La Niña - The End
The first one was a relief; a welcome change from bushfire and drought.
The second set the pattern of easterly swell and rain. It set a few weather records too.
When the third La Niña was announced, however, surfers on the Eastern Seaboard knew they were living through something special. No longer could the old timers brag about the days of yore: these were the glory days.
For almost three full years our easterly swell window has been wide open and active. So much so that even seasonal zones such as the Sunshine Coast fell into one long season of waves. It wasn't always pretty, especially when the Northern Rivers copped the floodwater outflows, but it was extremely active, to the extent that it began to feel normal. No need to rush for this eight foot swell because there'll be another one next week.
But all good things must come to an end, and that end, unfortunately, is here.
The usual starting point of La Niña/El Niño cycles is in spring, with a peak during summer before weakening through the autumn months.
This was the case for our first and second La Niña's, through 20/21 and 21/22, but the trifecta came anomalously early this year, restrengthening through winter and peaking through the middle to end of spring.
La Niña events form under stronger than normal easterly trade-winds blowing across the equatorial Pacific Ocean, creating surface currents which pile up warm water towards the western Pacific (north-east of Australia), while upwelling colder water throughout the central and eastern Pacific Ocean.
Through July we saw a significant easterly wind anomaly along the equator (read: stronger than normal easterly winds), sending us into our third La Niña. The consecutive La Niña's preceding this third also helped bring consecutive negative Indian Ocean Dipole (IOD) events, with the warm water piled up in the western Pacific Ocean, and associated rise in sea levels causing a through flow towards Indonesia.
The end result of the coinciding negative IOD and La Niña events was a significant warm water signal surrounding Australia, from the north-west to north-east leading to significant rainfall, particularly falling inland, this spring.
Meanwhile in Indonesia, anywhere west of Java has seen strong northwest winds spoiling exposed breaks thanks to the negative IOD signal, though this is now breaking down and will continue to into summer.
With the La Niña signal peaking through our spring, we've seen out of season surf and weather impacting the East Coast, with plentiful swells for those with a bit of flexibility in their diary.
At the same time, our southern brethren were rewarded for their patience with multiple days of good surf across the more exposed beaches under a north-easterly flow.
Before we get to ahead of ourselves, the questions have to be asked: Why has the third La Niña signal peaked, and what will prevent it from restrengthening over the coming months?
There are a couple of reasons.
Firstly, the source of cooler water anomalies surfacing throughout the central and eastern Pacific Ocean is starting to shrink while at the same time, the warm water sub-surface signal to the west is showing signs that it's started to transition east in the form of a Kelvin wave (see image below). There has also been a clear warming signal at the surface along the equator in the eastern Pacific over the past week (see image above).
The anomalous easterly trade-winds have also weakened, leading to a weakening of the Walker circulation which drives surface currents and the La Niña signal as whole.
This is in line with most long-range climate models for the Niño 3.4 region, with a fairly steady transition back to a neutral phase due by the end of summer.
It should be noted that any transition from La Niña to neutral or to El Niño isn't like flicking a switch, with an instant change from wet to dry or any other variation. It's a gradual transition as the Pacific slowly warms across equatorial locations and the heat to our north-east slowly subsides.
This means we'll continue to see the influence of La Niña through this summer before we transition to a more average state of affairs for both surf and weather into next autumn and winter.
There are no clear surf signals for a neutral Niño 3.4 phase, however East Coast surfers should expect a less active swell season from the east (compared to the last two), while those in the southern states will hopefully see a return to normal programming through autumn and winter.