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Southerly is the name of a storm or front of air coming from the south. In the southern hemisphere these can be cold and have bad weather. In Wellington, New Zealand these storms are normally short and frequently have winds gusting between 120 km/h and 160 km/h though higher speeds are known. In Sydney, New South Wales, Australia these events are known as southerly busters.
On hot afternoons in the late nineteenth century, before the days of radio, the Sydney Observatory would fly a flag bearing the letters "JB" to indicate that the southerly buster had reached Jervis Bay, about 150 km to the south as the crow flies, and Henry Lawson even wrote a poem on the subject.
On sunny days in the Sydney Summer, the land heats up rapidly during the morning, while sea temperatures remain cool, typically 20 to 23 °C (68 to 73 °F). The prevailing early morning wind is a light south-west offshore breeze (a catabatic wind) that blows from land to sea, but as the land heats up a north-east convection wind develops. This is a typical "sea breeze". It starts shortly after sunrise on the coast and gradually pushes inland as the day proceeds, typically reaching the City by mid to late morning and the Western Suburbs by early to mid afternoon. Frequently, a strong offsea gale develops from the south, bringing a rapid fall in temperature, and sometimes a short, violent rain/hail storm.
Sometimes, a strong cold front approaches from the south or south-west, marking the boundary between hot and cool air masses. The temperature is dramatically dropped by a violent storm-laden southerly wind, and it is this that is known as a "southerly buster".
A more persistent and potentially violent Sydney north-easterly storm is known as a "black nor'easter". This is not a convection wind, but a storm system that develops offshore which can last several days. This is heralded by the rapid build-up of dense black cloud that can convert to a gale in well under one hour.
- Definition of southerly. The Free Dictionary. Accessed 21 February 2012.
- Southerly Busters Explained. The Australian Government Bureau of Meteorology. Accessed 21 February 2012.
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