- Gulf inshore waters turn from cold to hot
- Is the Bay warm enough to go swimming?
- And the prize goes to … Crowdy Head
We are well into spring and SSTs are on the climb everywhere. The RAMSSA anomaly image shows that neutral and weak cool anomalies continue to the west and the south, however positive anomalies are developing along the east coast. A strong warm anomaly continues in eastern Victoria as discussed last week.
It is also warming up in the tropical north. Sea temperatures inshore are reaching 30 to 31 deg C at Darwin. These are the warmest waters in Australia at the moment, as the Indonesian Throughflow waters are further heated by insolation.
The warm water is contributing to hot weather conditions in the NT with two recent nights where the air temperature did not drop below 27 deg C. Heatwave warnings are in place for this week for much of the Top End.
flip in seasonal signature
A trigger for this warming in the north is that the winter production of cool inshore water in the tropics – seen clearly from June to August – has stopped.
Now we see very warm inshore waters.
Compare this to June.
Note also that the surface currents have reversed direction.
A recent paper by Wijffels et al (2018) demonstrates that a winter temperature front caused by cool inshore water dissipates in October. At this time of year the shallow waters inshore warm up rapidly.
The SSTAARS climatology for October confirms that the southwest of the Gulf warms the most, with the southeast corner lagging somewhat but still warming faster that the waters offshore.
The warm water front is much less sharp than the cool winter counterpart, even in February. Wijffels et al (2018) speculates that this is because of buoyancy effects. The surface current is southeastward in the Gulf in summer which is a direction associated with upwelling. Therefore the strong warming may be partially offset by cooler upwelled waters.
Swimming time in vic?
Port Phillip Bay is warming up, with surface temperatures now approaching 15 deg C. The ocean temperature outside the Heads lagged the Bay’s seasonal cycle, with a minimum value in September (compared to August inside the bay), but now both inside and outside temperatures are rising. Time for a swim?
‘record’ leap in sst’s at crowdy head
After the 2 degree increase in SSTs overnight at Eden two weeks ago, Crowdy Head in NSW is set to take a new record for biggest one day jump with a huge 5 degrees! (Note, this is a notional record invented by the author). The measurements leapt from 15.5 to 20 deg C in one day, with a further climb to 21 deg C the following day.
It is the lower temperature that was the anomaly: caused by localised upwelling during 5 days of continuous NE’ly winds associated with a high pressure system in the Tasman. For a while Crowdy Head had the coldest water temperatures in NSW – even colder than Eden.
Now the winds have eased and temperatures have recovered. The measurement of 21 deg C indicates that the buoy is sitting on the western edge of the main EAC flow (seen in yellow in the images below).
How could a bottle travel against the mean flow of the EAC? Two years ago a schoolgirl in Tasmania dropped a message in a bottle in Tasmanian waters and it was discovered in Queensland last month.
David Griffin and Madeleine Cahill from CSIRO have published an Ocean Current article that seeks to explain how this could happen. See the article and the model simulation here.