Low pressure system eastern South Island 18/3/25

[Razor]

We've already tipped out 35mm here in Lincoln Uni, 15mm of that in the past hour. Winds have eased for the moment

[Cantab03]

Only light to moderate rain here in chch. Radar showing it a lot heavier than it actually is.

[Razor]

Very serious surface flooding around here and the rain intensity is only increasing. Big problems on the roads

[Storm Struck]

What is the warning threshold for MS? It's deteriating very quickly out there now with lots of surface flooding.
Also seen recent footage past 20 minutes of waterfalls over roads on Banks Peninsula, some roads are literally impassable.

Light rain has now turned to heavy here as the low continues to slowly develop, wind gusts have been relatively strong at times nothing too serious in terms of wind yet.

[Razor]

I'm in Motukarara under the purple on the radar. Can confirm it's as intense as it looks. Can't believe there's not a rain warning, things are escalating rapidly here

[Razor]

Akaroa Highway is compromised north of Kaituna. Flash flooding

[Bradley]

I'm in Motukarara under the purple on the radar. Can confirm it's as intense as it looks. Can't believe there's not a rain warning, things are escalating rapidly here

70mm in Motukarara in the last 3 hours, incredible. I just don’t understand how a few hours out from the event EC got it so, so wrong

[TonyT]

I'm in Motukarara under the purple on the radar. Can confirm it's as intense as it looks. Can't believe there's not a rain warning, things are escalating rapidly here

70mm in Motukarara in the last 3 hours, incredible. I just don’t understand how a few hours out from the event EC got it so, so wrong

There's wide mesoscale variation with this system. For example, by contrast with the above, I'v e had 12mm here in Amberley, and there are parts of the city with under 20mm so far. You could argue the GFS with its 70mm estimate was also "so so wrong". The reality is, much of the weather we are currently experiencing is slipping between the gaps (you could also say through the cracks!) in the "net" of the global scale models.

[Razor]

70mm in Motukarara in the last 3 hours, incredible. I just don’t understand how a few hours out from the event EC got it so, so wrong

There's wide mesoscale variation with this system. For example, by contrast with the above, I'v e had 12mm here in Amberley, and there are parts of the city with under 20mm so far. You could argue the GFS with its 70mm estimate was also "so so wrong". The reality is, much of the weather we are currently experiencing is slipping between the gaps (you could also say through the cracks!) in the "net" of the global scale models.

To be fair the event is still ongoing and becoming more widespread. Many gauges will be tipping out 50-100mm by midnight

[TonyT]

The pressure gradient has tightened up further. Winds at LeBons are now 38 knots (gale force).

Screenshot 2025-03-18 at 7.37.51 PM.png

[Dean.]

Heavy rain falling here 32mm so far.
Metvuw (GFS) model is pretty accurate in my opinion,especially for Canterbury.

[Karliosis]

70mm in Motukarara in the last 3 hours

Think that was the Te Oka station, Motukarara shows 32.4mm for the 3-6pm period, Te Oka shows 65.2mm in the same time period. An additional 13mm in the hour to 7pm takes the total there to 78.2mm in 4 hours

Heavier rain now moving into south Christchurch. Wind hasn't increased since my earlier posting, staying fairly stable as fresh to strong.

[Razor]

70mm in Motukarara in the last 3 hours

Think that was the Te Oka station, Motukarara shows 32.4mm for the 3-6pm period, Te Oka shows 65.2mm in the same time period. An additional 13mm in the hour to 7pm takes the total there to 78.2mm in 4 hours

Heavier rain now moving into south Christchurch. Wind hasn't increased since my earlier posting, staying fairly stable as fresh to strong.

Kaituna Valley is approaching 100mm, just down the road from Motukarara. I won't be surprised if Little River and Akaroa are cut off tonight

[TonyT]

Next up, the Kaikoura coast.

[Storm Struck]

Fairly sure I read that SH75 is now closed from Tai Tapu due to flash flooding.
I know I said tie down your trampoline but the BBQ ended up sailing across the patio almost next door with a gust earlier .
Don't fancy sharing that with the neighbour.

Not too often we get a low park itself up over the city and peninsula and develop like this.

[Razor]

State Highway 75 Motukarara to Little River is now closed by deep floodwaters accross the road in several locations

[Bradley]

I think a warning, at least for the plains and not Chch city is now in order…

[Razor]

I think a warning, at least for the plains and not Chch city is now in order…

Maybe 5 hours ago....

[Razor]

This was just outside Lincoln at 5pm it was torrential and prolonged

[Richard]

Quite a range of rainfall between each end of the Amuri basin, 24.8mm here while Waiau had 58.6mm. The Cheviot page is not working.

[Razor]

Our Halswell gauge tipped out 49mm, Lincoln Uni got 62mm

A selection of the highest recordings at Environment Canterbury gauges for the event, reflecting a widespread event from South Canterbury to Hurunui with most of the falls inside a 6 hour period- which I note would meet the Metservice Heavy Rain warming criteria:

Akaroa Highway (Cooptown) 117.4mm
Akaroa Niwa 85.6m
Townshend 84.5mm
Kaituna 82mm
Stavely 76mm
Mt Somers 75.5mm
Whitecliffs 71.6mm
Rakaia Gorge 71.5mm
Taitapu 69.5mm
Mt Hutt Station 65.5mm
Hinds 65mm
Coopers Knob Port Hills 63mm
Hurunui Bridge SH1 61mm
Fox Creek Okuku 59.5mm
Bowenvale Christchurch 58mm
Blandswood 57mm
Ashley Gorge 56.5mm
13 Mile Bush 55.5mm
Taumutu 52.5mm
Okuku 50mm

[TonyT]

48mm Charing Cross
30mm Amberley
20mm Chch Aero

[Richard]

Razor - do you have the rainfall data for stations on the N and NE side of the peninsula, looked to have been some what sheltered going by the radar yesterday

[Razor]

It did its usual rainshadow thing as Tony T noted yesterday during the event. As has been a repeated pattern this year a particularly active area is from BP and Te Waihora /Lake Ellesmere across Taitapu and into the south western suburbs of Christchurch, by the time you get past Cashmere hills/ Bowenvale it peters out.

It seems Prebbleton had the worst flooding I would be interested to see a gauge there

https://www.ecan.govt.nz/data/rainfall-data/?loc=N

[Storm Struck]

The lake affect on enhanced rainfall within that narrow strip going forward is a key part of the takiwā planning for Biodiversity.
A project I am currently a part of alongside SDC.
Climate is something we will be strongly looking at.

The Heathcote was flowing dirty and high this morning but not breaching.
Wind was quite strong at times overnight but overall I think Windy nailed this aspect better compared to the surface moisture.