Are we heading for a double-dip La Niña?

Craig Brokensha picture
Craig Brokensha (Craig)
Swellnet Analysis

TL;DR

  • El Niño events generally return to neutral the following year, unlike La Niña which has a 50% of returning back to La Niña
  • This is called a double-dip La Niña
  • A recent burst of west-flowing surface currents may be the catalyst for a double-dip La Niña
  • The prediction is bolstered by a developing negative Indian Ocean Dipole event - which usually coincides with La Niña
  • La Niña brings moisture to Australia, plus increased swell for the East Coast but a decrease in the southern states

The chances of back to back La Niña events (know as a double-dip La Niña) into the 2021/22 summer have just increased slightly.

This is great news for East Coast surfers though not what Victorian and South Australian surfers want to hear, especially with the last event being so fresh in their memories.

Before we get stuck in, it's worth noting that El Niño and La Niña don't swing back and forth like a pendulum, and that there's even a neutral phase between the two.

Historically, once a La Niña event has run its course the chances of back to back La Niña events is 50%, yet the same isn't true for El Niño. The reasoning behind this is explained in more detail below, but as we move through winter we're starting to see a few signals which are favouring a double-dip Niña event.

El Niño and La Niña events aren't symmetrical. Meaning they don't mirror each other from one side of the Pacific Ocean to the other.

We know that during La Niña events, warm water piles up in the western Pacific Ocean, bringing increased convection and moisture to the Australian region, with cooler waters upwelled to the east. El Niño is the opposite with warm water to the east, and cooler towards us in the western Pacific Ocean, leading to subdued convection and less moisture for our region.

Where the peak of this cool/warm (La Niña/El Niño) water anomaly sits across the Pacific varies between the two phases, and this is where the symmetry falls apart. La Niña's see the cold pool developing further west than where the warmer El Niño pool sits, which is further east (shown below). If all were equal we'd see the same region of ocean cycling between cold/warm events but they're slightly offset.

Also El Niño's are generally stronger regarding the shift in surface temperature from normal. That being the warm water anomaly for the ten strongest El Niño's is larger than the cool water anomaly.

The asymmetry between El Niño/La Niña events. Peak in temperature is in a different region, and El Niño's are stronger

So if the shift in sea surface temperature is larger for El Niño, then why don't we see back to back El Niño events compared to the relatively weaker La Niña signal?

The answer is in the strength of the feedback loop. During warmer water El Niño events, heat is released into the upper atmosphere and flows back to the poles. This feedback system is much greater than La Niña's helping it reset to neutral more quickly. La Niña's instead see a slower return to neutral and this in turn slightly primes the ocean and atmosphere for another La Niña event to kick back in the following year.

This phenomena is shown in the graph below which plots the change in sea surface temperatures across the Niño 3.4 sector (central) equatorial Pacific Ocean.

Every first year El Niño/La Niña is plotted from 1950 (left), with the following year's developments to the right.

Sea surface temperature anomalies for the Niño 3.4 region for all first year El Niño events (top) and La Niña events (bottom) and the following year. The statistical significant double-dip La Niña can be clearly seen

What these statistics show us is that during the year following an El Niño, conditions, on average, return to neutral and sea surface temperatures back to normal.

However, following first year La Niña events, conditions have a tendency to stay on the La Niña side, though on average not as intense as the previous year's event. This is known as a double-dip La Niña and statistically it's a 50% chance following the first year of La Niña.

Knowing this, we've been keenly observing events in the central Pacific Ocean regarding any sign of a double-dip La Niña, and in the past fortnight we've seen a few indications that increase the chance slightly above 50%.

Firstly, Kathleen Dohan from Earth and Space Research has done amazing work correlating surface current changes across the equatorial Pacific to the evolution of a La Niño/Niña event.

After filtering out seasonal differences, a clear signal appears which shows that following a westward surface current anomaly (flowing to the west and shown when the blue line dips negative) we see a shift in the Sea Surface Temperature (SST) anomaly the opposite way shortly after. This shift is positive (red line going positive). La Niña events are shown when the red SST line pushes above 1 standard deviation and El Niño events when it dips below -1.

This correlation plays out beautifully and you can clearly see last year's La Niña develop after the surface current dipped towards 2 standard deviations and the SST accordingly rose above 1 standard deviation.

First EOF modes of sea surface current anomaly (blue - positive = easward current) plotted and sea suface temperature anomlay (red). Source: Earth & Space Research

Looking at the past two decades, the strong 1997/98 El Niño clearly stands out, as well as 2010-12 La Niña and 2015/16 El Niño.

