La Niña Update

Craig Brokensha picture
Craig Brokensha (Craig)
Swellnet Analysis

TLDR:

  • El Nino peaked late last year.
  • We’re currently in a neutral ENSO state, trending towards La Nina.
  • A tongue of cool water has appeared in the eastern Pacific Ocean, a key signature of a developing La Niña.
  • Sea surface temperature observations in the critical Niño 3.4 monitoring region have dipped below 0°C, with further cooling expected over the coming months as stronger than normal trade-winds persist.
  • La Niña is likely by spring, peaking later in the year.

Climate monitoring is a great lesson in patience.

The major drivers play out on weekly to seasonal timescales, sometimes interacting with each other, and it’s only afterwards that we start to see the downstream effects in the ocean and atmosphere.

This brings us to an update on the current transition in sea surface temperatures across the equatorial Pacific Ocean.

It’d be easy to forget that we recently had an El Niño. Arguably, it was overshadowed by the preceding La Nina ‘three-peat’ and it was also weakened by the weight of warm ocean water surrounding eastern Australia, yet it peaked late last year and has been weakening ever since. We’re now in a neutral phase.

Since El Nino’s peak, we’ve seen a steady release of surface heat across the Pacific Ocean. The catalyst for this was a relaxation of the westerly winds that drive El Niño - and in turn pile up warmer water (and also elevate sea levels) in the eastern Pacific.

Once these winds backed off, the warm, elevated water started to flow back to the west where sea levels were relatively lower. It’s a simple ‘conservation of energy’ situation.

This, in addition to recent bursts of strong easterly trade-winds, caused a pool of cold water to upwell in the eastern Pacific Ocean. This cold pool originated in the western Pacific Ocean late last year, with it making its way east, hidden below the surface during the last six months.

With the strong easterly trades as a driver, a tongue of cold water is now visible across the eastern Pacific Ocean. Not only is this tongue of cold water a downstream effect, as referenced earlier, it’s also the key signature of a developing La Niña event.

If it happens, it’ll be the fourth in five years.

Sea surface temperature anomaly chart for May 28th. Note the upwelling signal in the east. (NOAA)

The above explanation will satisfy most people, however the curious surfer might ask, ‘Well, what’s driving the stronger than normal easterly trade-winds?’

The answer to that - and it also includes the related westerly wind bursts - is the Madden Julian Oscillation, or MJO.

The MJO is the wave of tropical activity that circumnavigates the globe. When the MJO is in an active phase, it produces strong westerly winds within its vicinity (aiding cyclone formation), while at the same time, drawing in strong easterly trade-winds to the east.

This has been the case over the last week or so in the Arabian Sea and Bay of Bengal, thanks to an active MJO stalling in the region..

Surfers currently in the Maldives and Sri Lanka would be well aware of this stalling MJO signal with strong, blustery westerly winds ruining the surf across some breaks. It also spawned Severe Tropical Cyclone Remal in the Bay of Bengal over the weekend.

It’s this instability that’s driving the strong easterly winds over in the Pacific basin, promoting upwelling in the eastern regions.

The teleconnections at play here, spanning tens of thousands of kilometres between the Indian and Pacific Oceans, are astounding in scope. The world shrinks under their influence.

The yin and yang of the MJO (May 19-27). Stronger than normal west winds (red) depict the location of the active MJO, with stronger than normal east winds (purple) feeding in from the Pacific Ocean (NOAA)

It’s also these westerly winds that have likely killed off the positive Indian Ocean Dipole event for the coming season, preventing strong, upwelling south-east winds from developing. Surfers in Indonesia will be thankful for that.

Thanks to this active MJO signal, and the stronger than normal easterly trade-winds feeding into it, sea surface temperature observations in the all important Niño 3.4 monitoring region* have just dipped below the 0°C mark. They’re expected to keep cooling over the coming fortnight with another episode of strong easterly winds on the cards.

If it happens, this should push us further towards La Niña, with a peak due later in the year.

With the slow transition between El Niño to neutral over our autumn, it hasn’t influenced the East Coast’s swell regime as favourably as we’d have hoped, with relentless south swells but no meaningful easterly energy.

As the Pacific Ocean continues to transition through winter, high pressure looks to remain dominant across most of the country, with no clear swell signal in favour of more east energy visible for the East Coast, rather a continuation of southerly swells.

Over to the west, the Indian Ocean looks to provide plenty of mid-latitude storms and this points to westerly swells for South Australia and Victoria, though with favourable winds.

We’ll continue to monitor the cooling in the eastern Pacific Ocean and evolution of the highly likely La Niña over the coming months.

//CRAIG BROKENSHA

*The Nino 3.4 region is an area in the central-eastern Pacific Ocean which best represents the state of ENSO (El Niño/La Niña or neutral). When the average of sea surface temperatures in the region are above a certain threshold, El Niño is declared, and when below a certain threshold, La Niña is declared.

