Forecaster Blog: La Niña conditions are here, what does it mean for Surf?

24 Sep 2020 8 Share

Ben Macartney

Chief Surf Forecaster

You might already be onto the fact that were now entering the early stages of a La Niña event – and as long as you dont mind a bit of wet weather, thats usually a good thing when it comes to surf over the coming months. While a La Niña hasnt officially been declared (the BOM is still on “La Niña Alert”), many of the key tropical Pacific Ocean indicators are continuing to slide towards a full blown, borderline moderate La Niña event. Those indicators include:

  • Below average sea surface temperatures (SSTs) and sub-surface temperatures across the central and eastern tropical Pacific.
  • Above average SSTs over the tropical western Pacific Ocean.
  • Changes in the atmospheric circulation pattern, including above average tradewinds at the surface.

The signature of a La Nina: Cool SST anomalies over the tropical central-eastern Pacific and warm SST anomalies across the tropical western Pacific. Source: BOM.

The signature of a La Nina: Cool SST anomalies over the tropical central-eastern Pacific and warm SST anomalies across the tropical western Pacific. Source: BOM.

But just what does that mean for surf potential in the rest of 2020 and early 2021? Thats the question Ive been looking at over the past few weeks – and to be honest, theres no simple answer. However, scroll a bit further down and youll find an analysis of spring surfing conditions during previous La Niña years, specifically looking at the 2007/08 and 2010/11 events.

El Niño Southern Oscillation (ENSO) and the Walker Circulation
First lets take a couple of steps back and look at exactly what ENSO describes. ENSO is a natural atmospheric cycle encompassing the tropical Pacific Ocean. It describes a process known as Walker Circulation, whereby tropical heat is moved via easterly trade-winds, transporting warm water and air from east to west. That warm, moist air eventually rises over northern Australia and the Coral Sea, condensing to form clouds, precipitation and general storminess during the Southern Hemisphere summer. Now drier and cooler, the air is then transported back east at high altitudes, where it sinks back down over the eastern Pacific Ocean.

ENSO in its neutral state. Source: NOAA.

ENSO in its neutral state. Source: NOAA.

La Niña: The supercharged version of the ENSO cycle. La Niña occurs when easterly tradewinds are stronger than average. This has the dual effects of causing warm, tropical water to pool over the western Pacific Ocean (including the Coral Sea) while causing cooler than average SSTs in the central and eastern tropical Pacific. These mechanisms create a feedback loop, effectively sending the Walker Circulation into overdrive.

The above average SSTs over the western Pacific Ocean can result in an earlier onset of the monsoon and a higher incidence of tropical lows, troughs, and tropical cyclones in the Australian region throughout the season. That can also spill over to above average easterly swell activity over the Tasman Sea.

La Nina conditions: The Walker circulation goes into overdrive. Source: NOAA.

La Nina conditions: The Walker circulation goes into overdrive. Source: NOAA.

ENSO is only One of the Big Drivers of Australian Climate
Of course, its really not that cut and dried. ENSO and the impending La Niña are just one driver of Australias weather and surf-potential. Theres also the Indian Ocean Dipole (IOD) and the the Southern Annular Mode.

Weakly Negative IOD: The IOD is basically the Indian Oceans version of ENSO. Positive and negative phases of the IOD also fluctuate with shifts in the SST profile across the tropical Indian Ocean. A majority of climate models predict a weakly negative IOD throughout October, before it returns to neutral in November.

A negative IOD often goes hand in hand with a La Nina. This year it's looking weakly negative to neutral. Source: BOM.

A negative IOD often goes hand in hand with a La Nina. This year it's looking weakly negative to neutral. Source: BOM.

Many particularly strong La Niña events, go hand in hand with a negative IOD. Thats characterised by warmer than average SSTs pooling over the tropical Indian Ocean, around Indonesia and near Australia. That also enhances convection over the tropical north-west, contributing to above average rainfall and also a higher incidence of low pressure moving west to east across the mainland – in theory flowing through to a higher incidence of easterly swell sources for the East Coast.

A negative IOD can bring plenty of weather across the mainland, enhancing rainfall - and eventually swell-potential for the East Coast. Source: BOM.

A negative IOD can bring plenty of weather across the mainland, enhancing rainfall - and eventually swell-potential for the East Coast. Source: BOM.

Past La Niña Years: 2007/08 and 2010/11
The crux of it is that no two seasons are the same. Each year we see a unique set of atmospheric drivers producing a unique surf season. But we can look at what the surf was like during previous La Niña events just to get an inkling of what we might see in the way of swell over the coming months.

The last strong La Niña event was a decade ago, when the SOI fell well below zero, peaking at -1.7 during the Spring/ Summer of 2010. Prior to that, there was a moderate event back in 2007/08. You might recall that the transition towards La Niña during the 2007 winter saw a cluster of ECLs, producing a good to epic run of large surf, drawing parallels with the spectacular procession of Tasman lows that left us reeling over the 2020 winter.

Remember this? Throughout history, big swings in ENSO are linked clusters of major swell events across the East Coast. Photo: Phillip Morris.

Remember this? Throughout history, big swings in ENSO are linked clusters of major swell events across the East Coast. Photo: Phillip Morris.

Spring in previous La Niña events: So lets take a look at MSLP anomalies for the some of the spring months – and how that translated into surf for the region.

The 2010/11 Niña was one of the biggest events on record – and the developing 2020/21 event is unlikely to come close. Nevertheless, it gives us an insight into what we might see as La Niña continues to develop over the coming weeks. October 2010 saw a monster, +7 high pressure anomaly straddling the Tasman Sea and NZ, producing a strong easterly bias in the swell regime throughout the month.

