Heavy Rain event West Coast/ South Island 9-12 April 2024

[Razor]

Thought I'd start a new thread as it looks like monsoon season is about to descend on the West Coast in particular but plenty of spillover also.

[Razor]

MS Orange warning, wouldn't be surprised to see it turn Red warned today

Severe Weather Warnings
Significant heavy rain for the west of the South Island, and strong northerly winds

A front is expected to move northwards over Fiordland on Tuesday, and become slow moving in Westland during Wednesday and Thursday. A humid north to northwest flow precedes the front, and is expected to bring periods of heavy rain to Fiordland and Westland, and strong north to northwest winds to Fiordland and the Canterbury High Country.

Watches and warnings are in force for heavy rain and severe gales. This is expected to be a significant heavy rain event for Westland, with potential for an upgrade to a Red Warning over the coming days. However, there is some uncertainty with the movement of this front, and the placement of heaviest rain may change.

People are advised to keep up to date with the latest forecasts.

Heavy Rain Warning - Orange

Impact: Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Area: Westland District south of Hokitika

Period: 57hrs from 9am Tue, 9 Apr - 6pm Thu, 11 Apr

Forecast: Periods of heavy rain. Expect 600 to 800mm to accumulate about the ranges, and 200 to 300mm about the coast. Peak rates of 20 to 30 mm/h about the ranges. This is a significant heavy rain event with the potential for upgrade to a Red Warning.

Area: Headwaters of Canterbury Lakes and Rivers south of Arthurs Pass

Period: 50hrs from 3pm Tue, 9 Apr - 5pm Thu, 11 Apr

Forecast: Expect 400 to 600mm about the main divide, and 200 to 300mm within 15km further east, especially south of the Rakaia River. Peak rates of 15 to 25 mm/h.

Area: Headwaters of the Otago Lakes and Rivers

Period: 23hrs from 9am Tue, 9 Apr - 8am Wed, 10 Apr

Forecast: Expect 200 to 300mm about the main divide, and 100 to 150mm within 15km further east. Peak rates of 15 to 25 mm/h. Heavy rain is expected to return later on Wednesday and become more widespread through Otago. This warning may be extended, or a Watch issued, closer to the time.

Area: Fiordland about and north of George Sound

Period: 23hrs from 4am Tue, 9 Apr - 3am Wed, 10 Apr

Forecast: Periods of heavy rain. Expect 150 to 250 mm of rain. Peak rainfall rates of 20 to 30 mm/h. Heavy rain is likely to return later on Wednesday and this Warning may be extended, or a Watch issued, closer to the time.

Heavy Rain Watch

Area: The Grey District, and Westland District about and north of Hokitika

Period: 48hrs from 6pm Tue, 9 Apr - 6pm Thu, 11 Apr

Forecast: Periods of heavy rain, and amounts may approach warning criteria.

Area: Fiordland south of George Sound

Period: 17hrs from 4am - 9pm Tue, 9 Apr

Forecast: Periods of heavy rain, and amounts may approach warning criteria. Heavy rain may return later on Wednesday and this Watch may be extended.

Strong Wind Watch

Area: Canterbury High Country

Period: 24hrs from noon Tue, 9 Apr - noon Wed, 10 Apr

Forecast: Northwest winds may approach severe gale in exposed places.

Area: Fiordland

Period: 22hrs from 8pm Mon, 8 Apr - 6pm Tue, 9 Apr

Forecast: North to northwest winds may approach severe gale in exposed places.

Issued: 8:43pm Mon, 8 Apr
Next update: 10am Tue, 9 Apr

[Storm Struck]

Yesterday was certainly quite warm and I'm sure today will be too if we get a few hours of sunshine once the high cloud breaks.
Last night must be fairly close to an overnight sustained warm temperature for April.
Hovering between 20C and 22C, only briefly dropped to 18C at 7am now back to 23C.
More overnight lows you would expect to see in January.

I'd imagine the red warnings will come out today for the west coast and Southland. Certainly quite abit of significant rain coming.
The effects on NSW and QLD are evident on how moisture laden the atmospheric river is.
It's still fluctuating in terms of rain for the plains and coast, maybe latest between 40-50mm.

[Razor]

Looking at the West Coast Regional Council stations, several of the mountainous sites have already pushed into the 300-400mm range, and the event only half done. Interesting day ahead, especially with the next intense wave later today into tomorrow.

Personally I think this warrants a red warning now, I'd be particularly concerned about the Franz Josef area and the Waiho River especially

[darcyplumb]

I really don’t like the way the red warnings are implemented. Perhaps someone with more info can explain it to me. The issue I have is that MS can state days in advance that they think an event will warrant a red warning being issued but they only issue the actual warning within hours of the event starting - or in this case - during the event. They did the same last year with the red wind warning for Canterbury.

