Tropical Cyclone Formation (Cambridge (CIE) IGCSE Environmental Management): Revision Note

What conditions are needed for tropical cyclone formation?

• Tropical cyclones are among the most powerful natural hazards on Earth

• Understanding how they form, how they affect people, and how we can manage their impacts is important

What's the difference between hurricanes, cyclones, and typhoons?

• They all describe the same type of storm, but the name varies by region

• They are known as:

  • Typhoons in the South China Sea and the western Pacific Ocean

  • Hurricanes in the Gulf of Mexico, the Caribbean Sea and the west coast of Mexico

  • Cyclones in the Bay of Bengal, the Indian Ocean and northern Australia

Development of tropical cyclones

• Tropical cyclones are rotating, intense low-pressure systems (below 950mb)

• They need specific conditions to form

  • Form between 5° and 30° latitude north or south of the Equator

    • Cyclones require the Coriolis effect to spin, which is too weak at the Equator

    • Therefore, they form away from the Equator, usually between 5° and 30° latitude

    • They do not form at higher latitudes because the water is too cold

  • Ocean temperature of at least 27 °C

    • Warm water is essential because it provides the heat energy needed to drive the storm

    • Ocean temperatures must be in excess of 27°C

    • Warm water evaporates rapidly, adding heat and moisture to the rising air

    • This fuels towering cumulonimbus clouds and intense rainfall

    • Warm water = more evaporation = more latent heat = stronger cyclone

  • Ocean depth of at least 60 m

    • Warm water must extend to at least 60 metres in depth

    • Deep warmth ensures the storm continues to gain energy without mixing with cooler water from below

    • Shallow warm layers are quickly disrupted by strong winds

• Tropical cyclones begin when tropical oceans are at their warmest, which is usually late summer (Nov-April in the southern hemisphere and June-Nov in the northern hemisphere)

  • The Pacific Ocean sees the largest number of tropical storms, followed by the Indian Ocean, and lastly, the Atlantic

  • Tropical storms in the western Pacific are the strongest 

Impacts of tropical cyclones

• Cyclones affect large areas because they combine high winds, intense rainfall, storm surges, and flooding

• Damage to buildings and infrastructure

  • Roofs ripped off; buildings collapse

  • Power lines, roads, bridges and communication networks are destroyed

• Loss of crops

  • Crops flattened by wind or drowned by floodwater

  • Saltwater storm surges ruin farmland

• Loss of livestock and habitats

  • Animals drowned or injured

  • Forests uprooted; coastal ecosystems damaged

• Evacuation of people and livestock

  • Millions may be moved to safer areas

  • Displacement disrupts daily life and livelihoods

• Flooding

  • Torrential rain, overflowing rivers and storm surges cause widespread flooding

  • Urban drainage may be overwhelmed

• Landslides

  • Heavy rainfall saturates slopes, triggering landslides

  • Buries homes, roads and farmland

• Contamination of drinking-water supplies

  • Floodwater mixes sewage with clean water

  • Saline intrusion from storm surges pollutes wells and aquifers

• Water-related disease

  • Outbreaks of cholera, dysentery, giardia and other infections

  • Standing water encourages mosquito breeding

• Financial losses

  • Huge repair costs for transport networks, homes, utilities and businesses

  • Loss of agricultural production and tourism

  • Long-term economic disruption

• Human health

  • Injuries and deaths from collapsing structures and debris

  • Psychological stress and trauma after disaster

  • Poor shelter conditions increase sickness