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Hobsonville Storm Damage Track
Posted: Fri 11/01/2013 07:29
by NZstorm
For the record I'll post the damage track of the Hobsonville storm as surveyed by me.
Looked like an F1 magnitude event with winds of upto 90knots (170km/hr) I'm guessing.
Damage path is 500m+ wide with a length of around 5km.
Its unsual to get such strong thunderstorm dynamics over northern NZ in the summer months. Looking back at previous storm records the March 25 2005 severe thunderstorm/tornado event looks similar.
3 theories emerged for the cause of this damage, wet microburst, bow echo and tornado.
Re: Hobsonville Storm Damage Track
Posted: Fri 11/01/2013 07:43
by Manukau heads obs
The fact the destruction path gets wider
And curves narrows down the cause I would say
Re: Hobsonville Storm Damage Track
Posted: Fri 11/01/2013 10:11
by Richard
Was the wind not blowing in circulation motion which would have indicated a wet micro burst?
Re: Hobsonville Storm Damage Track
Posted: Fri 11/01/2013 11:51
by Weather Watcher
Nice work NZstorm. I agree with your estimates of the wind speed. I think it's high end EF1, or 170-180km/hr. From damage photos, it looks like the wind may have been strongest over the Whenuapai area (particulaly just north and northeast of the runway), and a little lighter over Hobsonville.
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 12:52
by NZstorm
Do you have the metars/speci 12pm to 1pm for NZWP available Weather Watcher?
I forgot to save them on the day and there is no online archive.
Looks like there was a strong surface boundary associated with the storm with the winds locally backing SW going by private weather station obs.
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 13:21
by Tornado Tim
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 14:03
by Orion
Manukau heads obs wrote:The fact the destruction path gets wider
And curves narrows down the cause I would say
I'm inclined to be 'meteorologically challenged' at times - can you explain further?
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 14:30
by Manukau heads obs
I don't a microburst would do that
(especially the curve)
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 15:28
by Nev
NZstorm wrote:Do you have the metars/speci 12pm to 1pm for NZWP available Weather Watcher?
The stats below ℅ NIWA might be of some help. Note that winds and gusts (in km/h) are the maxima during the previous hour (unlike metars which are taken on or just before the hour).
Code: Select all
Whenuapai Aero - Dec 6, 2012
NZDT T-max T-min hPa Wind Dir Gust Dir
11:00 23.5 21.8 1004.7 15.1 3° N 29.7 2° N
12:00 23.4 20.9 1003.2 18.1 57° ENE 31.5 69° ENE
13:00 20.8 18.7 1003.1 29.2 161° SSE 127.9 203° SSW
14:00 19.5 18.3 1003.1 14.8 220° SW 42.6 237° WSW
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 17:29
by Weather Watcher
The highest gust at Whenuapai AWS was 68.8kt recorded at 23:21 UTC.
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 18:52
by spwill
A lot of the damage at Hobsonville was done from wind out of the NW, I did see a spot where the trees/branches were snapped and lying in a N/NW direction.
I revisited Hobsonville a little while back. Two people at a store in Hobsonville told me they saw debris being thrown into the air as the storm approached. A radio eyewitness report (ZB) from the day mentions it raining pine needles/blossom just before the storm hit, then seeing air rushing sideways up the street , changing direction and trees coming up the street sideways.
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 19:44
by NZstorm
Thanks for the obs Nev and Weather watcher.
Its interesting the peak storm gust 68kts at NZWP was from the south (203deg). The damage at the top of the airfield was from NW wind (about 310deg).
When you consider the deep layer troposperic flow was from the NW a surface gust from the S of 68kts is remarkable.
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 20:17
by 03Stormchaser
Good to see ya work NZ
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 21:11
by Manukau heads obs
All pointjs to a tornado if you ask me
Heavy rain though can create wind of its own
Like a waterfall does...when the up draught dies I.r when
The cell collapses...I.e a microburst
But to me it does not fit that
But i could be wrong
Re: Hobsonville Storm Damage Track
Posted: Sun 13/01/2013 21:46
by METMAN
Pretty certain it was a microburst.
1. Tree damage in tornado has debri fallen forward on one side of track and debri fallen backward on the other due to circular motion of wind,(like a revolving propellor laid flat). This didn't happen tree debri fell forward both sides of track.
2. Pressure increased at Whenuapai at the time of the microburst. Identified as the 'pressure nose' signature of a microburst. With a tornado the pressure would have decreased.
