Australian east coast low

An East Coast Low on 25 June 2013

Australian east coast lows (known locally as east coast lows and sometimes as east coast cyclones^[1]) are extratropical cyclones.^[2] The most intense of these systems have many of the characteristics of subtropical cyclones.^[3] They develop between 25˚ south and 40˚ south and within 5˚ of the Australian coastline,^[1] typically during the winter months.^[4][5] Each year there are about ten "significant impact" maritime lows.^[6]

Prior to the introduction of satellite imagery in the early 1960s, many east coast lows were classified as tropical cyclones. These storms which mostly affect the south east coast should not be confused with Australian region tropical cyclones which typically affect the northern half of the continent.^[7]

Characterisation

Explosive cyclogenesis is seen on average just once per year, but these storms cause significant wind and flood damage when they occur.^[4] Australian east coast cyclones vary in size from mesoscale (approximately 10–100 km (6–62 mi)) to synoptic scale (approximately 100–1,000 km (62–621 mi)).^[8][9]

Australian east coast cyclones, although variable in size and intensity, are typically characterised by widespread heavy rainfall.^[9] These storms usually occur along the subtropical east coast of Australia from Gladstone in Queensland to the Victoria/New South Wales border, and often affect large populated cities such as Sydney and Brisbane, between which over one-third of the Australian population resides.^[9] Rain associated damages attributed to east coast cyclones are estimated in millions to tens of million dollars annually and are a major contributor to the total weather-associated insurance losses for all of Australia.^[9] Seven per cent of all major Australian disasters since 1967 can be directly attributed to east coast cyclones.^[9] Australian east coast lows often intensify rapidly overnight making them one of the more dangerous weather systems to affect the New South Wales coast.^[6]

Pattern

The incidence of these types of storms can be seen to fluctuate quite widely from one year to the next, with none in some years and the highest incidence being twelve in 1978/79.^[7] Another feature of east coast low development is the tendency for clustering of events when conditions remain favourable. For example, near Brisbane, almost one third of events occur within 20 days of a preceding event.^[7]

Correlations of east coast cyclones with the interannual differences of the Southern Oscillation Index (SOI) indicate a strong preference for these storms to form just after a large swing from negative to positive Southern Oscillation index values and especially between swings from negative SOI the year before and positive SOI the year after. This suggests a preference for formation of east coast cyclones between extreme events of the Southern Oscillation Index.^[9]

Examples

• 5–6 June 2016^[10] An east coast low combined with a King tide brought severe coastal damage, notably to Collaroy and Coogee, New South Wales along with flooding along the east coast and later severe flooding to Tasmania.^[11]

Suomi NPP satellite image of east coast low 21 April 2015

• 2015 Australian east coast lows

• 23–25 August, An unusual low formed late in the season bringing some flooding along the coast.^[12][13] 390 millimetres (15 in) of rainfall was recorded at Nowra in 48 hours.^[14]
• 28 April–1 May^[15] – On 28 April the Bureau of Meteorology reported that an east coast low was forming off the coast of Fraser Island. Record breaking rainfall and strong winds were recorded in southeast Queensland and northern New South Wales causing 5 fatalities in the Caboolture area.^[16]
• 20–23 April^[17] At least 4 people died in an event that was described as the worst since 2007. Severe flooding affected the areas of Maitland and Dungog, inundating homes and isolating entire communities. Power and water access was restricted for tens of thousands of homes across the wider Hunter Region.^[18][19]

• 14 October 2014, New South Wales saw wind gusts up to 161 km/h (100 mph).^[20] A Bureau of Meteorology spokesman described the rainfall observed at Marrickville, Canterbury, and Sydney Airport as "probably what you'd expect to see in one location about once every 20 years", with rainfall totals in Strathfield at 94 mm (4 in) falling in just three hours described as a one in 100 years recurrence. Sydney Airport saw disruption to flights as the airport closed for a time due to high winds. In Port Botany the strong winds caused the Hapag-Lloyd cargo ship Kiel Express to break free. Waves off Sydney over 8 m (26 ft) were reported.^[21] 30,000 homes in the region were left without power.^[22]
• June 2013^[23][24]
• 21 May 2009, an east coast low caused massive coastal erosion and major flooding of the Clarence River.^[25]

Pasha Bulker stranded by an east coast cyclone on Nobbys Beach, Newcastle June 2007

• June 2007^[26] June 2007 Hunter Region and Central Coast storms the grounding of the bulk coal-carrying ship MV Pasha Bulker, ten deaths and insurance claims of around A$1.4 billion making it one of the most costly natural disasters in Australia’s history.^[3] 2007 saw five east coast cyclones develop off Australia’s east coast.^[8]
• July 2005^[27]
• March 2005^[28]
• 2 October 2004, mean wave heights off Sydney were 5m with around 10m maximum wave heights.^[29]
• 27–28 July 2001.^[29]
• 7–8 December 1998, a notorious case of explosive development in eastern Australia, the Sydney–Hobart yacht race cyclone resulted in the death of six race participants.^[5]
• 7–8 August 1998, parts of Sydney and the Illawarra region received in excess of 300 mm (12 in) of rain over four days.^[29]
• 30–31 August 1996, cost at least two lives and caused almost A$20 million in damage. Heavy rain and strong to gale force winds with extreme gusts of 64 kn (119 km/h; 74 mph) at Wollongong and 53 kn (98 km/h; 61 mph) near Sydney Airport.^[1]
• September 1995, A$8 million damage.^[1]
• August 1990, two lows in early August cause A$12 million damage.^[1]
• 5 August 1986, 24-hour rainfall totals: over 300mm in the Sydney area.^[29] Sydney's Observatory Hill recorded 327.91 mm (12.91 in) of rain, an all-time daily record for the location.^[30]
• 17–23 July 1984, A$53m insurance costs.^[8]
• 26 May 1974, storm saw the shipwreck of the MV Sygna.^[4]
• 6 July 1973, the cargo ship Cherry Venture ran aground on Teewah Beach in South East Queensland during the storm.
• June 1967, a series of east coast cyclones had a major impact on the northern New South Wales and southern Queensland coasts.^[8]
• June 1950, a series of east coast cyclones develop off the New South Wales coast during which Sydney registered its highest monthly rainfall on record, 642.7 mm (25.3 in).^[8]
• 20 August 1857, The Dunbar, a sailing ship carrying 122 people from England, was wrecked off South Head while trying to seek shelter in Sydney Harbour, leaving only one survivor.^[29]

See also

• East Australian Current
• Southerly buster
• Severe storms in Australia
• Subtropical Cyclones Australia

References

External links

• East-coast lows
• NSW Climatedogs: Eastie, East Coast Low
• ARCHIVE: Known Impacts of East Coast Lows, 1846 – 2009, detailed list of events by Jeff Callaghan for Green Cross Australia.