Tropical Storms (Cambridge (CIE) IGCSE Geography) : Revision Note

Tropical storm distribution

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

• They are known as:

  • Typhoons in the South China Sea and west Pacific Ocean

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

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

Development of tropical storms

• Tropical storms require specific conditions to form

  • Ocean temperatures must be in excess of 27°C and to a depth of 50-60 metres

  • Between 5° and 30° north and south of the equator, but not on the Equator, as there is no Coriolis effect

  • When winds converge (meet) near the ocean surface

  • There is low vertical wind shear

  • A deep layer of humid air

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

Characteristics of tropical storms

• Characteristics include:

  • lasting 7-14 days

  • heavy rainfall

  • high wind speeds (over 119 km/h)

  • high waves and storm surges

  • calm eye

  • high winds and heavy rain in the wall of the eye

• Tropical storms can vary in diameter (100 and 1000 km) but generally ranges from 200 to 500 km (124 to 311 miles)

• Winds spiral rapidly around a calm central area known as the eye, with descending cold air, low pressure, light winds, no clouds or rain

• The winds of the storm are not constant across its diameter

  • The outer edges of the storm have lighter wind speeds, smaller and more scattered clouds, rain is less intense, and the temperatures begin to increase

  • The strongest and most destructive winds are found within the eyewall, with spiralling storm clouds, torrential rainfall and low temperatures 

• Tropical storms are rated on the five-point Saffir-Simpson scale based on wind speeds

• Tropical storms are considered major when they reach category 3 and have wind speeds between 111 and 129 miles (178 and 208 kilometres) per hour

• A category 5 storm can deliver wind speeds of more than 157 miles (252 km) an hour

Stages of tropical storm formation

• In the right conditions, a tropical storm can form rapidly

• The formation follows several stages:

  • Warm, moist air rises rapidly, creating an area of low pressure

  • Air from high-pressure regions rushes in to replace the rising air, generating a continuous upward flow

  • As this air rises, it cools, condenses, and releases heat energy, which fuels the tropical storm

  • Air at the top of the storm flows outward from the centre

  • The Coriolis effect causes the rising air to spiral around the centre

  • Some of the air sinks in the middle of the storm, forming the cloudless, calm eye

  • The tropical storm moves westwards from its source 

  • When a tropical storm makes landfall or moves over an area of cold water, it no longer is supplied with warm, moist air and it loses speed and temperature

  • Rainfall and winds decrease

Impacts of tropical storms

• The primary impacts of tropical storms

  • High winds up to 250 km/h uprooting trees, damaging infrastructure and buildings, causing injury and loss of life

  • Intense rainfall leading to flash flooding, damaging property and injuring people from fast-flowing water

  • Storm surges from large areas of low pressure allow the sea level to rise, which, combined with high winds, forces a large mass of water towards land. This erodes beaches, damage sea defences and contaminates farmland and freshwater

  • Coastal flooding caused by intense rainfall and storm surges can affect large areas of low lying land, including farmland and the tourist industry

  • Landslides are triggered because soil becomes saturated due to intense rainfall and in areas with steep slopes where the soil can no longer hold its position, sliding down the slope

• The secondary impacts of tropical storms include

  • People are made homeless, causing distress, poverty, ill-health or death due to lack of shelter. Cost of rebuilding can be expensive and some people may not have insurance

  • Blocked or destroyed roads prevent rescue and emergency vehicles, and aid from getting through

  • Life support systems, hospitals, shops and homes left without power supplies when electricity lines are damaged/destroyed

  • There are risks of fires and explosions as gas lines are broken

  • Clean water supplies are contaminated as sewage overflows, bringing the increased risk of waterborne diseases and death

  • Economic impact to business owners and potential unemployment as businesses are destroyed

  • Storm surge can drown people or cause injuries from the rushing water. Crops, livestock and habitats are destroyed, leading to a shortage of food and potentially famine

    • For instance, Cyclone Idai destroyed almost 715,000 hectares of crops in March 2019, resulting in food shortages in Mozambique

    • The cyclone killed over 1,000 people and affected over 15 million in Mozambique, Malawi, and Zimbabwe

    • It was the second-deadliest tropical cyclone ever seen in the southern hemisphere

Planning, preparation, protection, and prediction of tropical storms

• Level of preparation depends on accurate forecasting and then communications but also level of development

• High Income Countries (HICs) are able to spend money on preparation and high-tech systems of prediction and notification

• Middle Income Countries (MICs) and Low Income Countries (LICs) may find it difficult to buy satellites and monitoring systems or communicate the information to people likely to be affected

• The 4 P's are used to manage tropical storms: planning, preparation, protection, and prediction (for the future)

• These aim to:

  • Save lives

  • Protect personal property and infrastructure

• Planning provides long term strategies to mitigate the impacts of tropical storms

  • Examples include building homes and businesses away from high risk areas, such as the coast

  • Implement building standards to ensure structures can withstand hurricane force winds and storm surges 

    • Areas of poverty lead to poor construction of housing, which is more easily damaged: regardless of level of development

• Preparation involves taking measures to minimise risks and ensure readiness before a tropical storm strikes 

  • Examples include developing emergency response plans

  • Stockpiling supplies and advising people to maintain a survival kit

  • Educating residents about evacuation routes and safety procedures 

  • Reinforcing buildings and securing loose objects that could become projectiles in high winds are also sensible preparations

    • People who know how to react are more likely to survive, as they will evacuate safely 

    • Survival kits can help those who are trapped to survive whilst waiting for help

• Protection involves creating structures that help lessen the effects of tropical storms on both people and property

  • This includes things like building seawalls, levees, and storm surge barriers that can prevent flooding

  • Mangroves are nature's own defence system and can play a crucial role in reducing the impacts of storm surges and coastal erosion when planted

    • Buildings are less likely to be destroyed, so less people will die from collapsing buildings and falling debris

    • Buildings will not be flooded

      This reduces the risk of flooding from overflowing rivers, or from storm surges

• Prediction is understanding where the storm is headed and how strong it’s going to be

  • Early warning systems alert those who are at risk

  • Meteorological agencies combine satellite imagery and weather models with historical data to predict how tropical storms will develop and move

    • This allows time for evacuation, which will reduce the number of deaths and injuries

    • It also means people can protect their homes and businesses from strong winds and flooding