Verification of a poor East Coast autumn: Take 2
Autumn 2019 on the East Coast was a particularly poor season. We made that argument in an article last month, but howsabout another layer of data just to put the case beyond doubt?
Yeah. Why not...
If you recall, we looked at looked at the monthly wind and pressure anomalies (the difference from the long-term climatological mean) for March and April and it confirmed what most East Coast surfers had been thinking. This autumn was poor with persistent onshore winds and small swells, while on the other hand Victoria and South Australia had a great run with good persistent swells and favourable winds.
Well, we've just got the data back from May and it reinforces the data from March and April.
Across the entire Tasman Sea we've seen winds generally from the north to north-west, not conducive to swell production at all, while a positive westerly wind anomaly can be seen in the Bight and across Victoria, relating to their consistent run of clean fun surf.
Over in Western Australia a strong positive pressure anomaly has lead to fine, clear weather and persistent offshore winds, favouring spots like Margaret River.
What we can take from this is that is that the unusual weather wasn't a month-long anomaly, but it enveloped the whole season. The pattern bedded down across the continent for the better part of a quarter of a year.
So now we've explained away the past autumn, what's in store for the coming winter?
Unfortunately, there are too many influences on our surf climate to nail down a specific trend ranging from what the Southern Annular Mode (SAM) is doing, where the Long Wave Trough is focussed, whether we're in El Nino or La Nina, and also granular details such as regional water temperatures.
For the East Coast there have been studies conducted showing the cause and effect on sea heights in the Coral and Tasman Seas in relation to El Nino and La Nina. During La Nina we see an increased in swell activity, while during El Nino we see the opposite.
We're currently on El Nino watch which means we're not quite at the threshold for a proper El Nino event and even if it does reach it, it will be weak and short-lived. This doesn't bring us any closer to an outlook for the coming winter on the East Coast. It's currently pumping across selected spots, but this is owing to the Long Wave Trough moving through.
For the other states it's even more flukey to make a prediction. The SAM influences how far north or south the storm track is: when it's negative it's pushed further north over the country, and when positive, further south and away.
It's currently weak positive and is forecast to remain so for the coming fortnight or so, which is why we're currently seeing a small run of surf. Forecasting the SAM beyond this is near impossible so you'll have to keep an eye on the local Forecaster Notes over the coming months.