Hobsonville Storm Damage Track

Archive of NZ Weather & Climate
Forum rules
These topics are a read-only archive and may be subject to out-of-date information.

For today's weather discussion head to: New Zealand Weather & Climate
User avatar
NZstorm
Posts: 11333
Joined: Mon 10/03/2003 19:38
Location: Grey Lynn, Auckland
Has thanked: 342 times
Been thanked: 361 times

Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

Do we have an accurate fix on the time of the storm passing Hobsonville?

We need the next scan of the radar after 2315hr. Is Weather Watcher able to supply please?
Weather Watcher
MetService Meteorologist
Posts: 283
Joined: Sat 15/03/2003 10:59
Location: Upper Hutt, NZ
Has thanked: 3 times
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by Weather Watcher »

Here's the 23:22 UTC image...
You do not have the required permissions to view the files attached to this post.
User avatar
NZstorm
Posts: 11333
Joined: Mon 10/03/2003 19:38
Location: Grey Lynn, Auckland
Has thanked: 342 times
Been thanked: 361 times

Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

Thanks for the sat pic Weather Watcher.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Yep tks Weather Watcher. Sure has quietened down a lot. Get a lot better idea of speed.

I make it 30mph or 26kts
User avatar
NZstorm
Posts: 11333
Joined: Mon 10/03/2003 19:38
Location: Grey Lynn, Auckland
Has thanked: 342 times
Been thanked: 361 times

Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

METMAN wrote:Yep tks Weather Watcher. Sure has quietened down a lot. Get a lot better idea of speed.

I make it 30mph or 26kts
The upper steering flow was NW40kts. Some propagation effects from the low level NE flow is what would slow the movement down.

It would be interesting to see the 1 minute AWS from NZWP.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Has anybody else noticed some thing odd about the radar pictures. Everythings seems to far west.
In the 2307UTC (1207NZST) the strongest part of CB where microburst, tornado or bow arc has got to originate from is about over Huapai. Yet a witness on TV said it started (WP?) at 1210 NZST.
Even at 2315 UTC main part still looks west of HB. Suspect the overlay may be set a bit too far to east?
In the 2315UTC I would like to push the eastern edge of red sector to be covering the upper harbour.
What do you think
spwill
Posts: 9907
Joined: Sun 29/06/2003 22:39
Location: Mt Eden Auckland
Has thanked: 839 times
Been thanked: 866 times

Re: Hobsonville Storm Damage Track

Unread post by spwill »

The general damage pattern at Hobsoville has a convergent look to it which seems to go against the idea of air flow diverging from the center of the storm as with a microburst. Southwest wind and northeast wind showing up edit, and the NW as well. When you drive down Scott Road the damage there has a more straight line look to it, much of the tree damage lying in a southwest direction there.
Last edited by spwill on Mon 21/01/2013 10:11, edited 1 time in total.
User avatar
Tornado Tim
Moderator
Posts: 4920
Joined: Sun 19/10/2008 17:17
Location: Raglan, Waikato / Hillcrest, Hamilton
Has thanked: 102 times
Been thanked: 202 times
Contact:

Re: Hobsonville Storm Damage Track

Unread post by Tornado Tim »

METMAN wrote:Has anybody else noticed some thing odd about the radar pictures. Everythings seems to far west.
In the 2307UTC (1207NZST) the strongest part of CB where microburst, tornado or bow arc has got to originate from is about over Huapai. Yet a witness on TV said it started (WP?) at 1210 NZST.
Even at 2315 UTC main part still looks west of HB. Suspect the overlay may be set a bit too far to east?
In the 2315UTC I would like to push the eastern edge of red sector to be covering the upper harbour.
What do you think
Static radar image output isnt extremely accurate. As it's overlayed ontop of GIS layers, which is only as accurate as the surveys being conducted. You need to look at the raw echo return (which I am not sure if metservice has an archive to).
NZAPStrike.net - NZ Aus Pacific Strike Network
User avatar
Nev
Moderator
Posts: 6216
Joined: Tue 07/03/2006 15:24
Location: Waiheke Island, Hauraki Gulf
Has thanked: 468 times
Been thanked: 1064 times

Re: Hobsonville Storm Damage Track

Unread post by Nev »

Also, if it takes 7 minutes to complete a scan, wouldn't parts the resulting image be older than others?