A strong high pressure anomaly over the Tasman Sea saw a predominant easterly bias in the swell regime across the eastern seaboard throughout October 2010. Source: BOM.

A strong high pressure anomaly over the Tasman Sea saw a predominant easterly bias in the swell regime across the eastern seaboard throughout October 2010. Source: BOM.

Here’s one example of a coastal trough interacting with the subtropical ridge, setting up an extended run of east swell for the region through early to mid October. Source: BOM.

Here’s one example of a coastal trough interacting with the subtropical ridge, setting up an extended run of east swell for the region through early to mid October. Source: BOM.

Southern Queensland benefited from a couple of solid east and ESE swells through the first half of the month; the second event showing several days of solid surf in the 4 to 6ft+ range with mostly favourable winds from October 10 to 13.

Coastalwatch’s surf report history illustrates the consistent trend in easterly swell across southern Queensland throughout October.

Coastalwatch’s surf report history illustrates the consistent trend in easterly swell across southern Queensland throughout October.

Sydney and surrounds also benefited from a solid run of easterly swell, peaking at more modest 3-5 foot levels around the 12th and 13th, backed up by a new run of SSE swell on the 17th and 18th.

Although not as big, the southern half of the NSW coast also received its fair share of easterly swell.

Although not as big, the southern half of the NSW coast also received its fair share of easterly swell.

In contrast, the 2007/08 La Niña was a moderate event. Once again, we saw a high pressure anomaly developing over the Tasman Sea throughout spring, that by November was showing uncanny similarity to the 2010 pattern depicted above:

Through October and November ’07 a similarly strong high pressure anomaly developed over the Tasman Sea. Source: BOM.

Through October and November ’07 a similarly strong high pressure anomaly developed over the Tasman Sea. Source: BOM.

Most of October saw small to mid-sized south swell across the NSW coast, but that all changed as the high pressure anomaly strengthened towards the end of the month:

An extended run of small to mid-sized ENE swell followed the development of a high and coastal trough over the eastern interior into the end of October 2007. Source: BOM.

An extended run of small to mid-sized ENE swell followed the development of a high and coastal trough over the eastern interior into the end of October 2007. Source: BOM.

Across Sydney and surrounds, most of October 2007 featured a consistent run of south swell, capped off with several days of fun-sized ENE swell into the end of the month.

October 2007 was nothing to write home about across Sydney, but there was no shortage of surf from the south - and later in the month from the east.

October 2007 was nothing to write home about across Sydney, but there was no shortage of surf from the south - and later in the month from the east.

There was no shortage of easterly swell across southern Queensland, but it was mostly small scale stuff, ranging from 1-3 feet for most of November.


There was plenty of east swell across southern QLD throughout November 2007, but size wise, it was pretty modest.

There was plenty of east swell across southern QLD throughout November 2007, but size wise, it was pretty modest.

Stay tuned for a follow up on surf potential for the 2020/21 summer as the La Nina event continues to develop. 

Tags: Forecaster Blog , Ben Macartney , La Nina , topnews (create Alert from these tags)

blog comments powered by Disqus
More From Latest Features
Nick Carroll: Maurice Cole and the Surf Coast Showdown

Nick Carroll: Maurice Cole and the Surf Coast Showdown

The Australian Surfing Icon Is Contesting the Torquay Council Elections This Weekend

1 27 Oct 2020
The Story of How Surfing Almost Lost Mundaka, Then Didn't

The Story of How Surfing Almost Lost Mundaka, Then Didn't

First Sessions: How the Spanish Rivermouth Almost Suffered a Man-Made Death

1 26 Oct 2020
Recent

Nick Carroll: Maurice Cole and the Surf Coast Showdown

The Australian Surfing Icon Is Contesting the Torquay Council Elections This Weekend

1 27 Oct 2020
We're Hiring: Camera Operations Technician

We're Hiring: Camera Operations Technician

27 Oct 2020
Watch: Episode 11 of RIVALS – Mick, Parko and Dingo Face-Off In Pumping Snapper Superheat!

Watch: Episode 11 of RIVALS – Mick, Parko and Dingo Face-Off In Pumping Snapper Superheat!

1 24 Oct 2020
Remembering Biggest Wednesday, Pumping Empty Cokes, and Can You Go Finless at Teahupo'o?

Remembering Biggest Wednesday, Pumping Empty Cokes, and Can You Go Finless at Teahupo'o?

22 Oct 2020
Brazil's Beachies Look Fun as Hell and Gabriel Medina Is Making the Most of Them

Brazil's Beachies Look Fun as Hell and Gabriel Medina Is Making the Most of Them

1 22 Oct 2020
Latest News

Nick Carroll: Maurice Cole and the Surf Coast Showdown

The Australian Surfing Icon Is Contesting the Torquay Council Elections This Weekend

Remembering Biggest Wednesday, Pumping Empty Cokes, and Can You Go Finless at Teahupo'o?

This Week In Surfing: Ten Things from Surfing & the Internet on the Week That Was October 23 2020

Popular This Week

Remembering Biggest Wednesday, Pumping Empty Cokes, and Can You Go Finless at Teahupo'o?

This Week In Surfing: Ten Things from Surfing & the Internet on the Week That Was October 23 2020

Video: The Fizzlot kids – SW Grom Bash

A stoked out portrait of Australian Junior Surfing in the year 2018.

Go to Top