Tropical Storms: Causes, Effects & Responses
Tropical storms are one of the most powerful weather hazards on Earth. Known as hurricanes (Atlantic/NE Pacific), typhoons (NW Pacific), or cyclones (Indian Ocean/South Pacific), these storms can bring devastating winds, torrential rain, and coastal flooding. This lesson covers their formation, effects, and responses, using Typhoon Haiyan (2013) as a key case study.
Where and How Do Tropical Storms Form?
Tropical storms form over warm tropical oceans under specific conditions:
Conditions Needed
| Condition | Detail |
|---|
| Sea temperature | Must be at least 27 °C to a depth of 60–70 metres |
| Location | Between 5° and 30° from the equator (Coriolis effect needed to spin the storm) |
| Low wind shear | Little change in wind speed/direction with altitude (otherwise the storm is torn apart) |
| Atmospheric instability | Warm, moist air must be able to rise rapidly and continuously |
| Time of year | Late summer/autumn when ocean temperatures are highest |
The Formation Process
- Intense solar heating warms the ocean surface, causing warm, moist air to rise rapidly.
- As the air rises, it cools and condenses, releasing latent heat — this provides the energy that drives the storm.
- More warm air is drawn in at the surface to replace the rising air, creating a continuous cycle.
- The Coriolis effect causes the rising air to spin (anticlockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere).
- The storm intensifies as it continues to feed on warm ocean water.
- A central eye forms — a calm area of descending air surrounded by the most intense winds and rainfall (the eyewall).
Structure of a Tropical Storm
- Eye — calm centre, 30–50 km wide, clear skies, light winds.
- Eyewall — surrounds the eye; contains the strongest winds (up to 250+ km/h) and heaviest rainfall.
- Rainbands — spiralling bands of cloud and rain extending hundreds of kilometres from the centre.
- Diameter — typically 400–800 km, but can exceed 1,000 km.
Exam Tip: When explaining tropical storm formation, you must include specific details such as the 27 °C sea temperature threshold and the role of the Coriolis effect. Vague answers about "warm air rising" will not score highly.
Global Distribution of Tropical Storms
Tropical storms only form over warm tropical oceans. They are not found at the equator (insufficient Coriolis effect) or at latitudes above ~30° (water too cool).
The main basins are:
- Atlantic (hurricanes) — Caribbean, Gulf of Mexico, eastern seaboard of the USA
- NW Pacific (typhoons) — Philippines, Japan, China, Vietnam
- NE Pacific (hurricanes) — western coast of Mexico
- Indian Ocean (cyclones) — Bay of Bengal, Arabian Sea, Madagascar, northern Australia
- SW Pacific (cyclones) — northern Australia, Pacific islands
When Tropical Storms Weaken
Tropical storms lose strength when they:
- Move over cooler water (below 27 °C) — their energy source is cut off.
- Move over land — friction slows the wind and the moisture supply is removed.
- Encounter strong wind shear — the storm structure is disrupted.
Effects of Tropical Storms
Primary Effects (direct effects of the storm)
- Extreme winds (up to 300 km/h) — destroy buildings, uproot trees, turn debris into projectiles.
- Torrential rainfall — causes flash flooding and river flooding.
- Storm surge — a rise in sea level caused by low pressure and strong winds pushing water onshore. This is often the deadliest effect.
Secondary Effects (caused by the primary effects)
- Flooding — from rainfall and storm surge; contaminates drinking water.
- Landslides — triggered on saturated slopes.
- Disease — contaminated water leads to outbreaks of cholera, typhoid, and dysentery.
- Homelessness — millions may be displaced.
- Food shortages — crops destroyed, supply chains disrupted.
- Economic damage — cost of rebuilding, loss of industry, reduced tourism.
- Environmental damage — coastal erosion, mangrove destruction, coral reef damage.
Case Study: Typhoon Haiyan, Philippines (2013)
Background
| Detail | Information |
|---|
| Date | 8 November 2013 |
| Category | Category 5 — one of the strongest tropical storms ever recorded |
| Maximum winds | 315 km/h (sustained); gusts up to 380 km/h |
| Storm surge | Up to 5 metres in Tacloban, Leyte |
| Location | Central Philippines (Eastern Visayas) |
| Country type | LIC/NEE (GDP per capita ~$2,800 at the time) |
Primary Effects
- 6,300+ people killed, over 28,000 injured.
- Wind damage — 90% of the city of Tacloban was destroyed.
- Storm surge — a wall of water up to 5 m high swept through Tacloban, the deadliest single effect.
- Over 600,000 people displaced from their homes.
Secondary Effects
- 14.1 million people affected across the Philippines.
- $12 billion in damage — making it the costliest typhoon in Philippine history.
- Agriculture devastated — over 600,000 hectares of farmland destroyed, including coconut plantations that take years to regrow.
- Disease outbreaks — contaminated water caused cases of gastroenteritis and leptospirosis.
- Looting and lawlessness — some areas experienced breakdowns in social order in the days after the storm.
- Emotional and psychological trauma — widespread PTSD, especially among children.
Responses
Immediate responses:
- The Philippine government deployed the military for search and rescue.
- International aid: the UN launched a 301millionappeal;theUKdonated96 million; the US sent an aircraft carrier (USS George Washington) and 1,000 marines.
- Emergency shelters, food, clean water, and medical supplies were distributed by NGOs including the Red Cross and Medecins Sans Frontieres.
- Tacloban airport was cleared within days to allow aid flights to land.
- However, the scale of destruction meant aid was initially slow to reach remote islands and coastal communities.
Long-term responses:
- The government developed a comprehensive "Build Back Better" reconstruction programme.
- "No-build zones" were established along vulnerable coastlines — residents were relocated further inland.
- Mangrove replanting programmes were launched to create natural storm surge barriers.
- Improved early warning systems were installed, including community-level sirens and SMS alerts.
- International agencies funded school and hospital reconstruction to typhoon-resistant standards.
- Livelihood recovery programmes helped farmers replant and fishermen replace boats.
Exam Tip: The AQA specification requires you to study a named example of a tropical storm in an LIC or NEE. Typhoon Haiyan is one of the most commonly used examples. Make sure you know specific facts and figures — the examiner rewards precise data.
Reducing the Risk from Tropical Storms
Prediction and Monitoring
- Satellite imaging tracks storm development and movement in real time.
- Weather stations and ocean buoys measure sea temperature, pressure, and wind speed.
- Computer models predict the storm's likely path (the "cone of uncertainty").
- Forecasters can typically give 3–5 days' warning before a tropical storm makes landfall.
Protection
- Sea walls and storm surge barriers protect coastal communities.
- Building design — reinforced concrete, aerodynamic roof shapes, elevated structures.
- Mangrove conservation — mangroves absorb wave energy and reduce storm surge.
- Land-use planning — avoiding building in the most vulnerable coastal areas.
Preparation