April 13, 2010

Goodbye severe storms, hello East Coast Lows

With the onset of the cooler autumn weather, the chance of severe thunderstorms impacting the Gold Coast and South-East Queensland drops quite low.

However, it doesn't mean that we aren't out of the woods in regards to severe weather activity - the East Coast Low.

What is an East Coast Low (ECL)?:

According to the Bureau of Meteorology, East Coast Lows are intense low-pressure systems which occur on average several times each year off the eastern coast of Australia, in particular southern Queensland, NSW and eastern Victoria. Although they can occur at any time of the year, they are more common during Autumn and Winter with a maximum frequency in June ... and will often intensify rapidly overnight. East Coast Lows are also observed off the coast of Africa and America and are sometimes known as east coast cyclones. (Source: BOM)

What's the difference between an East Coast Low and a Tropical Cyclone?

Tropical Cyclones develop over very warm tropical waters where the sea surface temperature is greater than 26°C. They have relatively long life cycles, typically about a week, and severe tropical cyclones (category 3 or greater) can produce significant property damage with wind speeds over 180km/h near the centre, heavy rainfall and coastal inundation through storm surge.

East Coast Lows generally have much shorter lifetimes than Tropical Cyclones and last only a few days. They develop over the Tasman Sea close to the coast and can intensify rapidly in the overnight period. Unlike Tropical Cyclones, where the warm seas provide the energy source, East Coast Lows are driven by the temperature gradient between the Tasman Sea air and cold air in the high levels of the atmosphere over the continent.

They can produce gale to storm-force winds, very heavy rainfall and in some cases coastal inundation. While maximum wind speeds recorded are lower than in severe tropical cyclones, a gust of 165 km/h was recorded at Newcastle associated with the east coast low that sunk the bulk carrier Sygna in 1974. During the first of the ECLs in June 2007, when the bulk carrier Pasha Bulker ran aground, gusts of 105 km/h at 6:21am on 8 June and 124 km/hr at 1:32am on 9 June were recorded at Newcastle. (Source: BOM)

When did the last major East Coast Low affect the Gold Coast?

For those of you on the Gold Coast last year on May 20th 2009, an intense East Coast Low produced heavy rain and strong winds resulting in flooding, large seas and storm damage across the south-east corner, with a man killed by flying debris in Surfers Paradise whilst he sat in his office.

From The Weather Chaser's (http://www.theweatherchaser.com) impressive and extensive archive of BOM Radar images, we can go back in time to view what was actually on the radar and view as an entire loop between 18th May 2009 to 22nd May 2009.

Picture 1 below from the 128km Mt Staplyton (Brisbane) Radar Loop shows the intesity of the rainfall leading up to the the May 20th event. Whilst technically not a 'cyclone' within the images, a rotating circular formation (similar to an eye of a cyclone) can be seen crossing the Sunshine Coast around 10:30am heading south through Brisbane around 11-11:30am with the leading edge of the circular formation passing through the Gold Coast between midday and 2pm.

Picture 2 below from the 128km Mt Staplyton (Brisbane) Doppler Wind Loop shows the most intense, strongest winds crossing near Southport and Surfers Paradise at around 2-3pm when the southern edge of the 'circular formation' crosses the Gold Coast. Similar to Tropical Cyclones, the southern front is generally the strongest and most damaging when it comes to winds.

Picture 1: 128km Radar Loop for Brisbane Radar
for May 18th-22nd 2009
(Source: theweatherchaser.com)

Picture 2: 128km Doppler Wind Loop for Brisbane Radar
for May 20th 2009 between 10am-8pm
(Source: theweatherchaser.com)

An excellent, detailed explanation of how this particular East Coast Low formed, along with photo's and video's of it's effects can be found at the coastalwatch.com website.

Other major East Coast Lows in recent history that have affected the Gold Coast include:
  • the June 2005 event which caused localised flooding and landslips at Currumbin Hill
  • the March 2004 event which caused localised flooding and widespread power outages
So, at anytime between now and the end of June, we are likely to see another East Coast Low somewhere off Australia's eastern seaboard, but we'll have to wait and see if it affects us.

Do you remember or have a story relating to any of these events? Leave us a comment!