I also suspect that the convenient time-stamps, in multiples of 7.5 minutes from the hour, could be up to a few minutes out compared to real-time obs.
Weather Watcher
MetService Meteorologist
Posts: 283
Joined: Sat 15/03/2003 10:59
Location: Upper Hutt, NZ
Has thanked: 3 times
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by Weather Watcher »

The radar images are 0.5 degree (beam elevation) PPI Reflectivity images, which take about 20 seconds to do a complete 360 degree scan (i.e. produce the image you see).

The complete radar volume is made up of 15 elevation angles from 0.5 to 20 degrees, and this take about 5 minutes to collect (i.e. 15 x 20 seconds).

The overlaid grid is correct.
User avatar
NZstorm
Posts: 11333
Joined: Mon 10/03/2003 19:38
Location: Grey Lynn, Auckland
Has thanked: 342 times
Been thanked: 361 times

Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

A typical microburst wind pattern as mapped in a sugarcane field in Florida. The FOS 70kts was an AWS.

Quite a spread in the wind pattern.
You do not have the required permissions to view the files attached to this post.
User avatar
Nev
Moderator
Posts: 6216
Joined: Tue 07/03/2006 15:24
Location: Waiheke Island, Hauraki Gulf
Has thanked: 468 times
Been thanked: 1064 times

Re: Hobsonville Storm Damage Track

Unread post by Nev »

Ah, thanks for the clarification Weather Watcher. That makes more sense. :-)

Would be interesting to see if the 1 minute WP AWS data did indeed show a significant pressure-spike?


Also found this little snippet interesting…
Downbursts - Severe Weather Awareness - NOAA

Trees were "twisted" off - so it must have been a tornado
This is one of the most common mistakes - the fact that trees were "twisted" off doesn't necessarily mean a tornado has gone through. If you could draw a line straight down a tree, you'd see that the tree isn't exactly alike from one side to the other. Differences in limbs and leaves may cause the tree to have more wind resistance on one side than the other. The tree begins to "twist" (much like a stop sign "twists" in strong winds), if wind speeds are high enough the tree will begin to tear apart in a twisting motion -even though the winds are relatively straight!

The best way to determine if damage was caused by a tornado or a downburst is to fly over the area and look down on the damage path.
User avatar
Tornado Tim
Moderator
Posts: 4920
Joined: Sun 19/10/2008 17:17
Location: Raglan, Waikato / Hillcrest, Hamilton
Has thanked: 102 times
Been thanked: 202 times
Contact:

Re: Hobsonville Storm Damage Track

Unread post by Tornado Tim »

I have a theory also if a CB has a lot of precip contained within it, there would be in theory be allot more air that has to be displaced when it falls.
Since more precip = more weight = more downward acceleration= stronger potential sfc straight line wind.

What was the max DBZ rating in the storm?
Weather Watcher? Could you post a copy of the Doppler velocity image for 23:22 UTC?

Even though radar beams are quite elevated from the SFC, there should be some indications from the outspread of the microburst.
NZAPStrike.net - NZ Aus Pacific Strike Network
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Ive assumed edge of blue in cb was over start of storm damage at 1210 then backed it up to NW 1.5 miles and made it 2.5km further West than radar. Shifting CB image 2.5km west in 1215 radar. This puts centre of CB over HB. Something interesting appears at Lucas Creek. We now have a ribbon of precipitation running NNE (NE would be better) from Lucas Creek to Albany. Could this be what was filmed at Greenhithe. Long bow I know.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

spwill wrote:The general damage pattern at Hobsoville has a convergent look to it which seems to go against the idea of air flow diverging from the center of the storm as with a microburst. Southwest wind and northeast wind showing up edit, and the NW as well. When you drive down Scott Road the damage there has a more straight line look to it, much of the tree damage lying in a southwest direction there.
You have me in my weak area how strong were the other divergent flows . There could have been other strong wind arc flows but I would guess they were about 40 to 60kts. Don't know. However the usual width of damage swathe for a NZ tornado is 18 metres (source NIWA). It would have to be a huge tornado (by NZ standards) to create a damage swathe 500 metres across.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

NZstorm wrote:A typical microburst wind pattern as mapped in a sugarcane field in Florida. The FOS 70kts was an AWS.

