Nth'n North Island T-storms - July 7-8

[NZstorm]

I see there has been a thunderstorm over the top of Northland last hr on the front. Front reaches Auckland area early morn.
The front will be over BOP/Waikato tomorrow before moving north again according to gfs.

[NZstorm]

Lightning thunder observed just now!

[spwill]

Distant thunder here, some heavy showers last hr.

Some distant lightning flashes N/NW last 5 mins.

[spwill]

Thunderstorm near here now, the odd flash and rumble

[littleheaven]

House-shaking thunder in Glenfield. Car alarms going off all up and down the street.

[Nev]

Yeah, what a spectacular storm - continuous thunder and lightning here!

[spwill]

No chance of sleep with this weather, thunder/lightning for central Auckland as well, I think main storm cell to the N/NE

[jamie]

Getting thunder here now as it moves closer. Been seeing lighting for past 30 mins.

[Nev]

Best lightning show here for a while - lasted for 2-3 hours.
Couple more tracker grabs…

[David]

11mm moderate rain overnight, was surprised to get woken by thunder around 1am given the low risk that was forecast

[NZstorm]

The lightning was all in the clouds here so i went for a drive east and had a close CG at Pakuranga.
Thunderstorms were elevated.
25mm here for the event.

[Nev]

Thought this unexpected T-storm event may as well have its own thread.

I see Whangaparaoa was gusting to 102 km/h last night.
17mm here since yesterday.

[NZstorm]

The unstable lapse rates and subtropical moisture should have alerted us to a stronger event.

[spwill]

Much of the lightning here was out to the north and east, overhead flashes would have been in the anvil cloud.

There must have been some good rainfall for some eastern coastal parts north of Auckland city which were under the development.

[David]

Much of the lightning here was out to the north and east, overhead flashes would have been in the anvil cloud.

There must have been some good rainfall for some eastern coastal parts north of Auckland city which were under the development.

Yep, looks like Leigh was under a line of torrential rain when I checked the radar loop at 1.30am. Would not be surprised if they got >50mm in 2 hrs there.

[Nev]

Looks to be quite a few east coastal sites north of Akld recording around 50-60mm for this event.
I see Whangaparaoa recorded 26mm in the 2 hrs to 2am - total 38mm.

Here's another lightning map from NIWA - 1600 'strikes' over the Auckland region in 4 hrs.
I'm guessing less than 10% of those are CG's...?

[GraemeWi]

A local monitoring site in West Auckland - http://aklc.hydrotel.co.nz/hydrotel/cgi ... tchment=28 - recorded about 76mm for the event which ties in with what I had in the rain gauge this morning (70mm). So disappointing I slept through it!

44mm fell between 0:44 and 2:45

The local river peaked a few hours later around 4:30am @5.1m

[spwill]

I took some video of the storm last night but it was just lightning flashes here so I won't bother posting.


Some nice towers visible over Coromandel way currently.

[spwill]

Mangawhai Heads is showing 65mm for yesterday, that area was in the firing line for the Cbs.

[NZstorm]

I have taken the forecast sounding from Thursdays midday run of gfs, for the North Auckland area midnight Thursday.

CAPE marked in yellow. Deeply unstable air mass but with low CAPE 350j/kg. Significant moisture PW 27mm.

I suspect the very strong NE you get in the outer gulf was being lifted and enhancing the lift into the Cb. Orographic factors would come into play as well.

[Nev]

Yes, interesting to see how that Cb development seems to have mainly favoured an area from about Warkworth/Kawau to Akld over a period of about 5-6 hours, peaking around 12am-1am. I think surface winds were initially more ENE going by MS's sites? Strong ENE'ers tend to get funnelled through the Colville Channel and can create a river of wind across to the Whangaparoa, which might be a factor? There radar also shows a few red patches heading down from the NNW, which might get some extra orographic lift from the ranges south of Wellsford.

I've put together an hourly time-line of radar images and of the Blitzortung CG's that might be of interest (note: red shows the oldest CG's during that hour)…

Blitzortung NZ comp. - Jul 7-8, 9pm-3am.png

MetService Ak radar comp - Jul 7-8, 10pm-3am.png

[NZstorm]

Thanks for the charts Nev.

Looking probable the low level jet over the Hauraki Gulf was the trigger for the storms.