Angola's Hurricane History: A Calm Coast?

Angola is located in Southern Africa, a region that is generally safe from tropical cyclones. This is due to the lack of the Coriolis effect near the equator, which is essential for the spin that gives rise to low-pressure systems. However, in rare cases, tropical cyclones have been known to traverse southern Africa, such as Cyclone Bonita in 1996, which moved from the South-West Indian Ocean to the South Atlantic. In addition, global warming is causing an increase in the frequency and intensity of storms in Africa, exacerbating socioeconomic stressors across the continent.

Angola's location in the Southern Hemisphere means tropical cyclones are extremely rare

Angola is located on the west coast of Southern Africa. While Africa is bordered by several cyclone-producing tropical ocean basins, Angola's location in the Southern Hemisphere means tropical cyclones are extremely rare.

The only basin that regularly produces tropical storms or hurricanes that affect Africa is the southwest Indian Ocean. However, even this basin rarely affects Angola, as storms typically move westward or southwestward toward Madagascar or Mozambique.

In addition, the formation of tropical cyclones in the Southern Hemisphere is hindered by strong wind shear, which disrupts the formation of cyclones, as well as a lack of weather disturbances favourable for their development in the South Atlantic Ocean. As a result, Hurricane Catarina in 2004 is the only recorded South Atlantic hurricane in history.

While Angola is generally safe from tropical cyclones, it has experienced at least one tropical storm. In April 1991, a low-pressure area formed over the Congo Basin and moved offshore northern Angola. According to the United States National Hurricane Center, the system was likely either a tropical depression or a tropical storm at its peak intensity. This is the only recorded tropical cyclone in the eastern South Atlantic.

Furthermore, Angola's location along the western coast of Africa means that it is not directly impacted by the hurricanes that originate in the Cabo Verde region. These hurricanes typically affect the Caribbean or the southeastern United States, rather than the African continent.

The closest tropical cyclones to Angola have originated in the Cape Verde islands

Angola is seldom hit by hurricanes as easterly winds tend to carry storms away from the African landmass. Tropical cyclones affecting the continent usually originate from the southwest Indian Ocean, with locations further north generating some of the world's strangest tropical systems. Northern Africa is bordered by three basins: the Arabian Sea to the east, the Mediterranean Sea to the north, and the Atlantic Ocean to the west.

The Cape Verde islands, located off the west coast of Africa, are often the birthplace of Atlantic hurricanes, also known as Cape Verde hurricanes. These hurricanes are large and intense, benefiting from the warm open ocean that allows them to develop and strengthen before encountering land. On average, there are about two Cape Verde hurricanes per Atlantic hurricane season, and they are usually the most intense storms of the season.

Cape Verde hurricanes typically develop from tropical waves that form in the African savanna during the wet season and then move into the African steppes. These disturbances move off the western coast of Africa and become tropical cyclones within 10 to 15 degrees latitude, or 1,100 to 1,600 kilometres, of the Cape Verde Islands. This area comprises the tropical latitudes east of the 40th meridian west. The Cape Verde islands themselves have only one tropical cyclone monitoring station, located in Sal.

Several hurricanes have originated near the Cape Verde islands and gone on to impact Angola and the surrounding region. For example, the 1900 second hurricane, which formed on September 10, bypassed the Cape Verde islands to the west, reaching Category 1 strength. On August 25, 1901, the sixth hurricane of that year was observed east of Boa Vista in the Cape Verde islands and struck the island a few hours later. More recently, in 2015, Hurricane Fred reached Category 1 strength as it hit Cape Verde, resulting in hurricane conditions across many of the islands and causing several fatalities.

Tropical cyclones are fuelled by warm ocean temperatures

The heat energy from the ocean acts as an accelerator for tropical cyclones, causing inland regions to suffer less damage than coastal regions. Tropical cyclones draw in air from a large area and concentrate its water content into precipitation over a much smaller area, leading to multi-hour or multi-day extremely heavy rain up to 40km from the coastline. This can result in river flooding, overland flooding, and the overwhelming of local water control structures.

Climate change is warming ocean temperatures, leading to a greater amount of fuel for tropical cyclones. This has resulted in an increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir-Simpson scale since 1979. Warmer air can also hold more water vapour, leading to an increase in rainfall rates. In addition, sea level rise will increase storm surge levels, further exacerbating the dangers to coastal communities.

While tropical cyclones can form in several regions around Africa, they seldom occur in Angola as easterly winds carry the storms away from land. However, one notable exception is the 1991 Angola tropical storm, which is the only recorded tropical cyclone in the eastern South Atlantic.

