Cyclones in Australian Region
Cyclones in the Australian region are significant weather events characterized by intense winds and heavy rainfall, primarily forming over warm ocean waters. These storms typically develop from a combination of warm sea temperatures and atmospheric wind patterns, leading to a low-pressure system that can intensify into a tropical cyclone. The cyclone season in Australia spans from November to April, with Western Australia being particularly prone to these storms. Cyclones can range in intensity from tropical storms to Category 5 systems, with the latter featuring wind speeds exceeding 252 kilometers per hour.
The impacts of cyclones can be severe, causing extensive damage to infrastructure, homes, and ecosystems due to high winds, storm surges, and prolonged rainfall. Historical events, such as Severe Tropical Cyclone Marcus in 2018 and Cyclone Yasi in 2011, highlight the potential for significant destruction and loss of life. Despite advancements in tracking and predicting cyclone paths, these storms can be unpredictable, often striking populated areas with little warning and resulting in flooding both along coastlines and further inland. Understanding the formation and potential impacts of cyclones is crucial for preparedness and disaster response in affected regions.
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Subject Terms
Cyclones in Australian Region
Tornadoes and cyclones are rotating storms that feature high winds and can potentially do a large amount of damage on land and, in particular, to population centres. Tornadoes form over hot, humid land and last only a short time. Cyclones, usually called hurricanes in the Caribbean and north Atlantic and typhoons in the north Pacific, are water-based storms formed over the ocean. The term “cyclone” is more frequently applied to the same phenomenon when the storm originates in the South Pacific or the Indian Ocean. Cyclones result from a combination of warm ocean temperatures and wind shear high in the atmosphere and, in general, do not happen year-round. Cyclone season in Australia and New Zealand is generally considered to run from November through April. Western Australia is especially subject to tropical cyclones; New Zealand is visited by both cyclones and tornadoes.
Background
The word “hurricane” comes from the Spanish huracán, originating in the Caribbean and Central America. The English word “tornado” is derived from the Spanish word tronada, which means thunderstorm. It was a nineteenth century English sailor-scientist named Henry Piddington who coined the term “cyclone” because he thought that the storm looked like the coil of a snake. The World Meteorological Organization (WMO) names significant storms. Each cyclone season begins with a storm name beginning with A; the storm names then progress alphabetically throughout the season. Some named storms are remembered long after the fact because of the damage that they caused. The WMO has, on occasion, retired a name because of the intense damage done by the storm of that name. Scientists in many countries keep track of weather systems. NASA in the United States has a network of satellites (the Geostationary Operational Environmental Satellites or GOES) dedicated to tracking storms.
Among New Zealand’s most destructive cyclones are the Great Storm of 1936; Bola, in 1988; Fergus, in 1996; Drena, in 1997; and Wilma, in 2011. Australia’s category 5 storms include Mahina, which struck Princess Charlotte Bay in 1899 and is considered Australia’s most deadly natural disaster; Innisfail, in 1918; Joan, in 1975; and George, in 2007. In 2011, Yasi, like Mahina, approached Australia from the north-east and caused $3.6 billion in damage. In 2015, Marcia also hit Queensland with winds of 300 kilometres an hour. Two years later, Cyclone Debbie hit Queensland with sustained winds of 195 km/hr. In 2023, the category 5 cyclone, Ilsa, struck Western Australia, leaving eight people dead.
Cyclones often reach peak intensity well off-shore, but destruction does not always correlate with intensity. Monica (2006), for example, is recognized as one of the most power storms recorded and made landfall in Australia twice, without loss of life or extensive property damage. Whereas, Justin (1997), a mere category 2 cyclone, killed two people in Australia and thirty in Papua New Guinea in addition to causing massive damage from rain and storm surges.
Overview
A cyclone forms as a result of a convergence of a handful of smaller storms and a large area of warm area or water. As warm air rises, it takes pressure with it, leaving behind an area of lower air pressure near the surface. This is not a cut-and-dried process, and a pocket of rising air often creates a wall of air and water that then forms into a large storm that spins inward towards an area of low atmospheric pressure. More warm air rising means more air swirling around the low pressure area; the rising air, meanwhile, cools off and the water in the air forms clouds that then carry rain. All of this together can pack a powerful punch as it becomes mobile.
The higher a storm’s wind speed, the higher its intensity. A storm with a wind speed of 63–118 kilometres per hour is classified as a tropical storm. Once a storm reaches a wind speed of 119 kilometres per hour, it is called a tropical cyclone. The higher the intensity, the higher the number on the Saffir-Simpson Hurricane Wind Scale, which runs 1 to 5:
Category 1: 119-–153 km/h
Category 2: 154–177 km/h
Category 3: 178–208 km/h
Category 4: 209–251 km/h
Category 5: 252+ km/h
The eye is the centre of the storm. Because of the Coriolis Effect (a system of deflection based on the earth’s rotation), cyclones in the Southern Hemisphere spin clockwise, the opposite of their Northern Hemisphere counterparts. This deflection also is what keeps the storm’s eye calm: the rotation deflects the pressure of the strongest winds away from the eye.
Cyclones are very large storms. An average hurricane has a diameter of 161 kilometres. The largest Atlantic hurricane ever recorded had a diameter of more than 2,400 kilometres. It is not just the size of a storm that makes one deadly, however. Strong winds and inundation by rain and storm surges batter homes and other buildings, undermine infrastructure such as roads and communication lines, strip and topple trees, and kill exposed livestock.
As their name suggests, tropical cyclones form in the tropics, between 5 and 30 degrees latitude on either side of the equator, because these storm systems need warm ocean air and water in order to form and intensify. As a hurricane approaches land, the storm’s winds increase the size of the waves and draw more heat and moisture into the storm, giving it even more strength. Rising waves result in storm surges that drive far up beaches and force water back up rivers. Mahina’s surge was almost 13 metres. Most deaths caused by cyclones occur from storm surges.
Cyclones can be tracked and their path projected, but they remain unpredictable. They can hit population centres with dizzying speed and power. Further, large storms can stall over land as they lose intensity; however, the drop in momentum does not also mean a lessening of the sheer amount of water in the storm system — torrential rains may fall on the same spot for days. Thus, it is possible for cyclones to cause widespread flooding both in coastal areas and further inland.
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