05/11/09 DISC: New Zealand

[Willoughby Owen]

Unlike the US , there seems to be no shortage of strong upper troughs amplifying over New Zealand now during late Autumn.

May 11 - Bay of Plenty on the North Island's ENE coast.

A strong upper trough (500mb temps were a rocking -31C and approaching) coupled with days of a persistent belt of sub-polar lows regenerating up the Islands brought quite a bit of instability over the Tasman Sea and Pacific where waters are relatively warm (16-20C) this time of year.

Vortex of the low (990mb) just off the west coast of the North Island can easily be seen embedded with a thunderstorm there. Turned out to be a highly supportive environment for tornadoes and one wonders if this storm that smashed through Papamoa just east of Tauranga with 1 in 30 year hail, was supercellular in nature and formed a waterspout or tornado? It developed just off the beach. I'd be curious to know what some experts think.

Another view,

Youtube video of storming hail and distant twister (worth a watch) Not sure if it's the same twister above.
http://www.youtube.com/watch?v=VEDog1KC9IM

And for a bit of fun:
http://www.youtube.com/watch?v=yx31Nen8NiA

Flooding hail!

NOAA-19 satellite at 3.24PM, near when the storm hit -- Papamoa is directly east of the low vortex on the other side of the island:
http://satellite.landcareresearch.co.nz/noaa-db/2009/may/qd11059.jpg

Modelled Papamoa sounding based on GDAS,
http://imgur.com/nir2z.gif

NZ is setting itself up for it's coldest May on record based on current model trends as an omega block in the SC Pacific Ocean continues...
( http://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_sh_anim.shtml )

I'd be interesting to hear your thoughts re if it was a supercellular tornado or waterspout.
Relevant news article: http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10571661

Thanks
Willoughby

 

[Isaac Pato]

Wow, that is amazing stuff. I'd say that the storm looks like a supercell to me. You can see the RFD wrapping behind the tornado in those pictures. From the model sounding, it looks like the environment was sufficiently sheared to support supercells (winds backing to the NE at the surface, shifting to the NW higher in the column, as well as sufficient speed shear).

 

[Michael O'Keeffe]

That is clearly a tornado with a classic RFD cut as seen in the second picture and the size of it makes me believe it is one. Well I guess you would call it a tornadic waterspout. Pretty neat stuff! I am incredibly interested in tornadoes outside the Great Plains.