First EOF modes of sea surface current anomaly (blue - positive = easward current) plotted and sea suface temperature anomlay (red). Source: Earth & Space Research

This analysis gives us a slight heads up on a possible developing El Niño/La Niña event by monitoring the surface current changes from normal.

So coming back to recent observations, we can see SST (red line) is still returning slowly to neutral following last summers La Niña but with the recent westward surface current anomaly (negative dip in blue line) we can expect those surface temperatures to head back north over the coming weeks, towards La Niña thresholds.

This appears to further increase the chances for a double-dip La Niña. We also have a developing negative Indian Ocean Dipole event in the Indian Ocean (warm water off Indonesia, cooler towards Africa) and this usually goes hand in hand with La Niña.

As for swell, another La Niña would see a summer and autumn similar to the one just gone. It's a plus for those on the East Coast with an increase in swell energy from the east along with winds from the south-east to east, while a shift in the storm track further south brings less swell to the southern states and unfavourable south to south-east winds.

NOAA's Climate Prediction Centre has the chance of La Niña reforming at just over 50% this November/December/January in its latest update so we'll continue to keep a close eye on the developments throughout the Pacific Ocean over the coming months.

Comments

Blowin's picture
Blowin's picture
Blowin Friday, 25 Jun 2021 at 10:15am

FFS Craig. I just went and bought some cool water wax. Lift your game!

Yes, that is an attempt at humour.

juegasiempre's picture
juegasiempre's picture
juegasiempre Friday, 25 Jun 2021 at 10:20am

Surfing aside, I'm glad I'm selling my house because it was far too wet for me this year. Crazy amounts of rain like I've never seen and I thought it might be a few more years of drought until we have another onslaught like this 2020/2021. Mother Nature is pissed and she's just warming up (pun not intended)!

Sprout's picture
Sprout's picture
Sprout Friday, 25 Jun 2021 at 10:40am

Blergh, add another 6 months onto my deck getting done.

davetherave's picture
davetherave's picture
davetherave Friday, 25 Jun 2021 at 10:58am

Fantastic work Craig. Thanks for sharing your very impressive knowledge. A bit of a modern day prophet, ha. This is why I am a Swellnet subscriber.

tango's picture
tango's picture
tango Friday, 25 Jun 2021 at 12:30pm

Great article, Craig.

Poor fellow, my southern coastline.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno Friday, 25 Jun 2021 at 12:55pm

Go East
There's waves in LaNina time,
Go East
Away from onshore slime,
Go East
Except maybe not to Sydney,
Go East
In LaNina where I'd rather be!

tango's picture
tango's picture
tango Friday, 25 Jun 2021 at 3:13pm

Sounds like you started lunch nice and early, VJ.....

Bob Sacamano's picture
Bob Sacamano's picture
Bob Sacamano Friday, 25 Jun 2021 at 2:43pm

I wont say no to another bout of La Nina. Nothing worse than a summer of relentless devil winds.

SDW's picture
SDW's picture
SDW Friday, 25 Jun 2021 at 3:58pm

Very interesting. Another La Nina summer would be extremely helpful after the extreme heat and drought eastern Australia endured for several years up until about 15 months ago.

greyhound's picture
greyhound's picture
greyhound Friday, 25 Jun 2021 at 6:11pm

Can I have my donation back farmers?
Or have the mice eaten it?

Jamyardy's picture
Jamyardy's picture
Jamyardy Friday, 25 Jun 2021 at 6:11pm

Great article Craig, cheers.

I always thought a La Nina followed an El Nino but that appears not to be the case. Looking at the average sea temp anomaly for 3.4 region graphs above, it looks like El Nino Vs La Nina temp anomaly is about the same for each, but for the ten strongest its not, well it also looks like there is only about 10 La Nina in that graph vs maybe 20 El Nino's, with a ~50% double dip rate you would probably expect to see more la Nina's recorded, but maybe I am interpreting the graphs incorrectly.
Craig wrote :
"Also El Niño's are generally stronger regarding the shift in surface temperature from normal. That being the warm water anomaly for the ten strongest El Niño's is larger than the cool water anomaly."

Craig's picture
Craig's picture
Craig Friday, 25 Jun 2021 at 6:36pm

Thanks guys,

JY, regarding the first point, the top ten strongest El Niño's are between 2.25 and 2.75 degrees C above normal, while the top ten La Niña's are only up to 2.25 degrees C below normal.