Cyclones are becoming more frequent and intense in Africa due to global warming

Africa is bordered by four cyclone-producing tropical ocean basins—the Indian Ocean, the Atlantic Ocean, the Mediterranean Sea, and the Arabian Sea. While cyclones in Africa are rare, they do occur, and their frequency and intensity are increasing due to global warming.

The impact of global warming on the frequency and intensity of cyclones in Africa is evident. Since the 1970s, Africa has experienced four times as many storms and more than double the number of cyclones. During the 2021-2022 season, for example, there were six cyclones that originated in the Indian Ocean, compared to an average of three in previous years. This increase in cyclone activity has had devastating consequences for the continent, with Cyclone Idai in 2019 being the deadliest and most costly cyclone ever to hit Africa, causing over 1,000 deaths and approximately $3.25 billion in damages.

The Intergovernmental Panel on Climate Change (IPCC) predicts that global warming will lead to an increase in the frequency and intensity of heavy rainfall events in most of tropical Africa. This will result in a significantly higher risk of flooding, particularly in Central Africa, where runoff in the Congo River basin is projected to increase by 50%. Additionally, the IPCC expects global warming to increase rainfall in parts of the Greater Horn of Africa by over 40%. This has already contributed to the worst desert locust outbreak in East Africa in the past 25 years.

The increase in cyclone frequency and intensity in Africa is closely linked to rising ocean temperatures. Warmer ocean temperatures provide more energy for storms developing over the oceans, resulting in more intense rainfall and higher wind speeds. This, in turn, leads to more damaging cyclones that cause extensive damage to crops, homes, and infrastructure. Furthermore, the warming climate increases the amount of moisture the atmosphere can hold, with a 7% increase in water vapor for every 1°C rise in temperature. This results in wetter storms and contributes to record-breaking rainfall.

The impact of these more frequent and intense cyclones is exacerbated by socioeconomic stressors and conflicts in affected regions. The distribution and seasonal transmission of vector-borne diseases, such as malaria, yellow fever, and dengue, are also expected to increase with rising temperatures, exposing tens of millions of people in East and Southern Africa to these diseases.

To adapt to the increasing frequency and intensity of cyclones, vulnerable communities in Africa need to design solutions and implement disaster risk reduction measures. Early warning systems, improved housing, and the expansion of canal systems are some of the strategies being employed to mitigate the impacts of these powerful storms.

The African Easterly Jet, a strong area of high-altitude winds, is key to the formation of tropical cyclones

Tropical cyclones are massive tropical cyclonic storm systems with winds exceeding 74 miles/hour. They are called hurricanes in the Atlantic Ocean and eastern Pacific Ocean, typhoons in the western Pacific, and simply cyclones in the southern hemisphere. Tropical cyclones are dangerous because of their high winds, storm surges, and severe thunderstorms. Although death due to hurricanes has decreased in recent years due to better forecasting and early warning systems, the economic damage from hurricanes has increased as more development takes place along coastlines.

The African Easterly Jet is a strong area of high-altitude winds that plays a crucial role in the formation of tropical cyclones. The African Easterly Jet, also known as the African easterly wave, is a large-scale atmospheric circulation pattern that originates over Africa and moves westward over the Atlantic Ocean. It is characterised by a band of strong upper-level winds blowing from the east, and it is this easterly movement that carries storms away from land, making direct impacts on the African continent relatively rare.

The African Easterly Jet is closely associated with the formation of tropical cyclones in two main ways. Firstly, it provides the necessary atmospheric instability for cyclone development. This instability, combined with warm ocean waters, creates an environment favourable for the intense thunderstorms that fuel tropical cyclones. Secondly, the African Easterly Jet influences the movement and track of tropical cyclones. Once formed, these storms are steered by the prevailing winds and other wider environmental conditions within the African Easterly Jet, which determine their path and intensity.

The African Easterly Jet is just one of several key factors that contribute to the formation of tropical cyclones. Other essential conditions include warm ocean waters of at least 26.5-27°C throughout a sufficient depth, a moist atmosphere, low vertical wind shear, and a pre-existing near-surface disturbance. When these factors converge in the tropical regions near the equator, they create the ideal environment for the birth of a tropical cyclone.

While the African Easterly Jet plays a significant role in the formation and behaviour of tropical cyclones, it is just one piece of a complex puzzle. The interaction of multiple factors, including the Coriolis effect, atmospheric pressure systems, and ocean temperatures, all come together to shape the development and trajectory of these powerful storms.

Frequently asked questions