Thunder risk Tuesday 21st to Thursday 23rd May

[NZstorm]

base of cb.

[NZstorm]

another pic

[Tornado Tim]

Awesome photo's guys well done

[spwill]

My best lightning shot and a couple more shots. I followed the storm to Flat Bush, gusty winds and hail there.

[NZ Thunderstorm Soc]

Lovely shots
Heavy rain here today this morning and this evening. Very isolated lines and we seem to be copping it.
More in my Blog at 10pm.

[Brassnz]

Sensational photos! Well done all.

[GreggWard]

Awesome photos you guys!

[Tornado Tim]

Video of the storms in Auckland from nz herald via weatherwatch: here

It shows a very nice negative CG with a positive CG well away from the rain shaft. Quite impressive

[03Stormchaser]

Enjoying the photos

[Richard]

Yes good shots alright

[Tornado Tim]

Looking at tomorrows forecasted sounding I would agree with Metservices T-storm outlook for the Waikato.

However I think they may need to add a low risk of a Severe Storm with general moderate risk as several Index's are indicating the possibility of severe conditions if any storms do form such as SWEAT.

A little lightning activity occurring out on west coast, but not as much I was expecting…. Perhaps it may develop a little later as better air gets dragged in overnight.

Valid to: Midnight Wednesday 22 May 2013
Issued at: 9:26pm Tuesday 21 May 2013

A small intense low embedded in the unstable northwesterly flow is expected to affect the far north Wednesday afternoon and evening. There is a high risk of thunderstorms, and a moderate risk of severe thunderstorms with downpours,strong wind gusts, 90-110 km/h, 10 to 20mm hail in Northland and Great Barrier Island as indicated on the chart. Localised small tornadoes are also possible.

In other areas exposed to the moist unstable northerly and northwesterly flow there is a moderate risk of thunderstorms with heavy rain, strong wind gusts and hail as indicated on the chart.

No other areas of severe convection or thunderstorms are expected.

[Michael]

how you dump the shot off the video,its shows a blank here.

Some shots pulled from my vid's this afternoon.

[Nev]

Video of the storms in Auckland from nz herald via weatherwatch: here

It shows a very nice negative CG with a positive CG well away from the rain shaft. Quite impressive

I see the original video was shot by Geoff Mackley and Bradley Ambrose.


Speaking of the NZ Herald and WW, I was a little astonished by this claim yesterday…

'Waterspouts form over Manukau Harbour'

Water spouts -the name given to tornadoes over water - could cause winds averaging between 120 - 200km/h, Mr Duncan said.

"Out at sea they can look a lot more dramatic because they suck up all the water."

Although the decreased air pressure from some of the most intense tornadic type of waterspouts can actually raise the water level by as much as half a metre, they don't actually suck up water into the into the main funnel cloud itself. The water droplets seen in the funnel cloud are formed by condensation.

[Manukau heads obs]

there is spray kicked up though on the water surface


the NW wind change that created this very active CB line I reckon actually was enhanced by an outflow boundary from decaying CB's in behind (you could see the spent anvils out to the west )
once the whole line went through here the wind returned to being a NE

[NZstorm]

The surface NE is always great for storms in these set ups. Today looks NNW.

A robust shortwave in the North Tasman moves onto Northland this afternoon. Looks like the best forcing will be over Northland so thats were most of the lightning activity should be. However Auckland/Waikato are in the frame, just have to see what can eventuate.

[Manukau heads obs]

more photos sent to me by a local resident (Big Bay)
stunning!
it was picking up mud off the mudflats!
lasted 15 minutes or so!

[spwill]

A photo taken from Mt Roskill looking across the Manakau about or near the time the spouts occured, shows how unstable the weather was yesterday afternoon. 2nd photo near Blockhouse Bay

[Orion]

Those waterspout pictures are remarkable!

[Nev]

Agree, those waterspout pics posted by Brian are undoubtedly among the best I've seen so far...

[Nev]

I see this morn's outlook has extended the moderate-risk of Severe T-Storms to Akld for this arvo and early evening…

MetService - Severe Thunderstorm Outlook

Valid to: Midnight Wednesday 22 May 2013
Issued at: 8:58am Wednesday 22 May 2013

A low over the Tasman Sea is moving slowly towards the centre of New Zealand. Unstable conditions exist over much of the north and west of the North Island and northern South Island.

