Australian east coast lows (known locally as east coast lows, maritime lows, and east coast cyclones [1] ) are extratropical cyclones or low-pressure systems on the coast of southeastern Australia that may be caused by both mid-latitude and tropical influences over a variety of levels in the atmosphere. [2] [3] These storms should not be confused with Australian region tropical cyclones which typically affect the northern half of the continent. [4]
The most intense of these systems have many of the characteristics of subtropical cyclones. [5] They develop between 25˚ south and 40˚ south and within 5˚ of the eastern Australian coastline, [1] mostly during autumn and early winter with a peak in June. [6] [7] [8] Prior to the introduction of satellite imagery in the early 1960s, many east coast lows were classified as tropical cyclones. ECLs are responsible for more than half of all days with rainfall above 50 mm (2.0 in) in the southeastern seaboard. [9]
Generally, the low occurs when there exists a temperature contrast between the warmer Tasman Sea and cooler continental landmass (including the cold air in the upper atmosphere). The interaction of such airs create heavy moisture and heightened wind speed. [10] Two thirds of the recorded low-pressure systems are fully cold core storms while the remaining third display hybrid features, which are defined by a warm core at lower levels and a cold core at upper levels. A smaller portion are fully warm core cyclones, where they somehow transition to a tropical cyclone, as well as in part warm seclusion cyclones. Furthermore, 46% of ECLs were hybrid cyclones. [11]
An east coast low can develop in a variety of other weather conditions, including:
Explosive cyclogenesis is seen on average just once per year, but these storms cause significant wind and flood damage when they occur. [7] East Coast Lows by and large have shorter lifespans than Tropical Cyclones, lasting only a few days. [12] Australian east coast cyclones vary in size from mesoscale, around 10–100 km (6–62 mi), to synoptic scale, approximately 100–1,000 km (62–621 mi). [14] [15] Cold core cyclones are more predominant in the southern parts of the ECL region during the cool season, while hybrid cyclones are more regular closer to the tropics, particularly in the warm season. [11]
Australian east coast cyclones, although variable in size and intensity, are typically characterised by widespread heavy rainfall. [15] 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. [15] Seven per cent of all major Australian disasters since 1967 can be directly attributed to east coast cyclones. [15]
ECLs are the cause of more than 25% of yearly rainfall and more than 60% of days with mass coastal flooding or significant dam influxes. [9] A Tasman Low is an offshore low that occurs around 200 km away from the coast which can cause light to moderate rainfall and gusty winds, although its effect is insignificant compared to that of an east coast low. [10]
East coast lows usually occur along the subtropical east coast of Australia from Gladstone in Queensland to the Victoria/New South Wales border in the South Coast (near eastern Gippsland), and often affect large populated cities such as Sydney and Brisbane, between which over one-third of the Australian population resides. [15] ECLs are generally more intense between Batemans Bay in the south to Coffs Harbour in the north, which include the Mid North Coast, Central Coast, Hunter Valley, Sydney CBD, the Illawarra, and as well as the Blue Mountains and Southern Highlands. South East Queensland, the far southern coast and Northern Rivers of New South Wales, and eastern Victoria are generally less impacted than the areas situated at the centre of the NSW coastline. [16]
More powerful systems may percolate inland into the Central Tablelands, New England, the Central West, South Western Slopes, the Monaro and, albeit rarely, the Orana and the Riverina regions in NSW; also the Australian Capital Territory, the Hume region in Victoria; as well as Darling Downs and the Brigalow Belt in Queensland, although the rainfall in these interior areas will often be insignificant. [9]
In a June 2007 observation by the Bureau of Meteorology, there were about ten significant maritime lows with an "explosive development" usually occurring once per year. [12] Much recently, it was observed that around 22 east coast lows were recorded annually – around 2 to 3 causing daily rainfall above 100 mm (3.9 in) and 7–8 causing daily rain above 25 mm (0.98 in). [3] A Black nor'easter, which occurs in the warm months in eastern New South Wales, can intensify as it heads south and turn into an east coast low. [17]
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. [4] 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. [4] Areas south of the low can experience heavy rain, while those at the north of the rotating low would experience sunny skies. The movement of the low pressure system is generally difficult to predict for weather forecasters. [12]
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. [15] A positive SAM is linked with a higher frequency of deep cyclones in August–October and of shallow upper cyclones in December–February. [9]
Severe storms in Australia refers to the storms, including cyclones, which have caused severe damage in Australia.