Cause was CB feeding off ascending moist air (cooled at moist adiabatic lapse rate so warmer than outside air) running into an area of dry air (cooled at dry adiabatic lapse rate so not warmer than outside air) so the CB collapsed.
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 06:02
by Lacertae
Stop me if I'm wrong but a 500m+ wide damage path over 5km would involve a decent-sized tornado in terms of twister's diameter ?
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 07:22
by 03Stormchaser
METMAN wrote:Pretty certain it was a microburst.
1. Tree damage in tornado has debri fallen forward on one side of track and debri fallen backward on the other due to circular motion of wind,(like a revolving propellor laid flat). This didn't happen tree debri fell forward both sides of track.
2. Pressure increased at Whenuapai at the time of the microburst. Identified as the 'pressure nose' signature of a microburst. With a tornado the pressure would have decreased.
Cause was CB feeding off ascending moist air (cooled at moist adiabatic lapse rate so warmer than outside air) running into an area of dry air (cooled at dry adiabatic lapse rate so not warmer than outside air) so the CB collapsed.
Have you got some data/image etc to show the increase in pressure?
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 07:52
by NZstorm
There was a QLCS running across West Auckland and you would have a pressure rise along that.
The question is what was the pressure and temperature doing within the damage zone and do the NZWP obs represent this?
Where exactly is the AWS at NZWP?
Thanks for the input. Good to see the theories.
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 08:07
by Manukau heads obs
The pressure dipped at Ricky,s in grey lynn,as
The remains past over ,with a short period of torrential rain
And stronger wind
When i first saw that data,that's what made me think
Of a tornado
If it a microburst,then it must
be the strongest and largest
to
Have occurred in NZ
In either case,very severe
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 08:26
by spwill
There is a spot near the Bowls Club at Hobsonville where tree damage is lying back in a north direction but this looks to be an isolated occurrence of this.
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 08:40
by METMAN
03Stormchaser wrote:METMAN wrote:Pretty certain it was a microburst.
1. Tree damage in tornado has debri fallen forward on one side of track and debri fallen backward on the other due to circular motion of wind,(like a revolving propellor laid flat). This didn't happen tree debri fell forward both sides of track.
2. Pressure increased at Whenuapai at the time of the microburst. Identified as the 'pressure nose' signature of a microburst. With a tornado the pressure would have decreased.
Cause was CB feeding off ascending moist air (cooled at moist adiabatic lapse rate so warmer than outside air) running into an area of dry air (cooled at dry adiabatic lapse rate so not warmer than outside air) so the CB collapsed.
Have you got some data/image etc to show the increase in pressure?
Yes MetService has 1 minute data from WP AWS
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 08:46
by METMAN
NZstorm wrote:There was a QLCS running across West Auckland and you would have a pressure rise along that.
The question is what was the pressure and temperature doing within the damage zone and do the NZWP obs represent this?
Where exactly is the AWS at NZWP?
Thanks for the input. Good to see the theories.
There are two. One at either end of runway (NE and SW ends). Suspect data came from SW end as in NE flow aircraft would approach from that direction. Will confirm.
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 09:01
by Cook
Good work, NZstorm. Here are some images from
http://www.meted.ucar.edu/mesoprim/seve ... atures.htm and a radar image from the MetService blog with some scribbles on top.
Comet6.JPG
comet1.JPG
Comet2.JPG
Comet4.JPG
Radar1.JPG
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 09:04
by METMAN
Manukau heads obs wrote:The pressure dipped at Ricky,s in grey lynn,as
The remains past over ,with a short period of torrential rain
And stronger wind
When i first saw that data,that's what made me think
Of a tornado
If it a microburst,then it must
be the strongest and largest
to
Have occurred in NZ
In either case,very severe
Maybe first reported. If you were in a tornado or microburst you would notice little difference. (Microbursts can reach wind speeds 140 mph ). For some unknown reason they seem atracted to airport aproaches. (perhaps the dry air around the concrete runways?) Credible eyewitness reported it as being microburst with some funnel cloud activity associated with roll cloud ahead of the microburst.
Re: Hobsonville Storm Damage Track
Posted: Mon 14/01/2013 09:54
by Manukau heads obs
Great to see the detailed data
Looks like the microburst could have spawned some short lived whirwinds (that caused damage
Like a tornado)
Which is what I suggested initialy in the first thread (but called those whirlwinds (which had condensation
Cloud),a tornado)