It'll be no surprise to Sydney-siders - who've been in boardshorts since last November - that the sea surface temperature record was broken two days in a row at the start of the month.

The Manly Hydraulics Laboratory’s Sydney wave buoy, which is situated approximately 10km off of Long Reef, hit 26.75°C on both Wednesday the 8th and Thursday the 9th of March, breaking the February 2022 record of 26.6°C.

Meanwhile, inside the surf zone it's been hovering between 23-24°C.

Sea Surface Temperature observations off Long Reef, Sydney, since 1993. Note the red trend line and record 26.75°C temperature marked by the red dot. (MHL)

Further out to sea, temperatures were even higher, reaching 27°C as a warm tongue of the East Australian Current protruded south. To the north it's even warmer, sitting at 28°C offshore from Yamba and Byron Bay, resulting in oppressive humidity, only broken today by the first proper incursion of cold air from the south.

Humans regulate our body temperature through sweating and evaporative cooling. The relatively drier air around us helps transfer heat away from the body through the process of evaporating sweat.

But when this air is itself highly saturated, then the process becomes less efficient, even to a point where it doesn't work at all and we start to overheat. This is the issue confronting many with the warming oceans.

Sea Surface Temperature observations off the Southern NSW coast (March 4th). (BOM)

But how does warmer water increase the humidity?

Again, by the simple transfer of energy. The warmer the water, the greater the rate of evaporation, transferring water molecules into the adjacent air mass as water vapour.

This makes the coastal air mass more humid, which in turn creates increased humidity anywhere east of the dividing range, where the humid air becomes effectively trapped.

The below chart shows the precipitable water anomaly for the past three months.

Precipitable water is a good proxy for humidity as it shows the amount of available water in the atmosphere for possible rainfall. The higher the values, the more saturated the atmosphere, while the lower the values, the drier it is.

The anomaly shows the difference from the long-term climatic mean (1991-2020) and what stands out is the increased precipitable water values off the East Coast (on top of already humid weather expected through summer). Also note the dry slot off Western Australia, driven by persistent inland south-easterly winds. This lead to Western Australia experiencing their hottest summer on record.

Precipitable Water anomaly for the past summer. (NOAA)

It's not just the East Coast that's experiencing warmer than normal temperatures, Tasmania has been very mild in the ocean thanks to the extension of the East Australian Current pushing down their East Coast, making it into Storm Bay (2-3°C above average). Bass Strait has also seen temperatures coming in 1-2°C above the long-term average.

This is following an El Niño year, which typically brings cooler sea surface temperatures to Australia, yet this time the trend was bucked with global temperatures coming in at their highest on record during 2023.

There have also been multiple reports of tropical species making their way further south with the currents. A highly venemous yellow-bellied sea snake washed up at Manly earlier this week (see left - photo thanks to Philip Eastburn), with another making it all the way to Pambula last November. Another account was of a green turtle that made its way into Hobart's River Derwent at the end of January.

Looking ahead, and the East Australian current still has a plentiful supply of warm water from the Coral Sea and this should maintain warm sea surface temperatures well into the second half of autumn. It'll just be a matter of donning a wetty top to keep the cooler air temperatures at bay.

Special thanks to Manly Hydraulics Laboratory for the collection and provision of wave and sea surface temperature data on behalf of the NSW Department of Climate Change, Energy, the Environment and Water.