A tropical cyclone is a rotating weather system with a middle lower than 1000hPa, this isolated circulation is characterised by powerful winds and its unique make-up of thunderstorms which cause heavy rain. Storms are named differently according to geographical location (typhoon, hurricane, tropical cyclone), but all consist of the same properties, with only the direction of rotation a movement differing between hemispheres. Continuing along the lines of geographical naming, the official name 'tropical cyclone' is derived from its formation in areas considered to have tropical weather patterns. The term 'cyclone' is derived from the cyclonic movement caused by the Coriolis force, due to this tropical cyclones generally do not form within 5° longitude of the equator. Cyclones are fed by evaporating water, therefore require water to form and sustain development.
Required Conditions
The conditions required for a cyclone to develop are categorized by 6 main points. Warm water is paramount for a tropical cyclone to begin formation water temperatures need to be upwards of 26.5°C over an extended period allowing sufficient evaporation to take place. Unstable upper air conditions can sometimes lead to cyclogenesis at lower water temperatures due to a change in dry and wet lapse rates which differ according to atmospheric pressure, these instabilities can be caused by differing wind patterns illustrated by. Upper atmospheric moisture also plays a part during cyclogenesis as temperatures can fall as low as -30°, this can result in convection and condensation in even the very dry atmospheric conditions. The Coriolis force must be present for cyclogenesis to begin, the low-pressure centre is required to be about 500km from the equator in order for the pressure gradient to begin creating winds that blow in a circular motion due to the Coriolis force. A low-level disturbance is imperative as even with perfect upper air conditions cyclogenesis can not happen without the correct surface focus. Vertical wind shear of less than 10m/s^(-1) aids the development of the tropical cyclone, higher vertical shear wind speeds can rip the cyclone apart before it can fully form. If all 6 of these points fall in line the likelihood of the formation of a tropical cyclone forming is high, also take into account that not all factors must be present and sometimes cyclones can form in unlikely conditions.
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Stages of Development
The development and decline of a tropical cyclone are characterised by four main stages: the formative, immature, mature, and decaying or degenerative stages. Each stage has a specific name, whereas only the third stage is named a tropical cyclone. In the first stage, the formative stage (tropical depression), atmospheric pressure begins to decrease but is still above 1000hPa, winds circulate around the developing low pressure, winds can reach 64km/h, and large spirals of cumulonimbus clouds form around the centre. In the second stage, the immature stage (tropical storm), pressure must fall below 1000hPa in the centre of the storm, isobars for a more circular shape, an eye and eyewall begin to form a defining centre, wind speed is between 65km/h and 117km/h and are fastest near to the eye, the storm also contains an active quadrant. In the third stage, the mature stage (tropical cyclone, pressure in the eye dips below 980hPa and remains constant, wind speed is now at a minimum of 118km/h, cumulonimbus clouds for a clear eye and eyewall visibly show the eye. And in the fourth stage, the degenerating stage, pressure begins to increase again, the size and area covered begin to decrease, wind speed begins to fall, and heavy rain still falls, but the tight wall of cloud begins to break apart. A tropical cyclone can dissipate at any stage if one of the required development criteria is lost, this can be caused by the storm's location or it is passing over land among other reasons. Tropical cyclones that have reached the fourth stage are able to regenerate if the necessary conditions are reintroduced to the storm. The regeneration of a tropical cyclone in the fourth stage leads to it regaining tropical cyclone status.
Impact of Settlements
Tropical cyclones' strength of rain and wind makes them a serious danger to human settlements. Countries like Madagascar and Mozambique are lashed by tropical cyclones every year and require large amounts of money to deal with this fact. The high wind that accompanies tropical cyclones is dangerous for underdeveloped countries as infrastructure is not built strongly enough to withstand the extreme force imparted on it by the wind. Countries like Mozambique, which lack the resources to reinforce against tropical cyclones, run the risk of getting into an endless cycle of repairing and having buildings, businesses and homes destroyed. However, not only the east coast of Africa is battered every year, but also the east coast of the United States, the west coast of Australia, and western Southeast Asia. These more developed countries lose more money to tropical cyclones every year than the African countries, but have a much faster recovery time, leading to less hampering of development. Displacement of people out of areas that are badly affected by tropical cyclones is less prevalent. For example, Madagascar is more developed on the eastern side of the nation, which is more heavily affected than the west side. In general, people’s settlement has adapted to deal with the threat of tropical cyclones, which provides some protection against the threat, but many lives are still lost each year, between drownings, disease outbreaks, infrastructure failures, and lack of attention to injuries sustained during cyclonic events. Tropical cyclones have caused an estimated 1.33 million deaths since the start of the 20th century and affected more than 629 million people in this time.
Strategies for Dealing with Cyclones
The severity of tropical cyclones means that strategies for dealing with them become more important every year, strategies that can save lives as well as costs. Some of these strategies are easily implemented by private individuals, while others are nationwide initiatives orchestrated by governments. These strategies are the adaption that was previously mentioned, preventing displacement of people. Household strategies are employed by people to reduce damage and danger levels to the lowest level possible. The following are some important ones: cut and prune all trees on your property year-round; have a designated location for loose items that lie around your house (preferably a sheltered area); protect and reinforce windows and doors with plywood; devise an evacuation plan. In less developed countries, the aforementioned may be adapted to suit the different socio-economic environments and local conventions. The governmental level of preparedness and strategies for dealing with tropical cyclones is on a very large scale and in some cases can cost millions of dollars. There are often 'acts' implemented by governments in order to help deal with the dangers of tropical cyclones, these acts often set aside money in annual budgets to help with tropical cyclone relief and post-cyclone rebuilding. Governments will often end up needing to appeal for foreign aid when faced with extreme cyclonic events. Issues in terms of preparedness usually arise when a country is in a weakened economic state or when storms do not follow predicted paths and impact an area unexpectedly. Without the aforementioned strategies, dealing with tropical cyclones would be exponentially more difficult, leading to the eventual economic decline of a country.
Conclusion
With the facts listed throughout this essay, it is clear the severity of tropical cyclones and showing easily why they are one of the deadliest natural disasters and extreme weather events which can occur. Their close monitoring and prediction are massively important, and it is also of the utmost importance that in the event of a tropical cyclone the people of a nation are provided with the support they require.
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