The second graph shows all first year events, weak to strong from 1950, and as El Niño's are more common than La Niña's that's why there are more lines/events shown for El Niño's compared to La Niña's.

groundswell's picture
groundswell's picture
groundswell Friday, 25 Jun 2021 at 8:31pm

Quote Craig- "As for swell, another La Niña would see a summer and autumn similar to the one just gone. It's a plus for those on the East Coast with an increase in swell energy from the east along with winds from the south-east to east, while a shift in the storm track further south brings less swell to the southern states and unfavourable south to south-east winds."

So NW Australia and mid west Australia will see another rarely surfable summer?
Even the magnets didnt get much swell untill about march even then small.
Waters still warm here but at the moment morning temps (air) have been around 2' - 6'C Too cold for me thanks.
Jeez it must be cold in the desert with these cold easterlies.

Craig's picture
Craig's picture
Craig Friday, 25 Jun 2021 at 8:38pm

Yeah would expect similar if it develops but we'll see how things play out.

groundswell's picture
groundswell's picture
groundswell Friday, 25 Jun 2021 at 9:45pm

thanks Craig..will have to start fishing then.

Island Bay's picture
Island Bay's picture
Island Bay Friday, 25 Jun 2021 at 6:39pm

"The chances of back to back La Niña events (know as a double-dip La Niña) into the 2021/22 summer have just increased slightly."

I remain somewhat sceptical and reckon "slightly" is the operative word.

Great article, though. Cheers, Craig!

nasigoreng's picture
nasigoreng's picture
nasigoreng Friday, 25 Jun 2021 at 7:28pm

"not what Victorian and South Australian surfers want to hear, especially with the last event being so fresh in their memories."

........and Covid life. Hopefully not.

Thanks Craig, great writing and forecasting.

Thegrowingtrend.com's picture
Thegrowingtrend.com's picture
Thegrowingtrend.com Saturday, 26 Jun 2021 at 7:47am

My arms are cooked after last summer/autumn.

Yendor's picture
Yendor's picture
Yendor Saturday, 26 Jun 2021 at 12:56pm

Thanks for this article Craig,

Great info as usual although these types of analysis do make my head hurt a little. Part of me wants to just skim it and get the takeaway while the pedantic part makes me delve into the details and understand what's going on. So thanks I think.

Living in Wellington NZ El Nino/lLa Nina seems to have a pretty ambivalent impact on our surf prospects, it seems to depend a lot on the unique characteristics of each event.

Really strong El Nino has at times had a diabolical impact on our south swells with just too much of a westerly driver, but not always.

mattlock's picture
mattlock's picture
mattlock Saturday, 26 Jun 2021 at 1:01pm

Good article Craig.
Bring back the drought I say.

sean killen's picture
sean killen's picture
sean killen Sunday, 27 Jun 2021 at 7:07am

Great read Craig.. thanks again, hopefully it plays out that way, not just for the waves but the farmering industry etc .. cheers

Aaaandy's picture
Aaaandy's picture
Aaaandy Sunday, 27 Jun 2021 at 12:23pm

Looks like the beer gut is gonna get bigger.

joshea78's picture
joshea78's picture
joshea78 Sunday, 27 Jun 2021 at 3:05pm

F#$K OFF La Nina!

Craig's picture
Craig's picture
Craig Sunday, 11 Jul 2021 at 9:10pm

NOAA have just issued a La Niña watch.. https://www.climate.gov/news-features/blogs/enso/july-2021-enso-update-la-ni%C3%B1a-watch

"As things stand with the El Niño-Southern Oscillation (ENSO), neutral conditions are currently present in the tropical Pacific and favored to last through the North American summer and into the fall. But forecasters at NOAA’s Climate Prediction Center have issued a La Niña Watch, which means they see La Niña likely emerging (~55%) during the September-November period and lasting through winter."

anthony.olsen's picture
anthony.olsen's picture
anthony.olsen Monday, 12 Jul 2021 at 3:48pm

So maybe my shoulder surgery will be full healed once it lifts.

Craig's picture
Craig's picture
Craig Thursday, 15 Jul 2021 at 3:52pm

We're seeing more consensus between global climate models and government agencies regarding the increasing likelihood of a double-dip Niña event, and the latest data from Earth and Space Research also consolidates this. https://www.esr.org/data-products/monthly-enso-index/

We've had a further negative dip in the surface current anomalies (blue line), ie westward flowing surface currents from bursts of easterly trade-winds.

We then look to the red line (sea surface temperature anomalies) to jump back up in response and there's a tiny inflection on the graph here. Watch this space over the next few weeks.