Quite a spread in the wind pattern.
Thats great I was looking for some info like that but couldn't find any.
I did see a photo with two damage swathes in tree plantation. One from a tornado and one from microburst.
Easy to tell apart as microburst had all the trees fallen over the tornado one had no trees they were all gone.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Hi Nev I asked RNZAF if they had taken any photos of damage but they said they didn't think they had.
Will ask again
jamie
Posts: 5907
Joined: Fri 25/02/2011 21:35
Location: Hamilton NZ
Has thanked: 22 times
Been thanked: 273 times
Contact:

Re: Hobsonville Storm Damage Track

Unread post by jamie »

Im really enjoying the conversion/research going on here guys. Keep up the good work.

Whats the total length of the damage? Do we have a definitive speed the storm was moving? Based on this couldnt you work out how long it took for the storm to "collapse"?

The frustrating thing is i had access to the 1min obs for Whenuapai at the time. I even looked at it and saw the spike in wind speed. I never worried about looking at wind direction. I was focused on finding the top wind speed. It expires after 60mins so i no longer have access.

Weather Watcher should be able to give these to us im sure? Also dopplar wind would be interesting to see. The size of the damage seems big enough to be able to pick up on radar. Although this only shows "to and from" winds and wind speed its better than nothing
spwill
Posts: 9907
Joined: Sun 29/06/2003 22:39
Location: Mt Eden Auckland
Has thanked: 839 times
Been thanked: 866 times

Re: Hobsonville Storm Damage Track

Unread post by spwill »

METMAN wrote,
However the usual width of damage swathe for a NZ tornado is 18 metres (source NIWA). It would have to be a huge tornado (by NZ standards) to create a damage swathe 500 metres across.
The event was unusual, how many microburst events have there been around Auckland over the years. Yes, if it was a tornado it would have been a very large tornado for this part of the world.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

This came from MetService
" All the barometric pressures in it's path jumped as the CB passed over"
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

jamie wrote:Im really enjoying the conversion/research going on here guys. Keep up the good work.

Whats the total length of the damage? Do we have a definitive speed the storm was moving? Based on this couldnt you work out how long it took for the storm to "collapse"?

The frustrating thing is i had access to the 1min obs for Whenuapai at the time. I even looked at it and saw the spike in wind speed. I never worried about looking at wind direction. I was focused on finding the top wind speed. It expires after 60mins so i no longer have access.

Weather Watcher should be able to give these to us im sure? Also dopplar wind would be interesting to see. The size of the damage seems big enough to be able to pick up on radar. Although this only shows "to and from" winds and wind speed its better than nothing
Where damage starts WP to where it ends HB about 5km . Moving about 25kts. Started 1210 worst over by 1222.
I estimate wind speed would have been 195km
spwill
Posts: 9907
Joined: Sun 29/06/2003 22:39
Location: Mt Eden Auckland
Has thanked: 839 times
Been thanked: 866 times

Re: Hobsonville Storm Damage Track

Unread post by spwill »

Looks like southwest wind damage at the end Kowhai Rd, Whenuapai ( near runway) yet NE wind damage showing along Puriri Road.
METMAN
Posts: 39
Joined: Sun 13/01/2013 21:15
Location: Auckland
Has thanked: 0
Been thanked: 0

Re: Hobsonville Storm Damage Track

Unread post by METMAN »

Image
Image

First pic Hobsonville Microburst
Second pic Albany Tornado
User avatar
NZstorm
Posts: 11333
Joined: Mon 10/03/2003 19:38
Location: Grey Lynn, Auckland
Has thanked: 342 times
Been thanked: 361 times

Re: Hobsonville Storm Damage Track

Unread post by NZstorm »

The top photo looks like a scud bomb over Hauraki Gulf. The bottom pic is the Albany supercell tornado . :smile:
User avatar
Nev
Moderator
Posts: 6216
Joined: Tue 07/03/2006 15:24
Location: Waiheke Island, Hauraki Gulf
Has thanked: 468 times
Been thanked: 1064 times

Re: Hobsonville Storm Damage Track

Unread post by Nev »

Re the first pic, the caption on TVNZ's West Auckland 'tornado' Photogallery reads, 'Fleur Heaton captured this photograph of clouds moving from the west out to sea over Orewa Beach, Auckland'.

I assume the second one is the Albany Tornado last May?

It would be helpful if you acknowledge the source of any images or data as per the forum gulidelines. :smile:
Locked