Hobsonville Storm Damage Track

[spwill]

A couple of photos, photo 1 taken near Carnegie Cres on the west side of the damage path shows trees lying in an east direction, photo 2 taken on Merton St on the east side of the damage path shows trees lying in a west/southwest direction. There are trees at the Bowling Club that have been blown over facing north. It will be interesting to map the wind damage across Hobsonville using my photos at some stage.

[METMAN]

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

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Radar1.JPG

Bow echo (winds) as defined by Dr Theodere Fujita is more of a mesoscale event similiar to a squall line (remember the exciting TV of yachts Whitbread finish hit by line squall North Head). He used it to define winds on a larger scale outside of microburst parameters. The line of winds maybe about 5km wide.

However microbursts can also display bow echo returns with cold inflow on radar. The definition would be in width of outflow which at Hobsonville is that of microburst.

[METMAN]

A couple of photos, photo 1 taken near Carnegie Cres on the west side of the damage path shows trees lying in an east direction, photo 2 taken on Merton St on the east side of the damage path shows trees lying in a west/southwest direction. There are trees at the Bowling Club that have been blown over facing north. It will be interesting to map the wind damage across Hobsonville using my photos at some stage.

Probably for strongest wind flow it is better to look at larger fallen trees. Even then then trees bending and gyrating with wind force and falling against others can give a false indication. I will post pictures of large fallen trees later

[Manukau heads obs]

Spwill,reminds me of now echo squall that hit
Us with littlr warning in the USA at night...when we had to pack up cameras real fast we thought
It was a rain wrapped tornado at first....debris flying off trees and all
Like some of the photos

[METMAN]

Trees fallen to SE direction near Wallace Inlet Hobsonville

[NZstorm]

Spwill,reminds me of now echo squall that hit
Us with littlr warning in the USA at night...when we had to pack up cameras real fast we thought
It was a rain wrapped tornado at first....debris flying off trees and all
Like some of the photos

That was a big squall line. It overrun us a bit quicker than we were expecting as it was night.

[spwill]

Trees have fallen to a southwest direction at the east end of Merton street, Hobsonville. This photo was taken about 38 Merton street.

Edit, this is on the east side of the the damage trail

[spwill]

My photos show trees on Wallingford Way/ Saint Georges Rd have fallen to the SE direction

Edit , this area is on the west side of the damage trail, there some damage on the western edge which points east.

[Cook]

It will be interesting to map the wind damage across Hobsonville using my photos at some stage.

It would be very interesting, spwill, if you could put arrows on a map that show the direction which trees, etc have fallen. I very much look forward to seeing one.

[METMAN]

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   

Edit: Amended error in temps & pressure.

The wind directions of these metars should point straight to the location of the microburst if it was present at that time. It began about 12:10 and I would expect the one minute WP AWS reports to start reporting a wind direction from about NE turning E becoming SE as system moved South. I can't explain the SSW direction of that gust. (Yet)

[spwill]

It would be very interesting, spwill, if you could put arrows on a map that show the direction which trees, etc have fallen. .

Yes Cook I will do this.

[NZstorm]

It began about 12:10 and I would expect the one minute WP AWS reports to start reporting a wind direction from about NE turning E becoming SE as system moved South. I can't explain the SSW direction of that gust. (Yet)

Considering the deep layer tropospheric flow was NW, the SSW 69kt observation was unusual and to me points to something more dynamic than a microburst.

Would it be possible to see the one minute data Metman?

[METMAN]

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   

Edit: Amended error in temps & pressure.

I suspect that 203 degree gust came from western book end vortice, associated with microburst bow echo, passing near WP AWS. On the western flank the flow would have been cyclonic. Rotating SE to S to SW to W to NW to N (so SSW fits)

[METMAN]

It began about 12:10 and I would expect the one minute WP AWS reports to start reporting a wind direction from about NE turning E becoming SE as system moved South. I can't explain the SSW direction of that gust. (Yet)

Considering the deep layer tropospheric flow was NW, the SSW 69kt observation was unusual and to me points to something more dynamic than a microburst.

Would it be possible to see the one minute data Metman?

I will ask, but metservice are currently using data for their own microburst investigation and probably will say no.

[NZstorm]

suspect that 203 degree gust came from western book end vortice, associated with microburst bow echo, passing near WP AWS. On the western flank the flow would have been cyclonic. Rotating SE to S to SW to W to NW to N (so SSW fits)

A bookend vortex of 69kts + is likely a tornado.

The Met Service radar 55km away and would not detect a bookend tornado.

[spwill]

1. tree debri fell forward both sides of track.
.

METMAN, Did you do the survey of the tree damage to arrive at the above conclusion ?

[METMAN]

1. tree debri fell forward both sides of track.
.

METMAN, Did you do the survey of the tree damage to arrive at the above conclusion ?

Yep. I Took the photos

[METMAN]

Hi NZStorm,
Have attached MetService Auckland Weather Radar 06Dec 0007 NZST and 0015 NZST in case you haven't seen them. I am no expert but I see no sign of tornadoes.

[spwill]

Yep. I Took the photos

What direction range do you consider is forward of the track with the tree damage ?

[spwill]

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

[METMAN]

Yep. I Took the photos

What direction range do you consider is forward of the track with the tree damage ?

I estimate the storm swathe direction from 330 degrees T
Most of uprooted trees lying about 150 degrees T on both sides of swathe.

[METMAN]

Just been looking at midday upper air sounding from Whenuapai on 6th Dec. I was looking for shears (dir or speed) but there is nothing (released at 1030 probably too early for the event.) Unusually little directional variation 310 to 320 degrees, wind speeds gradually increasing to quiet strong (140kts) at 200 to 150 hPa.
Does however show a microburst feature of a dry region (RH30%) from 600 to 450 hPa. I will try to post a tephi example of a microburst dry region later

[METMAN]

[METMAN]

A microburst tephigram showing example of dry area

[spwill]

Some trees have fallen back in a west /NW and North direction.
There is a convergent look to the damage trail through Hobsonville, does this fit Microburst ?