NI - low pressure troughs, fronts 4 -6 May

[Cyclone Tracy]

I think this needs it's own thread. Multiple upper, surface troughs along with frontal boundaries over the next 48 hours moving across the NI. Cold convection with hail, thunder, downpours and an unstable flow in the mix. Possible waterspouts also with the sea surface temps still around 18 to 19c in the Hauraki Gulf combining with 500 hPa -25 to-30c on Tuesday.

Just had a quick downpour on that first trough around 12pm.

[wre1991]

Thunderstorm passing by Waihi, few rumbles nothing too exciting yet.

[Cyclone Tracy]

Radar looking more lively now. Heavy shower here, no thunder heard yet but a CG appearing on Blitz north of here.

[Awhituobs]

good thunderstorm just gone through this area
(we could see the flashes here)

[spwill]

A gusty heavy shower here now with some small hail.
Distant lightning flashes observed out west Auckland way a little earlier.

[tornado]

had one downpour here today. saw a flash to my south before. hoping for thunder /hail

tommorow also a risk. yay.


hail now first time this year it hailed here hopefully a few rumbles may evolve tonight or tommorow

[Cyclone Tracy]

A couple of short sharp downpours with that batch. 8mm so far today, so May is ticking along. Another surface trough is powering towards the upper NI in the Tasman, should move through in the early hours.

[Vertigo]

I see a cell inbound for Helensville with a hook signature! Has maintained it the last few radar passes..

Screenshot from 2020-05-04 23-29-28.png

[NZstorm]

Hi Vertigo, will not be a supercell as it looks too big. Supercells in these cold sheared set ups would be quite small and hard for the radar to detect unless they are close to the radar.

Next front with a thunder risk is due across the Auckland area middle of the day. 500mb temperature is -24C so cold. Modelled dp is 11C which is enough. Daytime heating would also add to the instability mix! With air this cold, the precip in storms will be hail.

I see lightning starting to occur in that front out in the Tassie now!

[tornado]

hope this front makes it. been so long without a decent overhead thunderstorm.

heres this mornings outlook for today.

Valid to: Midnight Tuesday 5 May 2020

Issued at: 9:02am Tuesday 5 May 2020

An unstable showery airmass affects central and northern New Zealand today.

There is a moderate risk of thunderstorms from late morning for Auckland, Waikato, Waitomo, Taumarunui, Taranaki and Whanganui; while there is a moderate risk of thunderstorms from Manawatu to Wellington, including Wairarapa and also Nelson and inland Marlborough from this afternoon. These thunderstorms are likely to bring localised heavy rain with intensities of 10 to 15 mm per hour, hail and for areas from Auckland to Whanganui strong wind gusts.

A lower risk of thunderstorms covers most remaining areas of the North Island and the upper South Island.

No thunderstorms or significant convection expected elsewhere in New Zealand during this period.

image.png

[GraemeWi]

Thunder arriving into West Auckland with the leading edge now

[Cyclone Tracy]

A few more mm's locally with the lunchtime front. A few coldies currently bubbling in the Tasman on the water vapour image. GFS 18Z showing -27c @500 hPa around Auckland later tonight when another surface trough moves through, TT value near 57. Precip might be a bit icy.

[tornado]

kapiti had a waterspout turned landspout today destroyed a chickens coop.


hail and thunder now. yay my first overhead thunder clap of the year.

[Cyclone Tracy]

Good to hear.

Water vapour image is bubbling ahead of the trough. Using EC 00Z as a guide, here are the 3 hour projected positions of the trough over the current water vapour image. The uppers are nice and cold.

[Awhituobs]

we did get a brief hail shower around 8pm

[spwill]

A non event here today but have a heavy shower with hail here currently.

[Cyclone Tracy]

Distant thunder, blitz showing to my SE

[spwill]

Some distant lightning/thunder observed here.

[tornado]

had a thunderstorm here after 10pm last night. some good bright flashes and good close rumbles of thunder.
was accompainied by a hail shower. was about time for one to make it through i reckon.


this system was not really a bust for me. 68mm of rain from sunday ,monday and yesterday. was a good set up. the drought couldn't stop this one for sure lol. was a really good heavy rain event for us for sure.

[David]

Apart from some random distant rumbles late yesterday evening, nothing much here overnight, 2mm of fairly gentle showers. Not complaining though, 71mm this month already

[Cyclone Tracy]

Short intense showers, distant rumbles last night. An extra 13mm with the fronts and troughs to make it 53mm for May so far. Almost doubled the first 4 months rain in 5 days.

[Awhituobs]

we have caught up a bit on the city for rain as we did well out of the shower with 11mm yesterday, 32mm for May so far now, so great