For the east coast, steady north-west winds tend to move the upper layer of the ocean to the east. Warmer surface waters are replaced by upwelling to cooler waters from below, which feel frigid for those who take a dip.
The reverse effect – downwelling that brings in warmer, more tropical waters from the East Australian stream – usually follows persistent southern winds.
"The last true southern road was spent over the weekend before Christmas," Hopkins said, adding that since then there have been persistent North Korean winds and swellings.
"Headaches from casting"
A spokeswoman for the Australian Coastal Society says beachers can often be stuck when hot air temperatures attracting people do not match when people throw themselves away.
"These are the times when [the cool water temperatures] are more noticeable, "he said, with likely for some to experience" headaches from milk "from a sudden cold.
Jordan Notara, the Weather Forecast for the Meteorological Bureau, said the next southern change is not expected to reach Sydney until Sunday.
"It's obvious that the air temperatures will decrease," he said.
Before that, however, Sydneysiders should have many reasons to consider traveling to the beach, especially on Friday and Saturday, when maximum forecasts are expected to reach 31 and 33 degrees, respectively. The western suburbs again need to see the lively climbing in the tall 30s.
"At the moment, the strength of the northwestern countries will be held or it will postpone that sea breeze [on Saturday]Said Mr. Notara.
The improvement of cold water has another consequence: the increased chance of getting a fog, like warm, humid air moves over the colder seawater.
Southeastern Australia will survive part of the most intense heat on Friday. "It looks like in the mid-40s through the river and the lower and upper western districts," he said.
Victoria can give her record temperature of 47.2 degrees of shaking, while Melbourne is expected to bake with heat of 42 degrees.
While coastal waters along the Sydney coast may look as if they are on a cool side, the same is not true for the greater part of the Tasman Sea.
The sea surface temperature is several degrees above the normal during this time of the year, according to the US National Oceanic and Atmospheric Administration.
Peter Hanam is an Environmental Editor at Sydney Morning Herald. It covers general environmental issues ranging from climate change to renewable energy sources for Fairfax Media.