A southerly buster is the colloquial name1850, B. C. Peck, Recollections of Sydney, quoted in 1978, G. A. Wilkes, A Dictionary of Australian Colloquialisms, of an abrupt southerly wind change in the southern regions of New South Wales and Victoria, Australia, which approaches from the southeast, mainly on a hot day, bringing in cool, usually severe weather and a dramatic temperature drop, thus ultimately replacing and relieving the prior hot conditions.
Marking the boundary between hot and cool air masses, a southerly buster is sometimes represented by a roll cloud perpendicular to the coast, which appears from the south and coexists with the wind change, though sometimes there is little visual signal of the southerly's arrival.Southerly Busters Explained. The Australian Government Bureau of Meteorology. Accessed 21 February 2012. Southerly busters occur in the backside of a low pressure trough in the Tasman Sea, followed by the speedy advance of an anticyclone south of Western Australia and South Australia (around the Great Australian Bight). They are caused by the interaction of a shallow cold front with the blocking mountain range that aligns the coast, and frictional contrasts over the mainland and the ocean that disconnect the flow.
Southerly busters occur about 32 times each year on the coast of southeastern Australia, with variable strength, usually in spring and summer. Although southerly busters are often associated with NSW and Victoria, they also occur on the east coast of Tasmania, New Zealand, and in Argentina and Chile.Cassiily, M. 1945. The frontology of sub-tropical Australia. RAAF Met. Services Weather Development and Res. Bulletin. 1. 5–28. The name 'southerly buster' initiated as a slang term used by Sydneysiders, though it has since evolved into an official weather attribute in the Bureau of Meteorology terminology. Global warming has decreased their frequency, with falls of in minutes being less recorded, where they can disrupt flights, create dangerous sea conditions, and intensify bushfire danger.
History 19th century
In 1819, Australian explorer William Wentworth describes the southerly buster experienced in Sydney:
...They [hot northwesterly winds] seldom, however, continue for more than two days at a time, and are always superseded by a cold southerly gale, generally accompanied with rain. The thermometer then sinks sometimes as low as , and a variation of temperature of from 30 to 40°F (about 17 to 22°C) takes place in half an hour. These southerly gales usually last at this season from twelve to twenty-four hours, and then give way to the regular sea and land breezes...Statistical, Historical, and Political Description of NSW by William Charles Wentworth, 1819
From the early days of settlement at Sydney Cove, sudden southerly squalls had been a problem for boats in the harbour. In 1829, a brickfielder as these squalls as were then called, laid the boat carrying Governor Ralph Darling and his family on its beam ends. Later Port Jackson boatmen would call it, the "Sútherly Búster".Mundy, Godfrey Charles. Our Antipodes, or, Residence and Rambles in the Australasian Colonies : with a Glimpse of the Gold Fields / by Godfrey Charles Mundy. Richard Bentley, 1852. page 83 During the early days of the European settlement, Sydney's summer storms were accompanied by rolling red dust from the colony's brickworks.Arthur Phillip Chapter of Fellowship of First Fleeters – WEATHER SECRETS OF THE FIRST FLEET VOYAGE
In 1869, following the connection of lighthouses and signal stations on the east coast of NSW to the electric telegraph network, a system was instituted to give shipping warning of approaching gales. It would give boats in Port Jackson warning of approaching busters. The new signals were included in Gowland's amendments to the NSW Sailing DirectoryAdditions and Corrections to the present Admiralty Sailing Directory for the Coast of New South Wales, Navigating Lieut. J.T.Gowlland R.N., Sydney, Thomas Richards Govt. Printer 1870 The signal was a diamond shape (see Day shapes) on the southern yard-arm of the signal mast to indicate a squall approaching from the south, and numeral pendants per John Nicholson's Code of Signals flying on the masthead to show the location of the squall. The numbers were those already in use from 1842 for identifying ports, e.g. Jervis Bay was 46 and Wollongong, added in 1854, was 82. The signal masts were at South Head Signal Station and Fort Phillip. These masts had two yard-arms at right angles aligned north–south and east–west. The success of the system was seen in 1870 when a newspaper reported, "About 9 o'clock, however, intelligence of a southerly burster was telegraphed from Eden, and by half-past 12 the expected 'brickfielder' blew over the city."Evening News (Sydney, NSW : 1869 - 1931), Friday 14 January 1870, page 2, The Weather
From 1876 signals would be displayed at two additional places - the new flagstaff at Bradley's Head and the Floating Light Vessel at the entrance to the harbour. This direction specified that a cone signal on the flagstaff would indicate the approach of a southerly squall. This signal, "A cone, with the point downwards, shows that a gale is probable; at first from the southward.",The Weather Book : A Manual of Practical Meteorology, Rear Admiral FITZROY. - London : Longman, Green, Longman, Roberts, & Green. 1 8 6 3.- p. 347 was introduced in England 1861Jim Burton. “Robert FitzRoy and the Early History of the Meteorological Office.” The British Journal for the History of Science, vol. 19, no. 2, 1986, p 161. JSTOR, www.jstor.org/stable/4026590. Accessed 11 June 2020 by Robert Fitzroy, but this appears to be the first time it was used in Port Jackson. In 1879, George Herbert Gibson published a book called Southerly Busters, where a buster wreaks havoc near Hyde Park, Sydney.
