Weather Hazards (Tropical Storms)

Formation of Tropical Storms

Tropical storms, also called hurricanes or cyclones depending on the region, form over warm ocean waters near the equator. The key conditions for their formation include:

• Warm ocean water: Sea surface temperatures must be above about $26^\circ\mathrm{C}$ to provide enough heat and moisture to fuel the storm.
• Low pressure system: Warm air rises from the ocean surface, creating an area of low pressure beneath. This causes surrounding air to rush in, feeding the storm.
• Coriolis effect: The Earth's rotation causes the incoming air to spin, which leads to the characteristic circular motion of tropical storms. This effect is why tropical storms do not form near the equator itself (within about 5° latitude).
• Eye of the storm: At the centre of the storm is the eye, a calm, clear area with very low pressure. Surrounding the eye is the eyewall, where the strongest winds and heaviest rain occur.

The storm gains strength as it moves over warm water, but weakens rapidly once it reaches land or cooler waters.

For instance, a tropical storm forming over the Atlantic Ocean near the Caribbean will draw energy from the warm sea surface and develop a spinning low pressure system due to the Coriolis effect, creating the classic hurricane structure with an eye at its centre.

Characteristics of Tropical Storms

Tropical storms have several defining features that make them hazardous:

• Strong winds: Winds can exceed $120\,\mathrm{km\,h^{-1}}$, causing widespread damage. The strongest winds are found near the eyewall. (Note: Tropical storms typically have wind speeds from 63 to 118 km/h, with hurricanes exceeding 119 km/h.)
• Heavy rainfall: Tropical storms can produce intense rainfall, often over $200\,\mathrm{mm}$ in a short period, leading to flooding.
• Storm surges: The low pressure and strong winds push seawater onto the coast, causing storm surges that can flood coastal areas.
• Duration and size: Tropical storms can last for several days and cover hundreds of kilometres in diameter, affecting large areas.

The combination of these characteristics makes tropical storms particularly destructive when they make landfall.

Impacts of Tropical Storms

Tropical storms cause a range of impacts on people and the environment:

• Damage to buildings and infrastructure: Strong winds can destroy homes, schools, roads, and power lines. Roofs may be torn off and windows shattered.
• Flooding and landslides: Heavy rain causes rivers to overflow and can trigger landslides on steep slopes, damaging farmland and settlements.
• Economic costs: Repairing damage and lost business can cost billions of pounds. Tourism and agriculture often suffer long-term setbacks.
• Social disruption and casualties: People may be injured or killed, and many are displaced from their homes. Essential services like water and electricity may be cut off.

For example, Hurricane Katrina in 2005 caused widespread flooding in New Orleans, destroyed homes, and resulted in over 1,800 deaths, with economic losses estimated at over $\$100$ billion (approximately £80 billion).

Management and Mitigation

Managing tropical storm hazards involves preparation, response, and recovery strategies:

• Monitoring and forecasting: Meteorologists use satellites and radar to track storms and predict their paths and intensity, giving people time to prepare or evacuate.
• Evacuation plans: Authorities develop clear evacuation routes and shelters to move people out of danger zones before the storm arrives.
• Building regulations: In vulnerable areas, buildings are designed to withstand strong winds and flooding, such as using reinforced walls and raising homes on stilts.
• International aid and recovery: After a storm, aid from governments and charities helps rebuild infrastructure, provide food and medical care, and restore communities.
• Community education and preparedness: Public awareness campaigns and drills help people understand risks and how to respond effectively.

These measures reduce the risk to life and property but cannot eliminate all damage.

For example, the Philippines has a well-developed typhoon warning system and evacuation procedures that have saved many lives during recent storms.