Tropical Storms

What Are Tropical Storms?

Tropical storms (also called hurricanes in the Atlantic, typhoons in the Pacific and cyclones in the Indian Ocean) are intense, rotating low-pressure weather systems that form over warm tropical seas. They bring very strong winds (>117 km/h to qualify as a hurricane), torrential rainfall, and storm surges.

Distribution — Where Do They Form?

Tropical storms form between 5° and 30° north or south of the Equator — predominantly over the tropics — where sea surface temperatures (SSTs) exceed 26.5°C. They are found in:

• Atlantic/Caribbean (hurricane belt): affects Caribbean Islands, USA, Mexico, Central America
• Western North Pacific (typhoon belt): affects Philippines, Japan, Vietnam, China
• Bay of Bengal/Indian Ocean: affects Bangladesh, India, Myanmar
• Southern Indian Ocean/Coral Sea: affects Mozambique, Madagascar, NE Australia

They do not form:

• At the Equator (no Coriolis effect to generate rotation)
• Over cold water
• Outside hurricane seasons (generally June–November in the Northern Hemisphere)

Formation — How Do They Develop?

A tropical storm develops in stages:

1. Warm sea evaporates: ocean water (>26.5°C) evaporates, creating warm, moist, unstable air
2. Air rises rapidly: the warm air rises in a column — creating a low-pressure centre at the surface
3. Coriolis effect: the Earth's rotation causes the rising air to spin (anticlockwise in the N hemisphere, clockwise in S hemisphere)
4. Condensation and latent heat: as air rises and cools, water vapour condenses → releases latent heat → warms the air → makes it rise faster → more evaporation → positive feedback loop
5. Eye of the storm: the very centre — a calm area of descending air, 10–50 km wide; lowest pressure; clear skies
6. Eyewall: surrounding the eye — the most intense winds and rainfall

The storm intensifies as long as it is over warm water. When it crosses land or cool water, it loses its energy source and weakens rapidly.

Effects of Tropical Storms

Primary Effects (direct, immediate)

• High winds destroy buildings, uproot trees, damage infrastructure
• Torrential rainfall causes flash flooding and river flooding
• Storm surge: a rise in sea level pushed ashore by low pressure and wind — the deadliest effect

Secondary Effects (indirect, later)

• Disease (cholera, typhoid) from contaminated water supplies
• Homelessness → exposure; mental health impacts
• Economic disruption: damaged agriculture, tourism, infrastructure
• Landslides triggered by heavy rainfall

Effects vary by development level

In HICs (e.g., USA): better construction standards, emergency services, early warning systems → fewer deaths but more economic damage In LICs/NEEs (e.g., Bangladesh, Philippines): more deaths; poorer infrastructure; less capacity to respond and recover

Case Study 1 (HIC): Hurricane Katrina, USA, 2005

• Category 4 hurricane; made landfall on Gulf Coast (Louisiana) on 29 August 2005
• Causes of disaster: poor levée system in New Orleans; slow government response (FEMA criticised); large low-income population unable to evacuate
• Effects: 1,800+ deaths; $125 billion damage; 80% of New Orleans flooded; 500,000 displaced; Superdome used as a shelter of last resort
• Responses: National Guard deployed; FEMA coordinated relief; massive reconstruction ($120 billion federal aid); new levée system built

Case Study 2 (LIC): Typhoon Haiyan (Yolanda), Philippines, 2013

• One of the most powerful tropical cyclones ever recorded; wind speeds >310 km/h
• Devastated the Visayas islands, especially Tacloban City
• Effects: 6,300+ deaths; 4 million homeless; storm surge up to 5 m swept through Tacloban; 90% of structures in Tacloban destroyed; $2 billion economic damage
• Responses: International aid (UK £100 million), Philippines military, NGOs (Oxfam, Red Cross) deployed; UN coordinated largest single aid operation; long-term reconstruction still ongoing years later

Management of Tropical Storms

Prediction and Monitoring

• Satellite imagery: GOES and METEOSAT satellites track development in real time
• Hurricane hunter aircraft: fly into the storm to measure wind speed, pressure
• Computer modelling: predict track and intensity — accuracy has improved dramatically since 2000
• The Saffir-Simpson scale classifies hurricanes (Categories 1–5) by wind speed — helps communicate risk to public

Preparation

• Building codes: reinforced structures, hurricane shutters
• Evacuation plans: mandatory evacuation orders for coastal zones
• Emergency supply stockpiles
• Education and community drills

Response and Recovery

• Government emergency services; military; international aid
• Temporary shelters → reconstruction
• Insurance systems (more effective in HICs)

Climate Change and Tropical Storms

Climate change is expected to make tropical storms:

• More intense (higher category) because warmer SSTs provide more energy
• Wetter — warmer atmosphere holds more moisture → more rainfall → greater flood risk
• Reaching further poleward as warm water extends
• Possibly fewer in total number but more extreme — the proportion of Category 4–5 storms is increasing

WJEC Exam Tips

• Always include a named case study — one HIC and one LIC for maximum evaluation marks
• Use cause, effect, response structure
• For 8-mark questions: evaluate whether management is more effective in HIC vs LIC — rich countries cope better but poverty drives vulnerability
• Climate change impact on tropical storms is often a 4–6 mark question