NZ Weather Forum

Very heavy showers have been passing through over work this afternoon since 1pm before that was lighter rain or drizzle, easily 25+mm by now with a lot of surface water around.
Southerly gusts abit stronger now.
I can see the main slow moving heavy band coming in off the coast on the radar, this will bring some healthy totals tonight from Ashburton northwards and especially for Kaikoura and Banks Peninsula.

The story made the main news here in the UK and the reports concentrated on the flooding aspects of both Gabrielle and the very wet weather in the preceding month.

https://www.bbc.co.uk/news/world-asia-64645510

Simon Culling wrote: ↑Wed 15/02/2023 19:37 The story made the main news here in the UK and the reports concentrated on the flooding aspects of both Gabrielle and the very wet weather in the preceding month.

https://www.bbc.co.uk/news/world-asia-64645510

Northern NZ has not seen a Summer like this one in living memory. The Auckland flash flood event two weeks ago was called a 1-in-200 year event by Niwa. Cyclone Gabrielle bringing more widespread significant rain and strong wind + storm surge to some areas.

I wonder..... could it have been something to do with that pesky Tongan volcano eruption?

The upper trough crossing the upper North Island tomorrow looks particularly cool for February . GFS showing good instability numbers particularly south of Auckland and over eastern Northland for some heavy shower and thunderstorm development. Should be plenty of heating tomorrow. Auckland region will probably lack convergence but will see how the day unfolds tomorrow..

Comms outages for Northland. (Roads and Power are a whole new set of maps..)

shovelopikis wrote: ↑Sun 12/02/2023 06:30

NZ Thunderstorm Soc wrote: ↑Sat 11/02/2023 23:26 r
Hope this won't put dampers on the Art Deco Festival in Napier what my wife and I are coming up for next WE

We are heading over on Thursday... Not sure if our accomodation will be still standing or floated away given these numbers, but the wind will be a major concern to western regions


... And now it looks like some areas around East Cape are predicting half a metre of rain!!

I see it was cancelled. Makes sense owing to the circumstances.

James wrote: ↑Wed 15/02/2023 22:01 I wonder..... could it have been something to do with that pesky Tongan volcano eruption?

I keep thinking of this. but no official reports that I have seen or read, mention the eruption having anything to do with the current weather that the La Nina weather is delivering us. I think it does have an effect especially with these so called atmospheric rives from because of all the water vapour that was released from the volcano during the eruption.

James wrote:I wonder..... could it have been something to do with that pesky Tongan volcano eruption?

Doubt it. If it were, why has rainfall concentrated on NZ north island. If it were the case, how is it possible to bullseye on us? It just doesn’t stack up. If it impacted the weather in the southern hemisphere you would expect to see similar abnormalities across the southern hemisphere. Which we don’t see. Heck a couple hundred km to the east of NZ has been basking in high pressure all summer.
To me it’s narrow minded to assume because your getting wetter than normal the whole Southern hemisphere is. It clearly isn’t the case.
When you consider the winds and temperature at the altitude the water got lofted too, it’s near impossible for it to create increased rainfall anywhere, let alone to bullseye on north island.

When we see changes right across the southern hemisphere or even the world then we can say the volcano has had an impact.


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Just doing some reading on the Hawkes Bay website and looking at river levels. Seems the Esk valley has a catchment that is prone to short sharp flood events like the ones in 1938 and 2018.

The Esk river flow at Waipunga Bridge

3:45am Monday 13/2/23 was 7.29 Cumecs (7,291 litres a second)
3:45am Tuesday 14/2/23 was 1787.4 Cumecs (1,787,396 litres a second)

A 24,415% increase. That is absolutely mind boggling for me, no wonder most of the residents had merely minutes to try and evacuate. It rose in level just over 9 Metres in around 20 hours.

https://www.hbrc.govt.nz/environment/river-levels/

There have been unprecedented floods in Oz as well for the past year. I have read reports that the eruption has increased the atmospheric temperature by 1.5 degrees (NASA) I think. Forget about farting cows, this was the biggest explosion for over a thousand years. You don't hear about it (but news in Oz) because it does not fit the agenda. It makes me so angry. James Shaw is a drongo!

