Analysing Winter 2022
Stop, breath, reflect.
Without trying to sound repetitive or disrespectful to our southern brethren, the last three years on the East Coast have been an absolute surf binge. The seasons hardly mattered, be it spring, summer, autumn, or winter, it feels like it's rarely been flat in nearly three years of surf.
Autumn and winter are always generally reliable on the East Coast but the main difference through the last few winters has been the lack of large southerly swells. Breaking from seasonal norms, most of the swells have arrived from a more easterly angle.
And this is all thanks to the persistent La Niña signal throughout the Pacific Ocean which developed through 2020 and will enter its third year into the coming 22/23 summer.
So why does La Niña bathe the East Coast in endless swell?
Here's a refresher for those who need it but for those who don't and want to dive straight into the article you can scroll straight to the first surf photo:
- When stronger than normal easterly trade-winds blow across the equatorial Pacific Ocean (read: along the equator), we see warm surface water pushed to Australia's northern coastlines.
- Conversely, cold water is upwelled by the easterly trade-winds throughout the central and eastern equatorial Pacific Ocean, setting up a difference in pressure.
- The warm water north of Australia heats the atmosphere directly above it, causing it to rise, which in turn creates lower surface pressure. The opposite occurs over the cooler water, with descending air creating higher surface pressure.
- Winds flow from high pressure to low pressure - so from the cooler water in the east to the warmer water in the west - strengthening the easterly trade-winds further which in turn creates more upwelling to the east while piling up more warm water to the west. A classic positive feedback loop.
And that's not all.
- The flow on effects of the lower than normal pressure developing to the north of the country is a shift in the sub-tropical high pressure cell to further south than normal.
- This shift southwards opens the East Coast to swell-generating easterly trade-winds which are usually restricted to more northern locations. We also see the lower than normal pressure squeezing the high, generating stronger than normal trades. A win/win for the East Coast but the big losers of this setup at the southern states.
- The reason for that is that, just as the sub-tropical highs are pushed south, so to is the westerly storm track. It's shoved further south towards Antarctica, effectively suppressing it through autumn and winter.
- Instead of the normal Southern Ocean storms through the Roaring Forties we see less favourable swell producers in the form of mid-latitude lows and fronts. These mid-latitude systems sit too far north and have no sting in their tails to generate much beyond weak, short-period westerly swells.
- Being that winter is prime time for Victoria's Surf Coast and South Australia's Victor Harbor, swells arriving from the west are blocked by Cape Otway and Kangaroo Island respectively, resulting in clean but very small surf.
- The spawning ground for these mid-latitude systems is to the west-southwest of Western Australia, with the Margaret River region bearing the brunt of the storms resulting in weeks of onshore winds and large, stormy surf.
- The big winners are the WA metro regions as they're just north enough to be clear of all but the strongest fronts which results in lighter winds, cleaner conditions and plenty of swell.
OK, with that short refresher done, let's come up to date for winter 2022.
The following graph charts the Mean Sea Level Pressure anomaly (the difference from the long-term average 1991-2020) for the past three months.
What's most obvious is the higher than normal pressure sitting across the Furious Fifties and the Screaming Sixties, the engine room for Southern Ocean cold fronts and the swell farm for South Australia and Victoria.
We can also see the higher than normal pressure to the east of New Zealand which is linked to the La Niña signal which slowly decayed through autumn before re-strengthening into winter.
Lower than normal pressure hugs most of the Australian continent, with the negative Indian Ocean Dipole event (warm water build up around eastern Indonesia) being the cause of the lower than normal pressure to our north-west and west.
Looking at the wind speed and direction anomaly (again, the difference from the long-term average) we can see the source of the persistent easterly swell across south-east Queensland and northern NSW. That being the interaction between the high sitting east of New Zealand and lower pressure north of it, bringing stronger than normal easterly trades.
Also, note the stronger than normal easterly trade-winds across the equatorial Pacific Ocean, leading to a strengthening of the La Niña signal through the winter months.
For southern NSW, a steady diet of easterly swell energy was seen, with a few bigger days thrown into the mix thanks to the development of coastal and Tasman Lows. As touched on above this is at odds with normal winter seasons where we see southerly energy being dominant.
Personally, the convenience of surfing locally at Manly instead of heading further north over the hill, as is often the case in winter, was more than welcome.
The downside to all this easterly swell energy following two previous La Niña years was the erosion witnessed across nearly all beaches, some of it the worst in recent memory.
For the southern states, seeing south-southeast wind anomalies right across Victoria's main swell window is telling. This doesn't mean that winds were persistently south-east, just that the normal zonal, westerly breezes were absent and much weaker than normal.
The source of larger, long-period groundswells for Indonesia and Western Australia, that being the Heard Island region was very subdued (represented by the strong east wind anomalies in that area). This indicates winds in that region which are generally westerly were considerably weaker than normal.
And for Indonesia, the unfavourable NW winds across Sumatra, linked to the negative Indian Ocean Dipole, is clearly evident.
Moving into the spring and summer ahead, with our third La Niña summer locked and loaded, we'll be looking at favourable surf continuing across the East Coast along with a continuation of mid-latitude activity for the southern states.
Most agencies have the La Niña signal breaking down into the end of summer but we'll continue to monitor this closely.