The climate of Sydney, Australia is humid subtropical, shifting from mild and cool in winter to warm and occasionally hot in the summer, with no extreme seasonal differences as the weather is moderated by proximity to the ocean, although more contrasting temperatures are recorded in the inland western suburbs. Despite the fact that there is no distinct dry or wet season, rainfall peaks during summer and autumn months, and is at its lowest just around the middle of the year, though precipitation can be erratic throughout the year. Precipitation varies across the region, with areas adjacent to the coast being the wettest. According to the Bureau of Meteorology, Sydney falls in the temperate climate zone which has warm to hot summers and no dry season. Sydney's plant hardiness zone ranges from zone 11a to 9b throughout the metropolitan area. Under the Holdridge Life Zones classification, eastern Sydney falls in the Subtropical Moist Forest zone and the western suburbs in the Subtropical Dry Forest zone.
Drought in Australia is defined by the Australian Bureau of Meteorology as rainfall over period greater than three-months being in the lowest decile of what has been recorded for that region in the past. This definition takes into account that drought is a relative term and rainfall deficiencies need to be compared to typical rainfall patterns including seasonal variations. Specifically, drought in Australia is defined in relation to a rainfall deficiency of pastoral leases and is determined by decile analysis applied to a certain area. Note that this definition uses rainfall only because long-term records are widely available across most of Australia. However, it does not take into account other variables that might be important for establishing surface water balance, such as evaporation and condensation.
The 2002–03 Australian region cyclone season included Cyclone Inigo, which tied with Cyclone Gwenda in 1999 as the most intense tropical cyclone on record in the Australian basin. It began on 1 November 2002 and ended on 30 April 2003. The regional tropical cyclone operational plan also defines a tropical cyclone year separately from a tropical cyclone season, which runs from 1 July 2002 to 30 June 2003. These dates conventionally delimit the period of each year when most tropical cyclones form in the Australian region, which is defined as in the southern hemisphere between 90°E and 180°E. The season's ten tropical depressions existed within these dates, with the first, designated as Tropical Cyclone 07S, entering the basin on 27 December 2002. The last system, Cyclone Epi, dissipated on 6 June 2003. Tropical cyclones in this area were monitored by four Tropical Cyclone Warning Centres (TCWCs): the Australian Bureau of Meteorology (BOM) in Perth, Darwin, and Brisbane and one in Port Moresby, Papua New Guinea.
The 1950 rainfall records for the Australian states of New South Wales and Queensland reported probably the most remarkable record high rainfall totals ever recorded anywhere in the continent. Averaged over both of these states, 1950 is clearly the wettest year since adequate records became available circa 1885. Queensland recorded a statewide average rainfall of around 1,125 millimetres (44.3 in) as against a mean since 1885 of around 640 millimetres (25.2 in), whilst New South Wales recorded around 930 millimetres (36.6 in) as against an instrumental mean around 520 millimetres (20.5 in). Australia's wettest town, Tully also recorded its highest annual rainfall total in 1950 with 7,925 millimetres (312.0 in).
Severe Tropical Cyclone Aivu was a powerful late-season tropical cyclone that caused extensive damage across parts of Queensland, Australia in April 1989.
Australian rivers have been subject to devastating floods in New South Wales, recorded since colonisation. Flooding in New South Wales has predominately been caused by excessive flows into rivers located in New South Wales and, to a lesser extent, excessive flows into rivers located in Queensland and Victoria. Floods can devastate local communities and impact the entire local economy.
Severe Tropical Cyclone Yasi was a powerful and destructive tropical cyclone that made landfall in northern Queensland, Australia in early 2011, causing major damage to the affected areas. Originating as a tropical low near Fiji on 26 January, the system intensified to tropical cyclone status during the evening of 30 January. Yasi deepened rapidly over the next 24 hours, and was classified as a Category 3 cyclone at about 5 PM AEST on 31 January 2011. Late on 1 February, the cyclone strengthened to a Category 4 system; then, early on 2 February, the cyclone intensified into a Category 5 Severe Tropical Cyclone. The system had a well-defined eye and continued to track west-southwestward, maintaining a central pressure of 930 hPa and a Dvorak intensity of T6.5 into the evening.
