Unread post by RODALCO »

Attached is a photo of the readings on a weather station of one of my work collegues.
165.6 km / h was measured.
He lives about 2 kms from where the actual tornado struck.
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Who put the LED's on the lightning arrestor ?
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Re: Hobsonville Storm Damage Track

Unread post by RODALCO »

Photo taken off one of the damaged trees near Monteray Park car museum.
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Re: Hobsonville Storm Damage Track

Unread post by Manukau heads obs »

WOW,that is huge windspeed measurement!
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

what I think happened. Looking at Auckland Weather Radar 2307 you can see white dots in the centre of a red line These white dots are super saturated water droplets in a CB. Looking at Auckland Weather Radar 2315 you can see that most of the super saturated water droplets have gone. This tells a meteorologist that the CB is collapsing (microburst) also in 2315 you can see the shape of the red line has become more circular due to water droplets diverging outward at base as it collapses. The top of the collapsing column is 10km high and water droplets fall reaching terminal velocity about 40kts the air moving down at same speed (friction) hits the ground, horizontal speed doubles to 80kts (compression) the heavy air has to get away quick as more is falling the CB moving at 25kts to SE radiates an arc (80kt) up Lucas Creek to NE. The main arc radiates to SE moving 80kts plus speed of CB making strength 105 kts
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Nev wrote:
spwill wrote:I heard an interesting report from Hobsonville today of a work site office that was lifted off the ground and carried through the air in a general west direction for about 100m with a worker inside it, the office was dumped to the ground before being picked up again by a change of wind direction and carried through the air for some distance in a general east direction. This occurred near the corner of Clark and Scott Rd


There's a video interview with the guy that was inside that site-office/container, which rolled across Scott Rd, then rolled back again, which would mean winds roughly from the NE, then from the SW.

Copy of video here (ignore the opening pic, which is the May Albany tornado).
NZstorm wrote:Metman

That works for microburst if he goes to SE first then a lull then a slightly less strong wind to NW
Westgate is Massey not at Albany.
I think he means Albany Westfield? ;-)

There's also a pic here taken from the top floor of the North Shore Police Station (Glenfield?) of what appears to be a highly airborne sheet of corrugated iron and is said to have travelled several kms.
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

spwill wrote:It is a shame there is not more footage with the Greenhithe clip.

Does the convergent tree damage at Hobsonville and the big change in wind direction during the wind storm fit a microburst ?
Yep. a microburst certainly has big wind changes (shears) that is why aircraft crash.
Say you reverse a vacumn to blow point it downwards and then move it along.
The wind speeds would be about 80 kt (I think) except to the front which will be stronger due to additional speed of movement. I know that in actual microburst the diverging wind breaks into strong arcs but best example I can think of
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

spwill wrote:
There's a video interview with the guy that was inside that site-office/container, which rolled across Scott Rd, then rolled back again, which would mean winds roughly from the NE, then from the SW.
Thanks Nev, yes that is the location, I was repeating a story told to me.
That works for a microburst If the winds came from NW True and then SE True. Why many people mistake them for tornadoes. But they don't have the spinning top rotation except for possible funnel clouds or brief weak tornadoes. It is the non rotating (straight line winds) which do the damage
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Re: Hobsonville Storm Damage Track

Unread post by Tornado Tim »

METMAN wrote:water droplets fall reaching terminal velocity about 40kts the air moving down at same speed (friction) hits the ground, horizontal speed doubles to 80kts (compression) the heavy air has to get away quick as more is falling the CB moving at 25kts to SE radiates an arc (80kt) up Lucas Creek to NE. The main arc radiates to SE moving 80kts plus speed of CB making strength 105 kts
Where are you getting these figures from? As far as I am aware there is no way to get a volumetric weight of Water vapour in a cloud nor highly accurate way of getting how much area the water vapour is covering. (Radar data is far to coarse), in order to calculate the downward velocity in a microburst.
Could you provide/quote the calculations/data used which lead you to your figures quoted above?
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Re: Hobsonville Storm Damage Track

Unread post by Manukau heads obs »

See my earlier post about how a waterfall creates surprisingly strong winds
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Re: Hobsonville Storm Damage Track

Unread post by Tornado Tim »

Manukau heads obs wrote:See my earlier post about how a waterfall creates surprisingly strong winds
I understand how a microburst develops and acts but I would want specifics to back up his claim.
Without it, it carries no weight at all.
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Re: Hobsonville Storm Damage Track

Unread post by spwill »

METMAN wrote:.
Say you reverse a vacumn to blow point it downwards and then move it along.
Surely with a microburst air flow would weaken as it moves out from the storm and this would be reflected in the damage, particularly the tree damage to atleast some degree. Damage path is narrow along the track.
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Re: Hobsonville Storm Damage Track

Unread post by Manukau heads obs »

Thats the other thing
How long does a microburst normaly last?
7 minutes (between radar scans)
The forward speed of the cb was not 20kts ,re the idea that got the windspeed up to 105kts
I.e you would think it would not be self sustaining?
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Tornado Tim wrote:
METMAN wrote:water droplets fall reaching terminal velocity about 40kts the air moving down at same speed (friction) hits the ground, horizontal speed doubles to 80kts (compression) the heavy air has to get away quick as more is falling the CB moving at 25kts to SE radiates an arc (80kt) up Lucas Creek to NE. The main arc radiates to SE moving 80kts plus speed of CB making strength 105 kts
Where are you getting these figures from? As far as I am aware there is no way to get a volumetric weight of Water vapour in a cloud nor highly accurate way of getting how much area the water vapour is covering. (Radar data is far to coarse), in order to calculate the downward velocity in a microburst.
Could you provide/quote the calculations/data used which lead you to your figures quoted above?
The height of tropopause was 40,300ft that day. It was a severe CB so its height would have reached up to the trop, it can't go any higher. The terminal velocity of frozen raindrops/hail (44kts) was used as guide to calculating downdraft until in 83 President Reagen landed in Airforce One at Edwards Air Force Base 7 min later it was struck by 150mph microburst. They started the GEOS project, put a doppler radar on a stationary satellite and looked at microbursts. I saw two results of their measurements of microburst downdrafts. A normal sized one 40kts an extra large one 52kts. Thats why 80 kts is a common windspeed for microbursts.
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Manukau heads obs wrote:Thats the other thing
How long does a microburst normaly last?
Good question will try to find out
7 minutes (between radar scans)
Its a doppler radar
The forward speed of the cb was not 20kts ,re the idea that got the windspeed up to 105kts
From reports it was moving neither fast or slow (15kts slow 30kts fast I estimated 20/25kts I just tried to get actual speed from radar I made it roughly 19 mph) Try to imagine a waterblaser pointing straightdown moving at 20 mph but the water hitting something (ground) moves ahead of it much faster
I.e you would think it would not be self sustaining?
Its 40,000 ft high and collapsing far bigger event than Albany tornado

I really enjoy these questions makes me have to think
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Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Manukau heads obs wrote:Thats the other thing
How long does a microburst normaly last?
7 minutes (between radar scans)
The forward speed of the cb was not 20kts ,re the idea that got the windspeed up to 105kts
I.e you would think it would not be self sustaining?

In the states the norm is 5 min but they can last up tp 30 min
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