Mid August West Coast/ Nelson/ North Island flooding & record warmth

[Razor]

Thought I'd start a new thread for the upcoming event which Metservice is already attributing the colour Orange too. Models have consistently gone big in the coming week for Nelson and the West Coast in particular, but it also looks like the North and west of the North Island is going to cop it.

A good old " atmospheric river " again

From MS

Severe Weather Warnings
Extended period of heavy rain for the northwest of the South Island

A complex trough of low pressure, preceded by a moist northerly flow, is expected to move onto New Zealand from the Tasman Sea from Monday night to Tuesday, stay slow-moving on Wednesday, then move eastwards across the South Island during Thursday. This weather system is forecast to bring an extended period of northerly rain to northern and western parts of the South Island, where Heavy Rain Warnings and Watches are now in force.

This is likely to be a significant event, especially for places where soils are already saturated from recent rain. People are advised to keep up to date with the latest forecasts, as some areas could be upgraded to a Red Warning, and more areas will be added.

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: The Tasman District west of Motueka

Period: 54hrs from 3am Tue, 16 Aug - 9am Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 350 to 550 mm of rain to accumulate about the ranges, and lesser amounts about low lying areas. Peak rates of 10 to 20 mm/h about the ranges, especially from Tuesday evening. Note, heavy rain is likely to continue through to Thursday evening, and the warning will probably be extended.

Area: Buller

Period: 54hrs from 3am Tue, 16 Aug - 9am Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 300 to 500 mm of rain to accumulate about the ranges, and lesser amounts about the coast. Peak rates of 10 to 20 mm/h about the ranges, especially from Tuesday night. Note, heavy rain is likely to continue through to Thursday evening, and the warning will probably be extended.

Area: Westland

Period: 39hrs from midnight Mon, 15 Aug - 3pm Wed, 17 Aug

Forecast: Periods of heavy rain. Expect 250 to 400 mm of rain to accumulate about the ranges, and lesser amounts about the coast. Peak rates of 10 to 20 mm/h about the ranges. Note, heavy rain may continue through to Thursday, and the warning will probably be extended.

Heavy Rain Watch

Area: The Marlborough Sounds and Richmond Range, including the Rai Valley

Period: 51hrs from 6am Tue, 16 Aug - 9am Thu, 18 Aug

Forecast: Periods of heavy rain. Rainfall amounts may exceed warning criteria. Note, heavy rain is likely to continue through to Thursday evening, and the watch will probably be extended.

Area: The Tasman District from Motueka eastwards, also Nelson

Period: 52hrs from 5am Tue, 16 Aug - 9am Thu, 18 Aug

Forecast: Periods of heavy rain. Rainfall amounts may exceed warning criteria. Note, heavy rain is likely to continue through to Thursday evening, and the watch will probably be extended.

Issued: 9:33am Sun, 14 Aug
Next update: 9pm Sun, 14 Aug

[NZ Thunderstorm Soc]

Hopefully we will miss out of this one this time. Sadly looks like Buller/NW Nelson plus western areas of the North Island may cop it again.

[spwill]

Current modelling has the rain event mainly focused on the Nelson/West Coast region.

Thursday is looking like the rain day for us in Auckland, not expecting any issues here. See what the modelling does next couple of days.

[Bradley]

I've never seen a warning put out by Metservice mentioning 700mmm-800mm of rain over a 48 hour period before - absolutely incredible

[Razor]

Yes, pretty stark warnings. Fact of the matter is this event looks to be way more than 48 hours too

From MS:

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: Mount Taranaki

Period: 36hrs from 6pm Wed, 17 Aug - 6am Fri, 19 Aug

Forecast: Expect 250 to 350 mm of rain to accumulate. Peak rates of 15 to 25 mm/h.

Area: The Tasman District west of Motueka

Period: 61hrs from 5am Tue, 16 Aug - 6pm Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 400 to 650 mm of rain to accumulate about the ranges, and 150 to 250 mm about low lying areas. Some models indicate 700 to 800 mm about the ranges during this period. Peak rates of 10 to 15 mm/h about the ranges on Tuesday, then 15 to 25 mm/h during Wednesday and Thursday.

Area: The Marlborough Sounds, Bryant and Richmond ranges, including the Rai Valley

Period: 56hrs from 1pm Tue, 16 Aug - 9pm Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 300 to 450 mm of rain to accumulate about the ranges, and 150 to 250 mm about the Sounds. Peak rates of 10 to 15 mm/h about the ranges.

Area: Buller

Period: 62hrs from 4am Tue, 16 Aug - 6pm Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 300 to 500 mm of rain to accumulate about the ranges south of Little Wanganui, and 150 to 250 mm elsewhere. Peak rates of 10 to 15 mm/h about the ranges.

