A storm is coming toward the shore. Dark clouds fill the horizon.
At first it seems to be a large but ordinary storm.
But the rain falls more heavily than usual.
The wind begins to blow faster and faster, more than one hundred kilometers per hour.
Soon the wind shakes the street signs back and forth, as if an invisible giant were trying to pull them out of the Earth.
Trees begin to fall. The force of the wind rips roofs from buildings.
The wind has pushed the ocean waves farther inland.
Suddenly the ocean seems to rise up—as if the sea level were suddenly six meters higher.
The water surges forward and washes away everything that is not secure.
This is a hurricane: a storm that can cover an area 800 kilometers wide and whose clouds can tower 16 kilometers high.
Also known as cyclones and typhoons, hurricanes are the largest and most damaging storms on Earth.
The word "hurricane" comes from Hurakan, the name of the Caribbean god of storms.
These giant storms develop in different tropical regions.
The storms from the Caribbean and the Gulf of Mexico are called hurricanes.
In India, they are called cyclones, and in the Pacific, they are typhoons.
Hurricanes form in an unusual way. They do not begin as a single storm that slowly grows.
Near the equator, large thunderstorms tend to rotate.
This movement is caused by the Earth's rotation and the regular direction of the Earth's winds near the equator.
If several tropical thunderstorms are close together, they can merge to form a single giant storm called a hurricane.
Hurricanes always rotate. Some rotate clockwise, some counterclockwise.
Hurricanes that rotate clockwise are formed south of the equator; hurricanes that rotate counterclockwise are formed north of the equator.
At first glance, a hurricane may appear to be just a gigantic, swirling storm cloud, but hurricanes have a complicated structure.
A hurricane's winds rotate faster and faster the closer they get to its center.
But right in the middle is the eye of the hurricane, where there is almost no wind, clouds, or rain.
The eye of a hurricane can be up to fifty kilometers wide.
Immediately surrounding the eye of a hurricane is a towering wall of cloud called the eyewall.
Here, the hurricane's wind speed is fastest, so fast that it can produce tornadoes with winds of almost five hundred kilometers per hour.
Hurricanes are formed over areas of warm ocean and are fed by the humid air above the water.
As long as the hurricane stays over the warm ocean water, its strength increases.
The warm air rises, generating wind and pulling in more humid air to fuel its storm.
When a hurricane moves over land or cool water, it begins to weaken.
But hurricanes are so strong that it can take up to ten days for one to lose its power.
The World Meteorological Organization is responsible for naming hurricanes.
Each year hurricanes are named in alphabetical order, alternating between masculine and feminine names.
Not all the letters of the alphabet are used to begin the name of a hurricane.
Q, U, X, Y, and Z are omitted, leaving only 21 letters of the alphabet available.
If more than 21 hurricanes form in one year, the letters of the Greek alphabet are used.
The twenty-second hurricane would be named Alpha, the twenty-third would be named Beta, and so on.
When a hurricane has caused a terrible tragedy,
a country can request that the name of the hurricane be retired so that no future hurricane will have that name again.
Just as storms can differ in the speed of their winds and the amount of rain they cause, so can hurricanes.
Hurricanes are rated from categories one to five, category five being the strongest.
The system of classifying hurricanes is called the Saffir-Simpson hurricane scale.
Even a category one or category two hurricane can have a disastrous impact.
A slow-moving hurricane can drop a tremendous amount of rain, causing landslides or floods.
But in general, the higher the category number, the more dangerous the hurricane is to property and people.
The high winds of a hurricane can push the surface of the ocean into a tall wave.
When this powerful wave hits the shore, it is called the storm surge.
Wind speed and the level of the storm surge are the primary characteristics used to classify hurricanes.
Hurricanes are dangerous in many ways. People can be killed or injured by the flying debris propelled by their powerful winds.
After the hurricane has passed, many may die from disease, since sanitation systems frequently break down during a hurricane.
But 90 percent of the victims of hurricanes are drowned by the storm surge.
Some hurricanes have left 150 kilometers of coastal land submerged underneath 3 meters of water.
Many parts of the world have been repeatedly struck by hurricanes.
With millions of people living in big coastal cities, large populations are at risk.
In response to the threat of hurricanes, governments in these areas have developed evacuation plans.
Unfortunately meteorologists cannot perfectly forecast where and when a hurricane will hit land.
Because it is hard to evacuate whole cities with only a few days' notice, many governments provide hurricane shelters in vulnerable areas.
Sometimes these are large public buildings, such as stadiums.
Other shelters are specifically designed to be used only during hurricanes.
A powerful hurricane can leave chaos in its wake; bridges can be torn down, electricity and sanitation systems can be destroyed.
It is recommended that people who live in areas affected by hurricanes store enough food and drinking water to last several days.
The food should be canned and nonperishable.
It may be a long time before help can arrive, so it is important to be prepared.
Global warming may make coastal regions even more vulnerable to damage by hurricanes.
Hurricanes gain their strength from warm water in tropical regions.
If global warming increases, so will the temperature of the oceans.
Higher temperatures, it is believed, will lead to more hurricanes than before—and these hurricanes are likely to be more powerful.