Hurricanes are gigantic tropical storms that can be hundreds of kilometres wide. They bring along very strong winds and a lot of rainfall. They often cause flooding near the coasts and sea levels rise.
Hurricanes occur in many parts of the world. In the Pacific Ocean they are called typhoons and in Australia they are willy-willies. In the Atlantic Ocean and the Caribbean Sea they are called hurricanes.
Hurricanes are born over tropical oceans, usually during late summer and early autumn. They need two things to get them started: heat and moist air.
During the summer the ocean surface heats up and warm moist air starts to rise. Cool air sinks down to replace it. This creates an area of low pressure.
The rotation of the earth creates winds around the centre of such a low pressure area. In the northern hemisphere the air moves counterclockwise, in the southern part clockwise. Such a system is called a cyclone.
When warm air rises it cools and creates clouds. Soon, thunderstorms form and it starts to rain.
All hurricanes begin as cyclones but not all cyclones become storms or hurricanes. Some die out a few days after they start. They don’t have enough energy to become a hurricane. When winds are stronger than 119km an hour a storm officially becomes a hurricane.
The centre of a hurricane is called the eye, a calm area with little rainfall. It is about 30 to 50km wide. Inside the eye the sea can rise up to one metre because the air moves up.
The eyewall is around the eye. This is an area of thunderstorms, rain and the strongest winds—up to 300km an hour.
Then come long bands of rain clouds that are curved towards the centre of the hurricane.
In the northern hemisphere hurricanes normally move in a westward direction and then they turn north and northeast. Their path takes them away from the warm tropical water of the equator. When hurricanes move over colder water or over land they lose a lot of their energy. They slow down and as time goes on, they disperse. In the southern hemisphere their path leads them to the south and southeast.
When a tropical storm forms over the Caribbean Sea it gets a name. Every year the first storm of the season is given a name that starts with the letter A, the second storm gets a name starting with B and so on.
Years ago only women's names were used for tropical storms. Today male and female names alternate – for example, the first storm is named Alexandra, the second one Billy, then Catherine etc.
Each year new names are used so that you can connect a storm to a certain year.
|Category 1||119—153km/h||Winds cause only small damage to houses and building.|
|Category 2||154—177km/h||Storms can tear away roofs, damage doors and windows. Boats often break away from docks.|
|Category 3||178—209km/h||Winds can destroy mobile homes. Areas lower than 1.5 metres above sea level may be flooded.|
|Category 4||211—249km/h||Areas lower than 3m above sea level are flooded. Coastal areas (up to 10km) are evacuated.|
|Category 5||more than 249km/h||These are the most powerful hurricanes. Places within 15km of the coast are evacuated.|
Hurricanes can cause a lot of damage. They bring along strong winds and heavy rainfall. In 2005, Hurricane Katrina hit the Gulf Coast and destroyed New Orleans. Many people died and hundreds of thousands had to leave the city. When a hurricane reaches land the winds can knock down small buildings, tear off roofs of houses and uproot trees. Waves produce floods around the coast. The surface water can rise up to 5 metres. This is called a storm surge.
Hurricanes are causing more and more damage throughout the Gulf Region, mainly because the population is constantly growing.
When a hurricane is sighted, television and radio stations may broadcast a hurricane watch. This means that a hurricane may hit the area in the following 36 hours. If the weather gets worse there is a hurricane warning, which means that a hurricane is expected in the area in the following 24 hours.
Many things can be done to protect yourself and your property during a hurricane:
• Keep emergency supplies of food and water.
• Keep a battery-powered radio ready in case the power goes out. Listen to the instructions you get.
• Keep the gas tank of your car full, in case you have to leave quickly.
• Protect your house by nailing plywood over the windows and doors. Tie down loose objects.
• Find out which roads are best to take you away from the storm.
• Leave your house as soon as you are ordered to evacuate.
On Monday, August 29, 2005 Hurricane Katrina hit the American coast near New Orleans. The storm had formed over the Caribbean Sea almost a week earlier. As it moved on towards the American coastline it grew more and more powerful. It became a Category 5 hurricane and the fourth largest storm that has ever been recorded in the Atlantic Ocean. Winds reached speeds of over 340km an hour. Although the centre of the hurricane did not pass directly over New Orleans most of the city was flooded by the storm.
New Orleans is located in a really dangerous area. It lies above the Gulf of Mexico where many storms and hurricanes pass through. The Mississippi River also runs through the middle of the city. Because most of New Orleans lies below sea level, high banks of earth, called levees, were built around the city to protect it from flooding. Thousands of pumps have been installed to drain the water away.
Katrina brought along heavy rainfall and parts of the levee broke. About 80% of the city was flooded. Shortly before the storm hit New Orleans about 20,000 people were able to escape to the Superdome, one of the town's largest stadiums.
Most of the city's population was evacuated, but about one hundred thousand had to stay behind, mostly poor people and blacks who had no cars and couldn’t get out. They were trapped in the floods for days without power and water.
In the days after the disaster chaos spread throughout New Orleans. People broke into shops and stole things they needed, like food and water. Violence increased and gun shots could be heard throughout the city. Many people were trapped on rooftops for days before they got any help.
The government and the city authorities were not very well prepared for such a disaster. There were no plans for getting people out of the city. President Bush waited for four days before he visited the region. Thousands of people died in one of the biggest catastrophes in American history.