East coast lows

East Coast Lows are intense low pressure systems that often produce severe weather, and as the name suggests they form off the east coast of Australia, in fact in all of the New South Wales coast, southeast Queensland coastline and far eastern Victoria, and sometimes Tasmania.

Australia's regularly impacted by normal lows and cold fronts, they're transient in nature and they sweep through and their effects are fairly short-lived. In contrast to that, East Coast Lows can be quite slow-moving or even near-stationary, and that means their effects can last much longer. So they do produce prolonged periods of heavy rainfall which does lead to both flash flooding and flooding of the major rivers, they produce damaging wind gusts, and with the wild winds they whip up very large seas which can lead to coastal erosion, and when it coincides with high tides even local coastal inundation. And all of these conditions are hazardous, including for marine users. East Coast Lows form in a variety of ways; they can be associated with cold fronts or coastal troughs, or even ex-tropical cyclones as they decay and move south. But some of the most powerful ones that we've seen throughout our history are associated with a fairly complex interaction with the upper atmosphere as well.

The development generally starts when some cold air that's well down south of Australia normally starts to push up over New South Wales/Victoria, and above all of that cold air in the middle and upper parts of the atmosphere becomes separated and slow-moving over New South Wales. Now ahead of that bubble the atmosphere is generally rising ahead of it, and as it comes far enough east and interacts with the East Australian Current which brings relatively warm water off the east coast, we start to see a low pressure develop off the east coast of Australia. Now as these two systems interact, that low pressure begins to intensify and deepen, and that starts to lead to wilder weather on the coastline. Sometimes we have high pressure to the south cradling this system, and the effects of the winds flowing out from the high and also with the low really converges in on the southern flank, causing the weather to be much worse on the south side of these East Coast Lows. Now these wild winds sweep in off the coastline bringing the moisture with them, and it flows up and over the Great Dividing Range and as it does so it releases all of the rainfall and that's where the flooding concerned can come from.

The peak season for development is the late autumn and winter period, however we can see East Coast Lows all year round and the eastern seaboard typically sees multiple events every year and they range in their intensity and severity. We often get asked how East Coast Lows are different from tropical cyclones and that's because sometimes the impact and the way they look on radar can be fairly similar. But they're a completely different weather system and they form in different ways. Tropical cyclones need the warm tropical water to survive, whereas East Coast Lows don't and that's why they can form so much further south. In terms of strength, East Coast Lows the really intense one can produce winds of strength of Category 1 or even a Category 2 cyclone. They're generally a little bit more short-lived than a tropical cyclone, but in terms of their peak intensity they can be fairly similar to a tropical cyclone.

Because East Coast Lows produce such dangerous severe weather it's really important to have a pre-prepared plan for how you and your family will stay safe during these events, and if you hear the term 'East Coast Low' in the media it's a really key time to tune into the latest forecasts and warnings, and listening to advice from emergency services can be critical to being prepared and staying safe.