Craig's picture
Craig's picture
Craig Tuesday, 20 Jul 2021 at 9:54am

We're seeing sub-surface (below surface) cool water temperature anomalies strengthening and nearing the surface over in the eastern Pacific Ocean. This will help feed any developing La Niña and won't take much of an easterly burst to upwell to the surface.

This is a cross section of the equatorial Pacific Ocean showing the water column from surface down to 450m depth..

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno Tuesday, 20 Jul 2021 at 9:58am

oh facepalm

Craig's picture
Craig's picture
Craig Tuesday, 20 Jul 2021 at 1:49pm

And here we go, that purple blob forecast from the 24-26th July is easterly wind anomalies over the eastern Pacific. Negative in value as we're looking at zonal (westerly winds) here, so + equates to an increase in the westerlies, while - equates to easterly winds.

Could be the final catalyst to kick off events..

freeride76's picture
freeride76's picture
freeride76 Wednesday, 21 Jul 2021 at 8:29am

Pretty tidy trade burst in the Nino 3.4 area right now Craig.
I'm starting to come on line to this bullish outlook for a double-dip.

Craig's picture
Craig's picture
Craig Wednesday, 21 Jul 2021 at 9:42am

Welcome aboard the double-dip Niña train Steve!

mick-free's picture
mick-free's picture
mick-free Thursday, 22 Jul 2021 at 3:42pm

The dream continues…..double dip La Nina lockdown

bluediamond's picture
bluediamond's picture
bluediamond Wednesday, 21 Jul 2021 at 9:12am

Great read. Thanks.
BOMs already calling the negative IOD.
https://www.abc.net.au/news/2021-07-20/bom-declares-negative-indian-ocea...
And for what it's worth, it's pissing down here, has been for days, and no end in sight. Can't wait for another summer of howling South Easterlies on the south coast. :(

Distracted's picture
Distracted's picture
Distracted Wednesday, 21 Jul 2021 at 9:17am

Could be an interesting rainfall outlook for the next 12 months as the Indian Ocean is already in a negative IOD condition.
https://www.abc.net.au/news/2021-07-20/bom-declares-negative-indian-ocea...

freeride76's picture
freeride76's picture
freeride76 Wednesday, 21 Jul 2021 at 9:38am

the observations here are of constant cloud bands from the west.

classic neg IOD signal.

Craig's picture
Craig's picture
Craig Wednesday, 21 Jul 2021 at 9:48am

Classic north-west in-feed here (yesterday morning)..

freeride76's picture
freeride76's picture
freeride76 Wednesday, 21 Jul 2021 at 10:18am

yep.

Interesting to listen to the daily Met wrap-up on the ABC rural report and hear the talk about rainfall on the western slopes of the ranges.

while we get the cloud but are in the rain shadow of the prevailing systems.

Craig's picture
Craig's picture
Craig Thursday, 22 Jul 2021 at 3:00pm

Here comes the upwelling.

Looks like we're certainly heading towards another La Niña looking at the evolution of the SST's across the equator over the past month..

The final image zoomed in..

Craig's picture
Craig's picture
Craig Friday, 30 Jul 2021 at 7:10pm

New Zealand's NIWA (National Institute of Water and Atmospheric Research) has just gone into La Niña watch, in line with NOAA. Waiting for the BOM over the coming weeks.

southey's picture
southey's picture
southey Friday, 30 Jul 2021 at 8:16pm

I was skeptical after last year did not see the intensity of La Nina i was expecting ( yeah i'm focused on North and West Victorian Precip influence as opposed to Surf ) . Since i saw the breakdown of NW infeeds around July last year the summer didn't matter as much . Obviously the surf influence ( and Qld-NSW coastalfringe Precips were very visual and well documented .

Of interest i think that the Nth Hem influence initiated a ENSO teleconnection to the IOD and out of nowhere this cool subsurface pool looks like its going to supercharge things even more .
Even when NOAA announced a potential La Nina watch i wasn't even focused and was too interested in the IOD .
Funnily enough the recent dry/winter season rains in SE Qld were a tell tale that i was looking more at the Indian as the primary influence . But the Atmosphere is saturated , with water vapour being advected on all fronts .

God help people in low lying areas come storm season . This has the potential to outstrip 2010/2011 .

Usually the standard 18 mth cycle of La Nina is a fair bet . But looking at this now we are looking down the barrel of 54-56 or worst still 73-75 .

This is highly unusual but the SW land division ( SWA ) is usually bone dry during La Nina . Which re interates that the IOD has been triggered by the ENSO and will now bounce back to the East in its influence in Australia as the Negative IOD peaks and then the La Nina starts bearing its teeth come Oct .