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Sydneysiders are flocking to the beach this month as the sun returns in full force following the city’s wettest year on record. Beachgoers, however, are in for a shock.
Sea temperatures are a brisk 18 degrees at the coldest times of November – a month that usually records an average sea temperature of 21 degrees.
Temperatures around the mid-20s tend to be comfortable for the average beachgoer, but it depends on factors including the type of swimming and a swimmer’s age and body composition. Children and older adults may be more comfortable swimming in higher temperatures between 27 and 30 degrees.
Marley Durrans and Asha Lia-Lorenz cool off at Clovelly after their HSC exams.Credit:Janie Barrett
The sun and sea currents are to blame for the chilly swimming experience. Professor of coastal oceanography at the University of Western Australia, Charitha Pattiaratchi, says they are the main factors behind sea temperature. “If you have several days of cloud-free hot days, then the coastal waters will become warmer,” he says. “And if you have an episode of the East Australian Current close to the coast, then that will also enhance the warmer waters.”
The film Finding Nemo cemented the importance of the East Australian Current as a superhighway transporting fish and sea turtles down to Sydney Harbour. More generally, it is a warm current that starts just south of the equator and travels down the east coast of Australia.
Pattiaratchi compares the current’s movement to a dog wagging its tail. “The current is always there, but sometimes it will come close to the coast, and sometimes it will be further away,” he says.
The East Australian Current brings warm water down to Sydney.Credit:Integrated Marine Observing System
The flow of river water, strengthened by floods, also has an impact – especially closer to the shore. “River water is usually colder and lower salinity than ocean water,” Pattiaratchi says. Fresh water often feels colder than sea water because it contains less salt.
Marley Durrans and friend Asha Lia-Lorenz dived into Clovelly Beach on Tuesday morning after finishing their exams. “We’ve just finished out HSC, so we’ve been going to the beach every single day,” Lia-Lorenz says. “The sun is scorching, but it’s quite cold in the water, so it takes a minute to adjust, but it’s very refreshing.”