Area: Westland

Period: 65hrs from 1am Tue, 16 Aug - 6pm Thu, 18 Aug

Forecast: Periods of heavy rain. Expect 350 to 550 mm of rain to accumulate about the ranges, especially between Bruce Bay and Otira, and 150 to 250 mm about the coast. Peak rates of 10 to 20 mm/h about the ranges.

[JP.]

Surely some areas will get upgraded to a red warning with some of those numbers mentioned. Feel for the west coast as this could bring some of the highest 48 hour totals of the whole year so far.

[Lawrence]

Surely some areas will get upgraded to a red warning with some of those numbers mentioned. Feel for the west coast as this could bring some of the highest 48 hour totals of the whole year so far.

Agreed.We will see what they upgrade it to today.Surely, looking at the numbers the threshold should be passed at some point and lead to a red designation.

[darcyplumb]

Surely some areas will get upgraded to a red warning with some of those numbers mentioned. Feel for the west coast as this could bring some of the highest 48 hour totals of the whole year so far.

Agreed.We will see what they upgrade it to today.Surely, looking at the numbers the threshold should be passed at some point and lead to a red designation.

I believe red warnings are issued after consulting with local council and civil defence which may make things a bit more complicated than your ‘standard’ orange warning.

[harveyt86]

Would be very surprised not to see a red warning this morning. Especially with what they have had to deal with around those parts from recent flood events.

Edit: Well I was wrong!

[darcyplumb]

Would be very surprised not to see a red warning this morning. Especially with what they have had to deal with around those parts from recent flood events.

Edit: Well I was wrong!

The very worst of it seems to be tomorrow (according to the MS warning) so the red warning may come tonight.

[Razor]

Been chatting with my mate who is the Civil Defence controller over there today. They are getting an updated MS advice stream about now. Seems the models are looking at a reasonably wide range of 600m m -1200mm by Sunday, so somewhere in the middle of that looks likely. Add the freezing level near the top of Mt Cook so thats a lot of snowmelt plus rain for the catchments. Messy.

[spwill]

A very warm system coming onto NZ but cloud and rain will keep temperatures down but still warm for August. Current weather here is 17C, dew point 14C, high cloud, a fresh NE breeze now.

[Dean.]

A red warning just issued for Buller and Westland

Sent from my SM-A226B using Tapatalk

[darcyplumb]

State of Emergency now declared for the entire West Coast region.

[Nev]

Only got down to 14.8C here overnight.

New Auckland Aero record high Aug Tmin (for the 24 hrs to 9am this morn)...
https://twitter.com/MetService/status/1 ... r_9qQrAAAA

[harveyt86]

Only got down to 14.8C here overnight.

New Auckland Aero record high Aug Tmin (for the 24 hrs to 9am this morn)...
https://twitter.com/MetService/status/1 ... r_9qQrAAAA

Thankfully it's not summer!

[Tornado Tim]

More portions of the North Island now have an Orange Warning.

Of most concern is modelling identifying a wavering pattern with jetstream, the event could turn out to be bit longer if it thats the case and more risk for flooding.

Nearly all of NZ is under cloud, with high amounts of moisture being piped in from the tropics.

image.png

[David]

Not often you see a warning of 110-140mm for Auckland. GFS is being much more conservative with around 60mm

[spwill]

Thursday night/ Friday morning has very warm humid air across the North Island and upper South Island, perhaps some new minimum temperature records? There is the cooling affect of the rain.

[harveyt86]

Have to think the Waikato River will be full to the brim after this with such widespread heavy rain over the entire catchment. Don't have much knowledge of the river system in general but I imagine the hydro lakes do a pretty job on minimising/moderating downstream impacts?

[asuth]

We are in Nelson and it has been raining heavily all morning. Our lawn is a lake and there is already surface flooding around the city. With another 300+mm or rain still to come over the next few days according to many models, I am baffled as to why Nelson/Tasman hasn’t been issued a red warning.

[Tornado Tim]

Have to think the Waikato River will be full to the brim after this with such widespread heavy rain over the entire catchment. Don't have much knowledge of the river system in general but I imagine the hydro lakes do a pretty job on minimising/moderating downstream impacts?

We have had fairly high river flow the last few weeks with the side banks being full and some small trees underwater.

I think Murcury Energy was expecting this as Lake Taupo has been steadily being drained since mid late July.

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[harveyt86]

Thanks Tim. Hopefully they have everything in order for controlled releases once the rain stops and the lower catchment has some time to drain! Must be an interesting job in times like this.

[Richard]

This air mass is certainly bringing some warmth with it, just on 20deg, be a warm night coming up too.

[Nev]

Currently 22.7C at Culverden according to MS...