Hardly a bullseye over the North Island. We've been having these atmospheric rivers over NZ and Australia for the past year [expletive deleted]!

Napier a real mess. Especially the outlying areas.

James wrote: ↑Thu 16/02/2023 09:42 Hardly a bullseye over the North Island. We've been having these atmospheric rivers over NZ and Australia for the past year [expletive deleted]!

And every La Niña season. Hunga Tonga has certainly impacted the atmosphere, but Nina was already shaping up to be significant again before the eruption, then reached a strongest in over one hundred years state, so was always going to bring a summer of deluges and heatwaves. You can't have a major climate driver reach that level of intensity and not get major downstream impacts.

It will be interesting to see if Hunga Tonga has a discernible impact once (if) we transition to Nino. I suspect it might.

Mod Note: Can we please keep this civil folks.

Perhaps we could also do with a separate thread re the Tonga eruption versus any possible effects on the climate, rather than pepper multiple threads with the same comment(s)?

Sadly I think the death toll has some way to climb yet

Apologies. Makes me so cross and sad. I will say no more.

Last week when things were already looking serious for this week, I took this grab of the GFS model for 3am on the 14th Feb. Crazy how accurate it ended up being in terms of the centre of the system and the onshore flow on the east coast.
We have a family member who has lost everything in the Gillian’s Road area of Pakowai. Both the Ngaruroro and Tutaekuri rivers broke their banks, and water VERY quickly flooded their property. They made it out with nothing but their cellphones and the old Ute, and had to drive through waist deep water to escape. That was about 840am. The emergency alert to evacuate the area was issued at 1030am. Helicopters were already plucking people from roof tops by then. I think the scale and speed of the event caught everyone totally off guard.
The techie side of me asks where were the automated alerts from river sensors when the predictions had been for such heavy rain. It would not have prevented the damage, but would have saved lives and people would have had more time to get out with at least some belongings.

Possibly a communications problem with the telemetry. I know that Horizons RC lost communications with their river level recorders in the Manawatu catchment during this event and so were flying blind when it came to predicting flood peaks further downstream.

Patoka - Inland Hawkes bay. We’ve been cut off since Tuesday night no power, both bridges are gone (Rissington & Dartmoor) All cellphone towers are down (we’ve got Starlink and a generator) We’ve just managed to start to clear the roads around us today to access more people around us. The place is just devastation, slips everywhere, pretty much every bridge gone or unusable. It’s going to be weeks before we have access to town at this stage. Thankfully we’ve been getting regular supply drops over the last few days by helicopter.

We had 440mm over 24hours and around 200mm between 12am - 6am Tuesday morning.

I've just noticed this Auckland council site at Piha showing 357mm between 8am on the 13th and 8am on the 14th
https://environmentauckland.org.nz/Data ... AR/2023/02

This would certainly explain the major flooding and slips they are dealing with over there. I don't remember seeing the rain so much more intense over there on radar at the time interestingly (much of Auckland got 100-150mm).

The pre-event data looks all good so no reason to doubt the accuracy of the data. Truely astonishing!

David wrote: ↑Fri 17/02/2023 12:47 I I don't remember seeing the rain so much more intense over there on radar at the time interestingly (much of Auckland got 100-150mm).

The radar beam can be quite strongly attenuated by reflections (rain) between the origin and the target. So radar will always tend to underestimate distant rain rates when there is also rain closer.

What caused this 90 degree turn?
It didn't stall at that pivot point if I'm correct, I know when cyclones stall they can make a sharp re alignment but I'm interested to know the how or why behind it

David. I did notice the rain just off the west coast of kaipara and south was very intense on the radar. That rainfall doesn’t surprise me.


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TonyT wrote: ↑Fri 17/02/2023 13:27

David wrote: ↑Fri 17/02/2023 12:47 I I don't remember seeing the rain so much more intense over there on radar at the time interestingly (much of Auckland got 100-150mm).

The radar beam can be quite strongly attenuated by reflections (rain) between the origin and the target. So radar will always tend to underestimate distant rain rates when there is also rain closer.

yep, often noticed that here given the distant we are to the Canterbury Rakaia site, but only with during lower level cloud based events, the flat layout of the plains has surely to help extend its range, but here it needs a higher cloud base.