East coast lows

What is an east coast low?

East coast lows are one of Australia's climate influences. Some of our worst maritime disasters are caused by the destructive winds, torrential rainfall and rough seas that come with stronger east coast lows.

These intense low pressure systems happen, on average, several times each year off the continent's eastern coast. Particularly, in southern Queensland, New South Wales and eastern Victoria.

They can occur at any time of year but are more common during autumn and winter, most frequently in June.

East coast lows often intensify quickly over 12–24 hours. This makes them one of the more dangerous weather systems to affect the eastern coast.

They also happen off the coast of Africa and America and are sometimes called east coast cyclones.

Video: Ask the Bureau: What is an east coast low?

How east coast lows form

East coast lows can form in a range of weather situations.

In summer, they can develop from ex-tropical cyclones as these decay and move south.

At other times of the year, east coast lows often develop rapidly just offshore. This can happen within an existing trough of low pressure, due to favourable conditions in the upper atmosphere combined with warm sea surface temperatures.

East coast lows may also develop in the wake of a cold front moving across from Victoria into the Tasman Sea. The warm sea surface temperatures associated with the East Australian Current are also an important factor contributing to the development of the systems. The sea surface temperature gradients associated with the warm eddies of the East Australian Current help the lows develop.

Gales and heavy rains can often occur on and near the coast south of the low centre, while there can be clear skies to the north of the low. The challenge for forecasters is to accurately predict the location, movement and intensity of the centre of the low.

How often east coast lows form

Each year there are about 10 east coast lows that have significant impact. We generally only see 'explosive' development about once a year.

Looking at all the lows detailed in our database since 1973, there is no evidence of a trend.

Why east coast lows are dangerous

East coast lows can create one or more of:

• gale or storm force winds along the coast and adjacent waters
• widespread heavy rainfall, leading to flash flooding and major river flooding
• very rough seas and prolonged heavy swells over coastal and ocean waters, which can damage the coastline.

During past east coast lows:

• falling trees and flash flooding have caused loss of life
• many small craft have been lost off the coast
• larger vessels have run aground.

Pasha Bulker was grounded on a reef just off Nobby's Beach near Newcastle, NSW, by an east coast low in June 2007. Credit: Brett Delaney, ex-Bureau weather observer.

Differences between east coast lows and tropical cyclones

Tropical cyclones develop over very warm tropical waters where the sea surface temperature is greater than 26° C. This gives them a unique structure and behaviour, very different from an east coast low. They have relatively long life cycles – typically about a week.

Severe tropical cyclones can produce:

• significant property damage with wind speeds over 180 km/h near the centre
• heavy rainfall
• coastal inundation (flooding) - through storm surge.

East coast lows can produce:

• gale to storm-force winds
• heavy rainfall
• in some cases, coastal inundation.

While maximum wind speeds recorded are lower than in severe tropical cyclones, significant gusts have been recorded at Newcastle:

• in 1974, a gust of 165 km/h associated with the east coast low that sunk the bulk carrier Sygna
• in 2007, gusts of 105 km/h at 6:21 am on 8 June and 124 km/h at 1:32 am on 9 June when the bulk carrier Pasha Bulker ran aground. This was the first of 5 east coast lows that year.

For more information about cyclones, view our Tropical cyclone knowledge centre.

Severe weather warnings

View the National warnings summary.