[Razor]

I really don’t like the way the red warnings are implemented. Perhaps someone with more info can explain it to me. The issue I have is that MS can state days in advance that they think an event will warrant a red warning being issued but they only issue the actual warning within hours of the event starting - or in this case - during the event. They did the same last year with the red wind warning for Canterbury.

Red warnings are issued in consultation with local authorities as I understand it. Councils/ Civil defence/ emergency services etc

[wembley]

Down south there is to be rain to some degree in the south tomorrow, then showers for Friday and better for Saturday. At least if Newshub are to be believed.

[darcyplumb]

I really don’t like the way the red warnings are implemented. Perhaps someone with more info can explain it to me. The issue I have is that MS can state days in advance that they think an event will warrant a red warning being issued but they only issue the actual warning within hours of the event starting - or in this case - during the event. They did the same last year with the red wind warning for Canterbury.

Red warnings are issued in consultation with local authorities as I understand it. Councils/ Civil defence/ emergency services etc

Thanks Razor. I knew they liaised with relevant authorities but i don’t understand why they wait to issue the warning. If they think it needs a red, why not get the warning out sooner rather than later?

[Storm Struck]

Unsure of the April maximum Christchurch temperature record I'd imagine around 30C or 31C?
Currently 28.2c and still climbing.

[darcyplumb]

Unsure of the April maximum Christchurch temperature record I'd imagine around 30C or 31C?
Currently 28.2c and still climbing.

Geez you’re lucky. We are stuck under the miserable NW cloud. It’s mild, around 22 degrees. It’s actually so dull that I almost need the interior lights on.

[Bradley]

Unsure of the April maximum Christchurch temperature record I'd imagine around 30C or 31C?
Currently 28.2c and still climbing.

The April record for Chch airport is 29.9C in 1978

[Razor]

Unsure of the April maximum Christchurch temperature record I'd imagine around 30C or 31C?
Currently 28.2c and still climbing.

Heavier cloud cover now, I expect we have peaked

[Storm Struck]

Yeah got to 28.4C and then the high cloud returned. Would have easily been close to that temperature if the sun stayed out.
Lighter N-NE has turned moderate NW though so more air movement now, still 27C under this arch.

[Storm Struck]

Certainly surprises me that they havnt forewarned the situation, given the outcomes on better warning systems during the Auckland floods and Cyclone Gabrielle.
As I'm aware the preparedness and local information is meant to be prioritised across to the general public with as much information as possible including the monitoring of current river levels and breaches etc.
Perhaps in this case have a focus on the slice of west coast that has already received the bulk of the rainfall since 6am yesterday, and therefore begin with the Red warning for this area.

[Razor]

Heavy spillover shower in Halswell right now. 23 degrees at 7:50pm

[Bradley]

Practically no rain whatsoever overnight in Lake Brunner, seems to be a more southern event

[tornado]

I really don’t like the way the red warnings are implemented. Perhaps someone with more info can explain it to me. The issue I have is that MS can state days in advance that they think an event will warrant a red warning being issued but they only issue the actual warning within hours of the event starting - or in this case - during the event. They did the same last year with the red wind warning for Canterbury.

and in auckland 27 january last year. they did it when the damage was already done. shocking .

[Razor]

Practically no rain whatsoever overnight in Lake Brunner, seems to be a more southern event

Was always forecast to be a Westland focus, not Grey District so much

Some upper catchment gauges have now recorded 700mm plus for the event

Waiho and Hokitika Rivers have breached their alert levels, much more rain to come.

[Orion]

The overcast aloft here must be very thick, I would need lights on indoors to read comfortably.

Rain has just started splattering the north-facing windows.

24.2°C now, low was around 19°C early in the morning.

[Razor]

Good heavy rain here in Chch. So welcome

[Richard]

Managed to receive 13mm overnight

[Storm Struck]

A good splash for you there Richard although much more needed for sure.
The rain was quite heavy last night for about an hour and a half, has been on and off since but more drizzly this morning.
Around 15-18mm fell overnight mainly during the heavy spell.
It will be fairly patchy today and clear off this evening before returning again tomorrow with scattered showers across the region.
The top of the south has seen much needed rainfall including eastern Marlborough, and some coastal roads closed due to wild weather and king tides.

[Nev]

Below is West Coast Council's Westland 7 day rainfalls (running north to south) to 9am this morning (Apr 14), with most of that rain falling in the 3 days from Apr 09 to 11.