As a trough moves over Northland, most of Auckland and northern Coromandel Peninsula this afternoon and early evening there is high risk of thunderstorms occurring, with a moderate risk that these thunderstorms could become severe. With the thunderstorms there is likely to be localised heavy rain with intensities of 10 to 25mm per hour, strong wind gusts of 90 to 100 km/h, hail of 10 to 20mm diameter and possibly a few small tornadoes. In severe thunderstorms,wind gusts may exceed 110 km/h and hail larger than 20mm in diameter is possible.

A moderate risk of thunderstorms also exists over southern areas of Auckland and the Coromandel Peninsula, Waikato, Waitomo, northern Taranaki and western Bay of Plenty this afternoon and early evening and in eastern Bay of Plenty and northern Gisborne tonight. If these thunderstorms occur they are likely to be accompanied by localised heavy rain of 10 to 25mm per hour, strong wind gusts of about 90 km/h and hail with diameters between 10 to 20mm. In Taranaki, the thunderstorms might develop just before midday and there is a slight chance of small tornadoes there as well.

This evening there is also a moderate risk of thunderstorms over northern Nelson and the Marlborough Sounds. Here localised heavy rainfall of 10 to 25mm per hour, strong wind gusts of 90 km/h and hail of 10 to 15mm diameter is possible.

A low risk of thunderstorms exists just outside the above areas during the day.

No other areas of thunderstorms or severe convection are expected.

MetService TS Outlook - Is. May 22, 0858am.png

[Manukau heads obs]

thunder heard here, distant , from CB out to me west
very blown off anvil top

[Tornado Tim]

Speaking of the NZ Herald and WW, I was a little astonished by this claim yesterday…

'Waterspouts form over Manukau Harbour'

Water spouts -the name given to tornadoes over water - could cause winds averaging between 120 - 200km/h, Mr Duncan said.

"Out at sea they can look a lot more dramatic because they suck up all the water."

Water Spouts are not simply tornadoes over water, they have the same mechanism as a Landspout and do not carry the supporting mesocyclone to call them an actual Tornado.
It's extremely frustrating when people mislead the public with false statements.

Most tornadoes we get in New Zealand are actually Landspouts, to the untrained eye they look like a Tornado but they are much weaker as they carry no upper level support from a mesocyclone.

The statement that waterspouts carry winds in the range of 120-200km/hr is also false depending on the type of waterspout. Water carries significant weight and most waters spouts are less than 63 knots. Reference
However if we are talking about "Tornado's over water" then thats different as they can be much stronger, but there was no indication that the storm carried a mesocyclone so the statement is technically false.

Although the decreased air pressure from some of the most intense tornadic type of waterspouts can actually raise the water level by as much as half a metre, they don't actually suck up water into the into the main funnel cloud itself. The water droplets seen in the funnel cloud are formed by condensation.

I believe that need's to be debated as there have been many occasions where fish,frogs etc have been picked up by Tornadoes over water.
I somehow doubt fish would get "plucked" out of the water from a waterspout without any supporting water around them.
This also contradicts what we see when we look at a waterspout on the sea surface such as spray etc.

[Weather Watcher]

Nice photos of the waterspout.

I think some of the comments comparing waterspouts and tornadoes are misleading and not correct. While both waterspouts and tornadoes occur in environments with strong low-level buoyancy, waterspouts generally occur in a low shear environment, while tornadoes generally occur in high shear environments. For this reason, I don't believe waterspouts and tornadoes are the same thing. Also, regarding the wind speeeds associated with waterspouts, these often quite low, compared to the higher speeds assocated with tornadoes. There was a video on one of the TV channels of the waterspout over Waitemata Harbour last year where a boat went through the base of the waterspout a couple of times, and the winds were actually quite light.

PS. I've just noticed Tim has pretty much said the same thing, but I'll post this comment anyway.

[Area51]

Met advising large active CB drifting south from Kaipara and forecasting large hail.
Don't often hear that advice given to aircraft as was this case!

[Tornado Tim]

Quite a nice cell to the west of New Plymouth: - up to 60dbz in sections of the cell, certainly producing hail.