Comments

AlfredWallace's picture
AlfredWallace's picture
AlfredWallace Friday, 31 May 2024 at 6:40pm

Craig. Thanks ever so much for your continuing streams of meteorology and oceanic explanations. It’s incredibly interesting and much appreciated. AW

Sprout's picture
Sprout's picture
Sprout Friday, 31 May 2024 at 7:03pm

So the MJO screwed us out of a dry El Nino (SEQLD), can the reverse happen and we get a drier than normal La Nina? 4 years of rain, ergh. Or do we need a positive VRH to get good weather back?

(Viccos Returning Home)

Craig's picture
Craig's picture
Craig Saturday, 1 Jun 2024 at 2:03am

More so the warmer than normal warm signal surrounding Australia during the El Niño provided the moisture input. Amplified by passes of the MJO.

Remember not all El Niño's are dry for Australia with La Niña's having a greater influence to our climate bringing wetter than normal conditions.

And re your question not really. With the warm water associated with La Niña's they are wetter regardless of the passing MJO signal even if suppressed for a short period.

Sprout's picture
Sprout's picture
Sprout Saturday, 1 Jun 2024 at 6:55am

Legend, thanks Craig!

Charlie Chalk's picture
Charlie Chalk's picture
Charlie Chalk Saturday, 1 Jun 2024 at 12:18pm

bahaha VRH.. problem is there is a positive feedback loop:
la nina -> flat southern ocean -> Vicco head north -> negative VRH signal -> further la nina.

Solitude's picture
Solitude's picture
Solitude Saturday, 1 Jun 2024 at 7:37am

Thanks for teaching Craig. It’s great to keep learning and abreast of the world around us. For me the most mind blowing comment was how events in the Indian have such an effect tens of thousands of km away in the pacific. In awe.

batfink's picture
batfink's picture
batfink Saturday, 1 Jun 2024 at 8:35am

“Sea surface temperature observations in the critical Niño 3.4 monitoring region have dipped below 0°C, with further cooling expected over the coming months as stronger than normal trade-winds persist.”

Craig, thank for this summary. Between you and the ABC weather guy (genius, such a good communicator) I know much more than I reasonably should.

But this sentence above. It’s wrong isn’t it? You seem to be suggesting sub-zero ocean temperatures at the equator. Aren’t you referring to the anomaly, not the actual ocean temp, which is what this says.

Yours humbly, Batfink.

Also, I appreciate the tl:dr, but any bastard who doesn’t have the wit to read this in full is not deserving of the tl:dr. Fark ‘em. :-)

Craig's picture
Craig's picture
Craig Saturday, 1 Jun 2024 at 9:54am

Thanks BF.

Agh yes that's the average sea surface temperature anomalies dipping below zero. Still very warm as it's in the tropics.

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming Saturday, 1 Jun 2024 at 9:00am

Im more confused than ever but all i care about is this.

"but it’s also these westerly winds that have likely killed off the positive Indian Ocean Dipole event for the coming season, preventing strong, upwelling south-east winds from developing. Surfers in Indonesia will be thankful for that."

Back soon and ive been watching the winds and they have been a real good mix and a solid swell hit this week.

Pngy's picture
Pngy's picture
Pngy Saturday, 1 Jun 2024 at 3:29pm

Second this!! Eager to learn more

vicbloke's picture
vicbloke's picture
vicbloke Saturday, 1 Jun 2024 at 9:16am

Thanks Craig. Basically you are saying that surf coast should be ok until later in the year and then we might as well go into hibernation for the spring and summer?

Standingleft's picture
Standingleft's picture
Standingleft Saturday, 1 Jun 2024 at 10:14am

Masterful Craig how you tie this all together.
Where do we nominate you for meteorologist of the year?
Or at least a weather-off showdown against Nate Byrne

bbbird's picture
bbbird's picture
bbbird Saturday, 1 Jun 2024 at 5:14pm

thanks for the great summary Craig
Does the prevailing easterly wind flow mean we can capture some more pacific flotsam?

Wonder how much beach property protection will be done before the next big ECL....

what happens if you just dump rocks onto eroding beaches...

Lanky Dean's picture
Lanky Dean's picture
Lanky Dean Monday, 3 Jun 2024 at 12:11am

Thanks Craig
100 percent.
The more moon cycles , the more seasons
The more I observe.

tiff's picture
tiff's picture
tiff Monday, 3 Jun 2024 at 1:22pm

'Over to the west, the Indian Ocean looks to provide plenty of mid-latitude storms and this points to westerly swells for South Australia and Victoria, though with favourable winds.'

Finally!

Swany's picture
Swany's picture
Swany Monday, 10 Jun 2024 at 6:47pm

Reports from mates living in Bali are that the wetsuits are back on….