Prosper in a dynamic world
Search

Why so windy?

Blustering winds have lashed southeastern Australia over the last few days, but it’s more than just a cold front adding to the wind strength.

Over the weekend, a strong cold front crossed through the south, delivering gusty winds and alpine snow. Some of the strongest winds recorded have been:

  • 122km/h Hogan Island (Vic) 
  • 111km/h Mount Buller (Vic) 
  • 109km/h Neptune Island (SA) 

And while these winds gusts are strong, something more interesting has happened in NSW. The strongest wind gusts recorded in the state over the last 24 hours are:

  • 100km/h Shellharbour and Nowra 
  • 98km/h Kiama 
  • 95km/h Montague Island Lighthouse 
  • 93km/h Thredbo Top Station

That’s right, locations on the Illawarra coast and adjacent inland have had stronger winds than an exposed lighthouse and the most elevated weather station in Australia at 1957m.

The powerful wind gusts near Nowra brought down powerlines and caused two fires to start and over 7000 residents to wake up without power this morning.

Those in Sydney and the South Coast of NSW have also had some strong winds. Sydney Airport and Port Kembla have both been dealing with sustained 28 knot winds, proving challenges for flights and ships alike.

Image: Forecast wind gusts for 1pm Monday. Reds indicate strong winds, with gales in purple

So why are the winds so strong at these normally calmer locations? It’s a process known as the downslope effect.

During the nighttime, the ground cools off faster than the air above it, meaning a temperature inversion forms. This inversion acts a strong barrier, keeping the air above and below it separate from each other. In locations like Sydney and the Illawarra, this inversion will link up to nearby mountain ranges, creating a strong barrier from winds that blow over the mountain.

However, once the sun comes up, it starts to warm the slope of the mountain, allowing the inversion to break down along the slope. With a gap now in the protective inversion, air can rush down the side of the mountains to the ground below. Since the gap in the inversion is small, air rushes down this gap faster than it would otherwise, turning strong winds into gales.

It is somewhat common for this to occur for the NSW east coast, including Sydney and the Illawarra, but this effect occurs throughout Australia anywhere where there is a mountain range. In Adelaide and Perth, this effect occurs in generally easterly winds, while northerly winds trigger the effect for Melbourne and Hobart.

Due to the increase in wind strength on the lee side of mountains, the downslope effect is a critical element in predicting the movements of bushfires, dust storms, air pollution and even blizzards.

The downslope effect has been instrumental in Monday’s powerful winds in NSW, but luckily, the protective inversion will start to build as the sun goes down, causing winds to ease. As the cold front moves further out to sea, high pressure will build, allowing calmer conditions to return.

DTN APAC mixes our expert knowledge, data inflows and artificial intelligence to convert our weather forecasts into a forecast of power outages through our Storm Impact Analytics (SIA). This system compares historical outages with a custom high-resolution forecast to determine where, when and how many power outages are expected during an event. To find out more about our services, please email us at apac.sales@dtn.com.

Latest news

Satisfy your weather obsession with these news headlines from around the nation, and the world.

Australia’s 2025-26 tropical cyclone names released

Australia’s 2025-26 tropical cyclone season is almost here and the names that will be used for cyclones throughout the season have been locked in. The Australian tropical cyclone season runs from the beginning of November to the end of April. During this six-month period, we usually see around 9-11 tropical cyclones in the Australian region, […]

Sydney’s 2nd-hottest September on record driven by rare stratospheric warming

Despite a brief cool spell early in the month which included Sydney’s wettest September day in 146 years, the harbour city has recorded its second-warmest September since records were first kept in 1858. In September 2025: Sydney’s average maximum was 23.5°C, which was around 3.3°C above the long-term average of 20.2°C. Sydney’s average minimum was […]

Brisbane’s driest September in 38 years drives elevated bushfire risk into October

Parts of southeast Queensland just had a remarkably dry start to spring, with Brisbane registering its driest September since 1987, increasing the risk of elevated bushfire danger into October. Rainfall was variable across Queensland in September as cloudbands and bursts of tropical moisture delivered healthy totals in the state’s southwest and northeast, while a broad […]

Much-needed rain spreads across Tasmania

Rain is falling right across Tasmania this Tuesday, in a continuation of the welcome wet weather streak of recent weeks. Prior to September, Tasmania had experienced a very dry first eight months of 2025, with rainfall totals the lowest on record in some areas. Widespread light falls dampened much of Tasmania on Monday night into […]