- A ship suffers from ‘rough seas’ in EAC
- Leeuwin Current keeping the south warm
- Coastal inundation in WA
The north has cooled and now a widespread small negative anomaly can be seen across the northern states and extending to Indonesia. This is likely due to a break in convection causing good radiative cooling during the last couple of weeks.
Meanwhile the 2 deg C warm anomaly off Albany in southwest WA has expanded after prolonged northerly winds ahead of a cold front reinforced the Leeuwin Current and pushed more warm water to the south. The Leeuwin Current extension can be seen in a warm anomaly all the way along the SA coast, down the western TAS coast, where it joins a warm eddy to the southeast of Tas.
The eddies of the Leeuwin Current off WA have strengthened and become more active as we move into the winter season. By the end of this week we should see four warm eddies along the continental shelf edge, roughly in line with Exmouth, Shark Bay, Geraldton and Perth. The strongest eddy is off Geraldton and is about 100 nm wide. It shows a SLA of 0.5 m and has associated geostrophic currents of 1.5 knots.
A series of cold fronts, with associated pre-frontal northerly winds and post-frontal surge, have caused elevated sea levels along the WA coast. During particularly strong cold front yesterday these effects combined with large onshore waves to cause coastal flooding. The rare NW’ly wave direction concentrated the sea level event in Geographe Bay, as shown in the pictures below.
Currents associated with the EAC and the warm eddy off Sydney claimed a victim last week when the container ship YM Efficiency struck rough seas about 15 to 20 nm off the coast of Port Stephens. The ship lost dozens of containers overboard which now present a hazard to mariners.
On the 31st of May, southward currents of 1 to 1.5 knots were met with opposing large waves from the south. Significant wave heights of 6 to 7 m were forecast offshore. The wave buoy at Sydney Heads showed a rapid increase in sea state from Hs of 2 to 3 m, to 5 m by Thursday evening. Maximum wave heights of 9 m were recorded. These conditions were well-predicted by the models (as discussed last week) but it is not known if the ship was forewarned and what happened to cause the containers to be lost.
When currents meet waves from opposing directions, the sea roughness increases. Wave are more likely to be breaking. Also, significant wave heights can be larger than the wave forecast. Furthermore, studies have shown that the statistical distribution of wave energy changes in opposing currents and rogue waves can be more frequent.