A weather station in Tasmania has just recorded what could be the highest mean sea level pressure on record in Australia.
According to data from the Bureau of Meteorology, a weather station at Ouse, Tas registered a mean sea level pressure of 1044.5 hPa shortly before 10 am AEST on Monday, July 6, 2026. This is provisionally the highest mean sea level pressure on record in Australia, beating the previous record of 1044.3 hPa at Launceston on June 7, 1967.
What is mean sea level pressure?
The term mean sea level pressure (MSLP) refers to the atmospheric pressure adjusted to Earth’s mean sea level at a given location. It is calculated by taking observed air pressure at the Earth’s surface and then adjusting it to what the pressure would be at Earth’s mean sea level.
MSLP is commonly used by meteorologists because it normalises air pressure to a single level, allowing pressure systems to be compared and mapped across the planet on a synoptic chart.
Areas of high MSLP are referred to as high pressure systems and are usually associated with calm and dry weather. Air descends towards the surface at the centre of high pressure systems, which is why the surface pressure becomes higher relative to the surrounding atmosphere.
By contrast, areas of low atmospheric pressure – commonly referred to as low pressure systems – are characterised by rising air, low surface pressure and stormy weather conditions.
Image: Modelled mean sea level pressure over Tas at 10 am AEST on Monday, July 6, 2006. Source: Weatherzone.
Why was the air pressure so high in Tasmania on Monday?
Monday morning's provisional mean sea level record occurred as the centre of a strong high pressure system sat directly over Tas. This high pressure system has been intensified by a deep low pressure system sitting over the Tasman Sea, due to a process called anticyclonic intensification:
The low pressure system over the Tasman Sea rapidly intensified on Sunday and Monday while located to the west of New Zealand.
Rising air inside this low moved away horizontally once it reached higher altitudes – a process called divergence.
The air escaping the low’s upper levels flowed into the upper-levels of high pressure system – a process called convergence – where it then descended towards the surface – also called subsidence.
How will this strong high pressure system influence the weather?
The clear and calm conditions at the centre of the strong high pressure system caused bitterly cold temperatures on Monday morning. This included Melbourne dropping to 3.2°C, which was its coldest morning so far this year, while Coldstream hit -2.7°C. In Tas, Liawenee’s temperature plunged to -8.1°C shortly after 7 am on Monday morning.
Monday’s provisional record-breaking high pressure also meant there was more air sitting above Tasmania. Compared to the global average mean sea level pressure of around 1013 hPa, Monday’s 1044.5 hPa meant there was about a 3% increase in air mass sitting above Ouse. So, if you were feeling a little weighed down on Monday morning, you can blame it on the extra air sitting above your head.