Weather, Climate and Ecosystems » Formation of tropical storms and impacts

What you'll learn this session

Study time: 30 minutes

How tropical storms form and the conditions needed for their development
The structure and features of tropical storms
How climate change affects tropical storms
Primary and secondary impacts of tropical storms
Case studies of major tropical storms and their effects
How communities prepare for and respond to tropical storms

Formation of Tropical Storms

Tropical storms (also called hurricanes, cyclones, or typhoons depending on where they occur) are powerful weather systems that form over warm ocean waters. They can cause devastating damage when they make landfall.

Key Definitions:

Tropical storm: A large, rotating weather system with wind speeds of at least 63 km/h that forms over tropical or subtropical waters.
Hurricane/Cyclone/Typhoon: A tropical storm with sustained wind speeds of at least 119 km/h.
Eye: The calm, clear centre of a tropical storm.
Eye wall: The ring of thunderstorms around the eye where the most severe weather occurs.
Storm surge: An abnormal rise in sea level accompanying a tropical storm.

🌊 Conditions for Formation

Tropical storms need specific conditions to form:

Ocean water temperature of at least 27°C to a depth of at least 60m
Location at least 5° north or south of the equator (for Coriolis effect)
High humidity in the lower atmosphere
Little wind shear (change in wind direction with height)
Pre-existing weather disturbance or low-pressure system

🌪 Formation Process

Tropical storms form through a series of steps:

Warm ocean water evaporates and rises
Water vapour condenses, releasing latent heat
Air continues to rise, creating low pressure at the surface
More air flows in to replace rising air
Coriolis effect causes the system to rotate
As the system strengthens, it develops a clear eye

Structure and Features of Tropical Storms

Tropical storms have a distinctive structure that helps meteorologists track and predict their behaviour.

Diagram showing the structure of a tropical storm

🟠 The Eye

The eye is the calm centre of the storm:

Typically 30-65 km in diameter
Clear skies and light winds
Lowest pressure in the storm
Surrounded by the most violent part of the storm (the eye wall)

🌩 Spiral Rainbands

These bands of clouds and precipitation:

Rotate around the eye
Produce heavy rainfall
Can extend hundreds of kilometres from the centre
Often produce tornadoes

💧 Storm Surge

A dangerous rise in sea level:

Can reach 6+ metres in height
Often causes more damage than winds
Worst on the right side of the storm (in Northern Hemisphere)
Amplified by high tide and shallow coastal waters

Climate Change and Tropical Storms

Scientists have found evidence that climate change is affecting tropical storms in several ways:

Increased intensity: Warmer oceans provide more energy for storms to intensify
More rainfall: Warmer air holds more moisture, leading to heavier precipitation
Slower movement: Some evidence suggests storms are moving more slowly, increasing flooding risk
Wider range: Areas previously less affected may see more tropical storms as oceans warm
Rapid intensification: More storms are strengthening quickly, giving less warning time

Impacts of Tropical Storms

⚠ Primary Impacts

These are the immediate effects of the storm itself:

Strong winds damage buildings, infrastructure and vegetation
Heavy rainfall causes flooding and landslides
Storm surges inundate coastal areas
Large waves damage coastal structures
Deaths and injuries from collapsing structures, flooding, or debris

🚧 Secondary Impacts

These occur as a result of the primary impacts:

Water contamination leading to disease outbreaks
Power outages affecting hospitals and essential services
Food shortages due to crop damage and supply chain disruption
Economic losses from damage to businesses and infrastructure
Displacement of people from damaged homes
Mental health impacts from trauma and stress

Case Study: Hurricane Katrina (2005)

Hurricane Katrina was one of the deadliest and most destructive Atlantic hurricanes in US history.

Formation: Developed over the Bahamas on August 23, 2005
Strength: Category 5 at peak, Category 3 at landfall
Primary impacts:
- Storm surge up to 8 metres high
- Levee failures flooded 80% of New Orleans
- Wind damage across 233,000 square kilometres
- 1,833 people killed
Secondary impacts:
- Over 1 million people displaced
- $125 billion in damage
- Oil production disrupted, causing fuel shortages
- Long-term mental health issues for survivors
- Environmental damage from toxic floodwaters
Response issues: Slow emergency response, inadequate evacuation plans and poor coordination between agencies worsened the disaster

Responding to Tropical Storms

Communities in tropical storm-prone regions have developed various strategies to prepare for and respond to these disasters:

🚨 Preparation

Early warning systems
Evacuation plans and routes
Storm-resistant building codes
Public education campaigns
Emergency supply stockpiling

🚑 Immediate Response

Search and rescue operations
Emergency medical services
Temporary shelter provision
Distribution of food and water
Restoration of critical infrastructure

🏠 Long-term Recovery

Rebuilding stronger infrastructure
Financial assistance programs
Mental health support
Policy changes to improve resilience
Environmental restoration

Comparing Impacts: HICs vs LICs

The impacts of tropical storms vary significantly between High-Income Countries (HICs) and Low-Income Countries (LICs):

🏧 High-Income Countries

Better early warning systems
More storm-resistant infrastructure
Better-resourced emergency services
Higher economic losses but lower death tolls
More insurance coverage
Faster recovery times
Example: USA (Hurricane Harvey, 2017)

🏚 Low-Income Countries

Less developed warning systems
More vulnerable infrastructure
Limited emergency response resources
Higher death tolls but lower economic losses
Limited insurance coverage
Longer recovery times
Example: Haiti (Hurricane Matthew, 2016)

Case Study: Typhoon Haiyan (2013)

Typhoon Haiyan (locally known as Yolanda) struck the Philippines in November 2013 and demonstrates the severe impacts tropical storms can have on developing nations.

Formation: Developed in the western Pacific Ocean
Strength: One of the strongest tropical cyclones ever recorded, with sustained winds of 315 km/h
Primary impacts:
- Storm surge up to 5-7 metres high
- Over 6,300 people killed
- Widespread destruction of homes and infrastructure
- 90% of buildings destroyed in some areas
Secondary impacts:
- 4 million people displaced
- $2.2 billion in damage
- Widespread power and water outages
- Food shortages and price increases
- Disease outbreaks in crowded evacuation centres
Response: International aid was crucial, with over 40 countries providing assistance, but coordination challenges delayed help reaching remote areas

Summary

Tropical storms are powerful weather systems that form over warm ocean waters and can cause devastating impacts when they make landfall. They require specific conditions to form, including warm ocean temperatures and the Coriolis effect. Climate change is likely making tropical storms more intense and potentially more frequent in some regions.

The impacts of tropical storms include both primary effects (like wind damage and flooding) and secondary effects (like disease outbreaks and economic losses). These impacts are typically more severe in low-income countries, which often have less resilient infrastructure and fewer resources for preparation and response.

Understanding how tropical storms form and their potential impacts is crucial for developing effective strategies to reduce risk and build community resilience in vulnerable coastal regions around the world.