Tropical Cyclones: Their Formation and Impact

Our planet has been facing a higher frequency of extreme weather patterns and events. Natural disasters such as earthquakes, volcanic eruptions, hurricanes, tsunamis, and flooding have resulted in great loss of human life as well as the destruction of homes and other property, infrastructure, and livelihoods. Many people live in natural disaster-prone areas such as Indonesia, which has experienced devastating floods, earthquakes, and tsunamis in the last year alone. The recent Cyclone Idai has also resulted in unforeseen losses in Southern Africa. Understanding cyclone formation is at the center of providing early warnings that enable much-needed disaster preparedness.



The Formation of Cyclones, Hurricanes, and Tsunamis

Although they go by different names, cyclones, hurricanes, and tsunamis are effectively the same creature. The difference is the region where these occur. When this weather phenomenon occurs in the Atlantic and Northeast Pacific, it is referred to as a hurricane. In the Northwest Pacific, it is a typhoon, and in the South Pacific and the Indian Ocean, it is a cyclone.

The generic term used for all three occurrences is a tropical cyclone. A tropical cyclone begins when clouds and thunderstorms in an organized, rotating system form over tropical or subtropical waters. The circulation must be closed and low-level. Rotation is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

When the maximum sustained winds are at most 38 miles per hour (mph) or 33 knots, the phenomenon is classed as a tropical depression. In the range of 39 to 73 mph, the term tropical storm is used. The classification as a hurricane, cyclone, or typhoon happens when there are maximum sustained winds of at least 74 mph. When the maximum sustained winds reach at least 111 mph, then it becomes a major hurricane. These are classified on the Saffir-Simpson Hurricane Wind Scale as either Category 3, 4 or 5.

A Look at Cyclone Idai

Cyclone Idai occurred between March 4th and 21st 2019. Behind the 1892 Mauritius cyclone, it is the second-deadliest tropical cyclone to be recorded in the South-West Indian Ocean. Looking at the entire Southern Hemisphere, it ranks third-deadliest.

Monitoring of the cyclone began on March 1st, 2019 when the French national meteorological service office in Reunion began tracking prolonged circulation. As the system continued to gain in strength, it moved across Africa’s east coast. It hit land in Mozambique as Tropical Depression 11, redirected, and re-emerged a few days later as a Category 1 hurricane on the Saffir-Simpson scale. Cyclone Idai moved on to impact, not just Mozambique and Madagascar but also land-locked Malawi and Zimbabwe. At its peak, it reached wind speeds of 125 mph, the equivalent of a Category 3 hurricane.

As Cyclone Idai moved inland, it brought with it heavy rains, flash floods, mudslides in the mountainous areas, widespread flooding, and extreme winds. In terms of impact, there have been at least 1,000 fatalities, over 2,000 missing, and over 2,000 injured. Millions have also been affected and displaced, and the monetary damage is estimated to be over US$1 billion.

Early Warnings and Disaster Preparedness

Weather stations globally play an important role in tracking the early signs of potential extreme weather and natural disasters. They give governments and communities the early warnings they need to prepare for impending disasters. Depending on the nature of the disaster, people may need to be evacuated, taken to higher or safer ground, and equipped with food and water supplies should they be later cut off. In lower-income areas, there are still challenges and inefficiencies in how this is done. Finally, in the aftermath of a natural disaster, there comes the combined effort of providing relief in different forms and assessing the impact.

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