In November 1898, the Postmaster General, Varney Parkes, announced that a white flag with the letters E, J.B. or W would be flown from the flagstaff on the clock tower of the General Post Office, Sydney to signal the approach of a southerly buster. As the wind reached Eden, Jervis Bay or Wollongong the relevant flag would be hoisted. The J.B. flag was hoisted for the first time on 10 February 1899 but the wind did not travel beyond Kiama. The day had been hot and oppressive and the much anticipated cool change did not eventuate. The original intention was to change the flags as the change moved north but this did not always happen. It was possibly later reduced to just two flags, JB and W.H.O Publication No. 169, Australia Pilot, Volume III, 2nd Edition 1930, United States Govt Printing Office
20th century
On the night of 16 December 1908 a new signal, also on the GPO clock tower, made its debut. For warnings at night a red light had been installed in the lantern - the glass enclosed room below the flagstaff. It continued until 1940. Capsizes still occurred, but fishing boats did heed the warnings.
In 1931, with the addition of signals for southerly busters, the practice of displaying the Bureau of Meteorology weather forecast with flags was extended, with the cooperation of the Royal Australian Navy, to the signal staff on Garden Island. The weather flags had been flown since 1912 from the flagstaffs on prominent buildings but as well, at Garden Island, a diamond shape would be hoisted for warnings during the day and a red light at night when a southerly buster was expected. In 1932 Navy League sea cadets flew the same signals as at Garden Island at their station on Snapper Island (New South Wales).
The Weather beacon on the top of MLC Building, North Sydney, built in 1957, could also warn of 'southerly busters'. Generally, the forecasts displayed by the lights were updated three times a day but could be changed at anytime if a sudden change was imminent. If a 'buster' was expected the red lights at the bottom of the beacon would flash at half second intervals., This signal, indicating strong winds and rain, was not specific to 'southerly busters', but as the jingle advised:
Flashes short, prepare for gales, Gather the washing, furl the sails."
Author Ruth Park makes a reference to the southerly buster in her novel Poor Man's Orange (1949):
After an unbearably hot day, the old men on the balconies were sniffing the air and saying, 'Here she comes!' The Southerly Buster, the genie of Sydney, flapped its coarse wing over the city ... The women undid the fronts of their frocks and the little children lifted up their shirts and let it blow on their sweaty bottoms.
Analysing statistics from 1970 to 2023 determined that that prior to 1995, southerly busters were predominantly severe and were determined by wind gusts greater than . After 1996, the number of less severe busters started to increase, and these milder southerly busters increased significantly between 2017 and 2022 – There was a large increase in weaker southerly busters over the triple La Niña years of 2020 to 2022, which were usually unnoticeable due to their lack of gusts.
Formation
Southerly busters generally develop when a shallow front of cold air arises against the Great Dividing Range. Due to "the orientation of the topography, it slows down over the land because of friction and then it pushes up the coast because it gets trapped", according to Dr Milton Speer, a visiting scholar at the University of Technology Sydney. They mostly form on a hot day, arriving as a strong offshore gale (from the south) that reach the land in the late afternoon, causing a rapid fall in temperature. Sometimes, due to the blocking mountain range paralleling the coast and frictional disparities over land and the ocean which disconnect the flow, a short rain and/or severe thunderstorm activity may accompany, especially if it is affiliated with a cold front coming from the south and a trough.
Other phenomena can lead to amplification of the temperature gradient between the warm air mass and the cold density current, such as hot north-westerlies or a foehn wind that antedate the squall. The southerly buster, which usually trails a thick layer of low stratus clouds bringing episodic drizzle, banks up against the Great Dividing Range, thus resulting in the transmission of the cool maritime air near the southeastern part of the ranges and the blocking of the airflow on the mountains' west side. The Buster progresses into a strongly stable boundary layer with warm, prefrontal landmass air that is between 100 and 200 metres deep transporting over the cooler waters.Shallow Cold Fronts - Cloud Structure In Satellite Images by EUMeTrainReid, H.J. 2000, "Regeneration of the Southerly Buster of Southeast Australia". Weather and Forecasting Vol.15, pp432-446
In some occasions, a cold front in the Southern Ocean may interact with the Great Dividing Range and develop into a Southerly Buster. It is worth noting that some Southerly Busters are not southern ocean fronts, as they have developed on the pre-frontal trough south of Australia or have possibly originated on the southern NSW coast in affiliation with a shallow mesoscale low development. As the Southerly Buster advances to the north, its force would decrease, though in rare occasions it can fortify north of the Hunter Valley due to upslope motion on the valley's north, which allows the flow to produce anticyclonic vorticity akin to the original obstruction and arrangement of the Southerly Buster in Victoria.McInnes K. L., 1993: Australian southerly busters. Part III: The physical mechanism and synoptic conditions contributing to development. Mon. Wea. Rev., 121, 3261 - 3281