Storms - Hurricanes (Elementary)

Hurricanes are fierce spinning storms. They are also called tropical cyclones. They start over warm, tropical waters. They grow into giant cyclones, powered by the wind. A hurricane can do terrible damage to anything in its path.

Hurricanes start as tropical storms. They start in the warmer waters of the northern Atlantic – like off the coast of Florida. This area is called the tropics or subtropics. Hurricanes are called by many names. The hurricanes that form in the western Pacific Ocean are called typhoons. The hurricanes in India are often called cyclones.

Tropical storms form because the tropics have lots of warm sunshine that heats the ocean. The ocean water turns to water vapor (it evaporates) and into rising cumulus clouds. In the tropics, these clouds often become thunderstorms by late afternoon. If many thunderstorms form in a row in this region it is called a squall line. As a squall line passes, it brings gusty wind and heavy rain.

If a line of tropical thunderstorms form over warm ocean water with humid air and winds, this can form a tropical wave. If it gets windier, a tropical wave can grow into a tropical depression. Soon it can grow into a tropical storm. This is when it gets a name. Sometimes a tropical storm can grow into a hurricane. It is not a hurricane until its winds reach 75mph (64 knots).

The National Weather Service started naming hurricanes with women’s names in 1953. In 1978, storm names began to take turns between male and female names. These names could be Spanish, French or even Dutch. Every year, the storm names are decided ahead of time. The names are picked by a group of people from the World Meteorological Organization. If a bad storm takes many human lives, that name is never used again.

An average hurricane is about 300 miles (about 500 km) wide. They are circular storms that spin counter-clockwise in the Northern half of the Earth (Northern Hemisphere). They wrap around a central eye. Hurricanes in the Southern half of the Earth (Southern Hemisphere) spin clockwise! Hurricanes form between 5° and 20° latitudes on the globe. They do not form on the equator. This is because there is no spinning wind force at the equator.

Hurricanes build when winds over the ocean meet to form a “wave” of low pressure. Low pressure makes warm air rise and cold air sink (convection). This happens mostly from June through November when the ocean temperature is about 80° (26°C).

Scientists think that all the hurricanes that form in the Atlantic begin with a tropical wave over Africa. This only happens if Africa is having a rainy year. In Africa is dry, there are fewer hurricanes over the Atlantic. Most hurricanes last less than a week. Hurricanes begin to lose power when they hit colder water or land.

The eye of a hurricane has few clouds and only light wind. When the eye of a hurricane passes over an area, sometimes people think the storm is over. As a matter of fact, this is a very dangerous time to be outside during a hurricane. The eye of a hurricane is surrounded by a ring of strong thunderstorms called the eye wall. The hurricane eye wall has some of the storm’s strongest and most damaging wind. As the eye passes over an area, the eye wall hits. Serious damage can result from the wind, rain and lightning in the eye wall. The high winds of a hurricane come with heavy rain and big waves. This can cause dangerous flooding.
 

The deadliest hurricane on record in the United States happened in 1900. It hit Galveston, Texas. Though it was not the most powerful hurricane on record, it caused the most deaths – more than 6,000 people. This happened for several reasons. First, in 1900, weather officials did not have the modern technology we have today for tracking storms. They could not judge where the hurricane would travel in time to warn people. The second reason is that the Weather Bureau thought that a hurricane warning might scare people. This policy changed after that storm.

In more recent history, Hurricane Katrina hit U.S. shores at New Orleans, Louisiana in 2005. The storm surge destroyed the levee protecting the city. New Orleans was flooded. More than 1,300 people died in the storm and the following flood.

1. A tropical storm is called a hurricane when its winds are more than 74 miles per hour (64 knots).
2. An average hurricane is about 300 miles (about 500 km) wide.
3. Hurricanes are circular storms that spin counter clockwise in the Northern Hemisphere. They wrap around a central eye.
4. In the Southern Hemisphere, hurricanes spin clockwise.
5. The eye of a hurricane has few clouds and only light wind.
6. When the eye of a hurricane passes over an area, the storm is not over!
7. The eye of a hurricane is surrounded by a ring of strong thunderstorms called the eye wall.
8. The eye wall has some of the storm’s strongest and most damaging wind.
9. The high winds of a hurricane come with heavy rain and big waves.
10. Hurricanes form best when the ocean temperature is about 80° (26°C).
11. Hurricanes form best from June through November.
12. Hurricanes form between 5° and 20° latitudes.
13. Hurricanes do not form on the equator (latitude 0°) because there is no spinning wind force there.
14. Hurricanes start when a low pressure area over the ocean leads to warm air rising and cold air sinking (convection).
15. Hurricanes may form in the Atlantic when there is a tropical wave over a rainy season in Africa.
16. Most hurricanes last less than a week. They begin to lose power when they hit colder water or land.