Many homes and businesses have been damaged after Tropical Storm Mangga swept into the coast of Western Australia early on the morning of Monday 25 May 2020, bringing with it windspeeds of up to 132 km per hour. There are no reports of any casualties at the time of writing, but about 62 000 people are thought to have been left without power across the state, and there are widespread reports of trees being knocked over, damage to roofs and coastal defences, with at least one ship reported to have shed some of its cargo off the coast. The storm is also reported to have triggered dust storms in part's of the state's interior.
Damage to shopfronts in Perth, Western Australia, caused by Tropical Storm Mangga. Richard Wainwright/EPA.
Tropical storms, called Cyclones in the Indian Ocean and South Pacific, are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.
Damage to a home in the Geraldton suburb of Waggrakine, caused by Tropical Storm Mangga. City Of Greater Geraldton.
Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.
Damage to coastal defences at Port Beach, Western Australia, caused by Tropical Storm Mangga. Nicolas Perpitch/ABC News.
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