03 May – Southern sea level surge


There are signs that waters around the country are starting to cool down, albeit ever so slowly. The anomaly in the northwest has decreased and now the waters sit at about 30 degrees C. This is still very warm, obviously, at 1.5 degrees C above the RAMSSA climatology. It looks like this heat has been mostly lost due to radiative cooling.


Daily SST anomaly – RAMSSA

To get a feel for the extent of this heat depth-wise, we can look at a transect along the North West Shelf. The image below shows the 95 percentile anomaly – ie. the amount the temperature exceeds the 95% value. It is not seasonally dependent, the statistics are from the whole BRAN dataset. We can see that some unusually warm water is sitting at 40 to 50 m depth. (While the SST is warm for this time of year, the actual values are not extreme. The percentile exceedance shows anomalies for the whole year).


OceanMAPS transect of 95 percentile of potential temperature

A temperature profile (below) indicates that the mixed layer extends down to 50 m; so it is the depth of the mixed layer that is unusual. Therefore even if the sea surface is starting to cool, it will take a long time for this whole layer to cool (the  warmth at depth may help sustain the surface anomalies for longer than otherwise). Or, we may see the MLD becoming shallower over time.

Potential temperature profile


Sea levels will surge along southern Australia today as a low pressure system in the Great Australian Bight pushes water up against the coast. Up to 0.8 m of surge is expected inside the Spencer Gulf. This effect is amplified by the spring tides at the moment, a few days after the full moon.

Aggregate sea level viewer showing detail at Port Pirie

A coastally trapped wave (positive sea level anomaly) will be generated in WA on Sunday as ex-TC Flamboyan approaches Perth. This will quickly propagate around the southern coastline towards the eastern states. We have seen a few of these events in recent weeks. They can travel faster that the weather systems that generated them, causing local sea levels to rise ahead of any directly-forced storm surge.

Sea level anomaly T+72
Sea level anomaly T+96
Sea level anomaly T+120


Now a brief check in with the salinity around the country. In the image below we can see the most saline parts of the greater ocean are sitting between 25 and 35 S. A typical value at the surface here is about 35 PSU. Further north, the water is fresher (32 to 34 PSU) in the Gulf of Carpentaria and near Indonesia due to higher rainfall. It is most saline inside the shallow Spencer Gulf due to evaporation. Values reach up to 40 PSU in the north part of this gulf. If you look closely you can also see the salinity signature of the boundary currents. Fresher water is pushed down the NSW coastline in a narrow sliver due to the East Australian Current. On the west coast the Leeuwin Current is also visible as slightly fresher.

Salinity (PSU)



2 thoughts on “03 May – Southern sea level surge”

  1. In the long run we are all dead. Economists set themselves too easy, too useless a task, if in tempestuous seasons they can only tell us, that when the storm is long past, the ocean is flat again.
    A Tract on Monetary Reform (1923), Ch. 3, p. 80

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