Cyclone Freddy made landfall in the coastal town of Vilanculos in southern Mozambique on Friday 24 February 2023, brining with it windspeeds of 113 km per hour, as well as high rainfall levels. The rain is predicted to be the bigger part of the problem for the country, which is already suffering from widespread flooding following exceptionally high seasonal rains, and may also cause problems in neighbouring Malawi, Zimbabwe, and northern South Africa. While the storm is likely to bring severe problems to the country, it is hoped that the number of casualties will be kept low, with thousands of people having been evacuated from the path of the cyclone as part of the World Meteorological Organization's Early Warnings for All Programme. The storm has already claimed seven lives in Madagascar, as well as causing damage to property on the islands of Mauritius and La Reunion.
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..
Cyclone Freddy is particularly unusual in that it formed off the coast of Australia, tracking its way across the entire southern Indian Ocean before hitting Madagascar and Mozambique. It is only the fourth time a storm has been recorded doing this, with the previous examples being cyclones Litanne in 1994 and Leon–Eline and Hudah in 2000. This long journey allowed Freddy to gain considerable energy, hitting Madagascar as a Category 5 Cyclone (i.e. a storm with sustained winds in excess of 252 km per hour). The storm lost most of its energy passing over the island, but regained some of this passing over the Mozambique Channel.
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.
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