Are We Heading Into An El Niño?
As the La Niña signal continued to fade throughout the Pacific Ocean during February/March, most of the country (apart from the north) has noticed a drying out of sorts. Soil moisture levels are on the decrease and we saw late season heat arriving from the interior, making for a hot March.
Victoria offered a few moments of brilliance as the East Coast became quieter. It’s only in the last couple of weeks that we’ve seen moisture return to the east as the southern states go through a bit of a lean patch.
The question on everyone's lips is will we be rebounding from a triple La Niña back into El Niño? And what does this mean for surf?
In short a rebound El Niño event looks almost certain, but seasonal forecasts at this time of year for the next spring/summer are at their least accurate. This is thanks to something called the “Spring Predictability Barrier”. Spring being our autumn as it's an American term.
The barrier in predictability at this time of the year is due to the atmosphere and ocean decoupling with the weakening of sea surface temperature differences across the Pacific Ocean (whether that be La Niña or El Niño). At this time there is a lot of noise if the statistical model forecasts which only becomes clearer once heading into our winter.
Dynamical models do a slightly better job by taking in the most recent available data like sub-surface temperature profiles while also updating more regularly.
The chart left shows the predictability of dynamical models compared to statistical models at this time of year, and you can see while still below 40% during March the dynamic models are of much greater use than statistical.
Taking the unpredictability into account, most dynamic models are showing a developing El Niño through our winter/spring and into next summer. It’s also expected to be quite a significant El Niño event as well, with the warming throughout the Pacific pushing it into the strong threshold.
Keeping the unpredictability barrier in mind, here's my reasoning for going with what the current dynamic models are forecasting.
Firstly following three La Niña's in a row, the equatorial Pacific Ocean is in a charged state with a large pool of warmer than normal water sitting in the western Pacific, spreading east just below the surface through the central Pacific and surfacing to the east.
This potential heat energy is primed and ready to be brought to the surface if easterly trade-winds (the mechanism driving cold water upwelling and a La Niña state) become relaxed or give way to westerly wind bursts.
Secondly, we've already seen periods of relaxed easterly trade winds across the equatorial Pacific Ocean as well as westerly wind bursts through February and March. This has allowed warm water to take the place of the cold across the central and eastern Pacific bringing us to the current neutral position. The all important Niño 3.4 region is now sitting at a level 0.0 following three years of being negative.
Having westerly wind bursts so early in the season and an abundance of warm, subsurface water helps prime the Pacific for a big rebound to El Niño. The current tropical activity across the north of Australia looks to be the straw that breaks the camel's back.
This activity is linked to an active phase of the Madden Julian Oscillation pushing east, into the Western Pacific Ocean and this will bring with it another westerly wind burst, helping warm the equatorial Pacific Ocean into May.
Long-range seasonal forecasts have further westerly wind activity in and around the Date Line (180°) throughout May and further into June/July which will help warm the Pacific Ocean.
Pending an anomalous, strong burst of easterly trade-winds it looks like we’ll be in a fully fledged El Niño event come spring time, peaking through summer 23/24.
How this effects the coming surf seasons depends on how quickly we transition from the current state.
The impact of El Niño on the Australian swell climate under isn’t as clear cut as La Niña, but as a guide, we can expect less easterly swell across the East Coast, replaced by an increase in southerly swell energy. The south-eastern states and Tasmania/New Zealand are expected to see more Southern Ocean groundswell, while to the west there should be a reduction in high-riding, mid-latitude storms.
Indonesia should see a return to more reliable, longer-period groundswells after a run of weaker, mid-period energy the last couple of years. The winds depend on how the Indian Ocean Dipole plays out, and at this stage we could be heading towards a weak positive event during spring which would see normal to slightly stronger than normal trades across eastern Indonesia, more variable around Sumatra.
We’ll continue to monitor developments over the coming months and provide a clearer outlook for each region as we become more confident.