With a forecast of 42 degrees in Sydney's west and 33 degrees for the city today, you'd be forgiven for thinking that it's a perfect beach day for enjoying Australia Day! Afterall, it's set to be the city's hottest Australia Day in 31 years and Penrith's hottest day all summer!
But while it's turning out to be an absolute scorcher, the hot tropical airmass that's causing all of this heat has also contributed to a strange thick sea fog across some of Sydney's most popular beaches, on what is arguably one of Sydney's most popular beach days of the year!
So how has this sea fog formed?
Well, sea fog is also known as "advection fog" which refers to the movement of warmer air over a cooler surface. The hot airmass which is being drawn in from the tropics to Sydney today by northerly winds (and causing Darwin-like humidity!) has been carried over the cooler waters of our beaches. Now the contact of this hot and humid airmass with the colder water has caused the air directly above the sea surface to cool. Cooling of the air causes the water vapour in the air to condense into liquid droplets which we see as fog! It also helps that the winds are light so there's nothing to push the fog away.
When will it go away?
Later today when the sea breeze develops winds will tend N/NE'ly blowing the fog parallel to the coast, so visibilty should improve. Winds will also become stronger which should enhance mixing of the lower atmosphere, helping to dissipate some of this fog, although it could remain hazy. We have a southerly change coming in this evening which will bring a "relatively" cooler and drier airmass through Sydney so sea fog is less likely tomorrow. I say "relatively" because this southerly won't bring much of a temperature drop to Sydney tomorrow. It's not until Friday that temperatures will become more bearable with a forecast 25 degrees for the city and 27 degrees for Penrith.
But while it's turning out to be an absolute scorcher, the hot tropical airmass that's causing all of this heat has also contributed to a strange thick sea fog across some of Sydney's most popular beaches, on what is arguably one of Sydney's most popular beach days of the year!
So how has this sea fog formed?
Well, sea fog is also known as "advection fog" which refers to the movement of warmer air over a cooler surface. The hot airmass which is being drawn in from the tropics to Sydney today by northerly winds (and causing Darwin-like humidity!) has been carried over the cooler waters of our beaches. Now the contact of this hot and humid airmass with the colder water has caused the air directly above the sea surface to cool. Cooling of the air causes the water vapour in the air to condense into liquid droplets which we see as fog! It also helps that the winds are light so there's nothing to push the fog away.
When will it go away?
Later today when the sea breeze develops winds will tend N/NE'ly blowing the fog parallel to the coast, so visibilty should improve. Winds will also become stronger which should enhance mixing of the lower atmosphere, helping to dissipate some of this fog, although it could remain hazy. We have a southerly change coming in this evening which will bring a "relatively" cooler and drier airmass through Sydney so sea fog is less likely tomorrow. I say "relatively" because this southerly won't bring much of a temperature drop to Sydney tomorrow. It's not until Friday that temperatures will become more bearable with a forecast 25 degrees for the city and 27 degrees for Penrith.
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