Severe Tropical Cyclone Jasmine was a powerful and long-lived annular tropical cyclone that affected several countries, particularly Vanuatu and Tonga, over a 16-day span in February 2012. The system was the second cyclone and the only severe tropical cyclone of the relatively quiet 2011–12 South Pacific cyclone season. Cyclone Jasmine developed from an area of disturbed weather on 1 February in the Gulf of Carpentaria. Initially, the storm moved towards the east and across the Cape York Peninsula. As it moved across the South Pacific, earlier existing wind shear conditions lessened, and Jasmine began to strengthen at a faster rate. Steadily intensifying, Jasmine reached peak intensity on 8 February as a Category 4 equivalent on the Saffir–Simpson Hurricane Scale, while beginning to show annular characteristics.
Tropical Cyclone Oswald in 2013 was a tropical cyclone that passed over parts of Queensland and New South Wales, Australia over a number of days, causing widespread impact including severe storms, flooding, and water spouts. Coastal regions of Queensland were the most impacted with Mundubbera, Eidsvold, Gayndah and Bundaberg in the Wide Bay–Burnett hit severely. In many places the rainfall total for January set new records. Across the affected region, damage from severe weather and flooding amounted to at least A$2.4 billion.
Severe Tropical Cyclone Christine was the third tropical cyclone and the second severe tropical cyclone of the 2013–14 Australian region cyclone season. It made landfall on Western Australia's Pilbara coast nearly halfway between the major towns of Karratha and Port Hedland as a category 4 cyclone on midnight of 31 December 2013.
Severe Tropical Cyclone Debbie in 2017 was the strongest tropical cyclone to strike Queensland since Marcia in 2015, and was the costliest tropical cyclone in Australia since Yasi in 2011. Forming as a tropical low on 23 March, the low gradually intensified into a named tropical cyclone on 25 March. After steadily strengthening offshore to a Category 4 system, Debbie eventually made landfall near Airlie Beach, at 12:40 AEST on 28 March. Afterwards, Debbie rapidly weakened into a tropical low by late 28 March, but continued to travel south, causing significant damage and flooding in the populous areas of South East Queensland and Northern Rivers. In total, the storm caused A$3.5 billion (US$2.67 billion) in damage and fourteen deaths across Australia, primarily as a result of extreme flooding. This makes Debbie the deadliest cyclone to hit Australia since Fifi in 1991.
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Severe weather events or extreme weather events in Sydney, Australia, include hailstorms, thunderstorms, gale, bushfires, heatwaves, drought, and flash flooding from heavy rain. Sydney is rarely affected by cyclones, although remnants of cyclones do affect the city.
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Severe Tropical Cyclone Dinah was an intense tropical cyclone that impacted the southern coasts of Queensland and New South Wales, causing floods and landslides in 1967. It was regarded by an official in the Bureau of Meteorology's Brisbane Tropical Cyclone Warning Centre as the strongest storm to approach the southern coasts of Queensland since reliable records began. Forming on January 22 in the South Pacific basin, nearly 620 kilometers to the southeast of Honiara in the Solomon Islands, the disturbance that would eventually be Dinah remained disorganized until the next day when the system started to organize under the warm waters of the Coral Sea. On January 24, the disturbance was upgraded to a tropical cyclone by the BoM and was named Dinah, being the fifth storm in the records of the meteorology center of Australia in the 1966–67 Australian region cyclone season. Environmental conditions favoured Dinah to further intensify, becoming a severe tropical cyclone on January 27 while recurving south-southwestwards. On the next day, it passed through the Great Barrier Reef as a Category 4 severe tropical cyclone before passing through Fraser Island on January 29, where the Sandy Cape Lighthouse recorded a minimum barometric pressure of 944.8 hPa on Dinah, being the lowest known pressure of the system. It then battered the whole island before turning south-southeastwards, away from the coast of Queensland. Weakening took place while slowing down, passing near Lord Howe Island as a Category 2 tropical cyclone before undergoing extratropical transition on January 31. Dinah became extratropical on the night of that day before accelerating eastward, approaching New Zealand. The system then turned southeastward for the final time before passing through the North Island. It reemerged on the Southern Pacific Ocean on February 3, where it dissipated.
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2022 was an extremely wet year for Australia, coming out of a back-to-back La Niña in the summer of 2021-22, a Negative Indian Ocean Dipole developing over the winter and a third back-to-back La Niña in the spring of 2022.
Tropical Cyclone Seth was a strong tropical cyclone whose main impacts came after it degenerated into a remnant low. The eighth tropical low and the fourth tropical cyclone of the 2021–22 Australian region cyclone season, Seth originated from a tropical disturbance in the Timor Sea and caused severe flooding in southeast Queensland and hazardous surf along the southeastern coast of Australia.