11 Oct – Where are the LC eddies now?


Sea surface temperatures are still cool off southwest WA, at 2 deg C below average in places. Frequent cold fronts and southerly winds – pushing well-mixed southern ocean water northward – have contributed to the sustained cool anomaly. Meanwhile the Leeuwin Current weakens inshore after peak strength in the early winter.

SST Anomaly for Australia – RAMSSA

On the other side of the country we see warm anomalies, especially around Gabo Island in Eastern Victoria. Temperatures there are 2 deg C above normal.

SST Anomaly for VIC/TAS – RAMSSA

In fact, water temperatures at Eden jumped 2 deg C overnight last Saturday the 6th of October  – from 15.5 deg C to 17.5 deg C as a tongue of warm EAC water pushed southward along the coast. Now it is hovering around 18 deg C, with warmer water further offshore.

A veritable Garden of Eden?

SST for Eden, NSW – Source: Manly Hydraulics Lab
SST forecast for NSW for 5th October – OceanMAPS
SST forecast for NSW on 11th October – OceanMAPS

The temperatures inshore may temporarily drop again next week  as strong NE’ly winds over the weekend bring some local upwelling.

SST forecast for 17th October – OceanMAPS


Low sea levels are expected along southern coasts today and Friday due to E to SE’ly winds causing Ekman transport away from the shore.

Wind speed and direction for Thursday the 11th October – ACCESS-R
Sea level anomaly for Friday 12th October – OceanMAPS

The sea level viewer is showing a chance of water levels being below Lowest Astronomical Tide (LAT) Portland, and very close to LAT elsewhere in SA and VIC.

Aggregate sea level forecast and observations for Portland – Sea Level Viewer



Have you been wondering what happened to those Leeuwin Current eddies that were spawned in June?

The image below shows what they looked like then:

Sea level anomaly in WA for 26th May and 12th June – OceanMAPS

Now most of the warm eddies are weak and well out to sea. Only one eddy remains strong and we can see it disappearing westward off the map:

Sea level anomaly for WA on 11th October – OceanMAPS

The strong warm eddy at 108 E is the old eddy that was west of Geraldton in June. This was an anomalously strong eddy that was 120 nm wide, had a sea level anomaly of 0.5 m and associated geostrophic currents of 1.5 knots. Now it has shrunk a little to 85 nm wide, with a sea level anomaly of about 0.3 m and geostrophic currents up to 1.0 knots.

The eddie’s movement has been wobbly. Using the webviewer we can track the eddy over the past few months – see image below. It seemed to move northwest initially, before moving southwestward in late August and then has moved mostly westward since then.

SSH for central WA shown in monthly snapshots Jun to Oct, with arrows in last panel showing monthly movement – OceanMAPS – Click to enlarge

According to academic studies, LC eddies have a mean westward speed of 2.6 km/day. Warm eddies have been shown to have an equatorward component of 0.4 km/day, but cold eddies move poleward at 0.8 km/day.(Morrow et al 2004)

Propagation of (a) warm and (b) cold core eddies of the Leeuwin Current, coloured by relative vorticity. Credit: Morrow et al 2004

Has this warm eddy moved in the way we expect? Unfortunately for tracking purposes the eddy’s position is becoming more uncertain as it weakens. The last three runs of OceanMAPS put the eddy in three slightly different places.

SSH for central WA from the last three runs of OceanMAPS, bottom right shows the standard deviation of the ensemble – OceanMAPS – Click to enlarge

Let’s take the ensemble mean position of the eddy from the last three runs, and see how fast it has moved since June.

On the 1st of June the eddy was centred at: 29.2 S 112.5 E
On the 11th of October the eddy is centred somewhere near: 29.4 S 109.3 E

That’s 0.2 degrees southward  = 22 km / 12 nm
And 3.2 degrees westward at 30 S = 307 km / 166 nm

Over the span of 133 days between the two dates, an average warm core eddy would travel 53 km northward and  345 km westward. So this eddy’s path has gone slightly poleward instead of equatorward and also moved westward a little slower than normal.

Will it now pick up the pace and start running?


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