Download Storm Lecture - Hurricanes

Storm Lecture - Hurricanes
About This Storm
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. They can do terrible damage to anything in their
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.
What Events Form This Kind of Storm?
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 grows 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 counterclockwise 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.
Weather Conditions That Are Good for This Kind of Storm
Hurricanes build when winds over the ocean meet up to form a “wave” of low pressure. Low pressure
makes warm air rises 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.
Storm Dangers
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.
Historic Examples of This Kind of Storm
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 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 following flood.
Quick Storm Facts
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 with 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.