WHAT IS A HURRICANE?
A hurricane is an intense, rotating oceanic weather system that possesses
maximum sustained winds exceeding 119 km/hr (74 mph). It forms and
intensifies over tropical oceanic regions.
Hurricane season officially runs from June through November
when the waters of the Atlantic Ocean are warm enough to
produce a tropical cyclone, a category of weather systems
that includes tropical depressions, tropical storms and
The centre is called the eye. In the eye of a hurricane there is
a calm area of blue sky.
Around the eye there are very strong winds – a minimum
speed of 120 kilometres per hour – accompanied by torrential
Hurricanes cause more widespread damage than tornadoes
because they are bigger – some as large as 1,000 kilometres
One of the most destructive effect of a hurricane is the storm
surge, often causing serious flooding.
Every year, the world experiences
hurricane season. During this period,
hundreds of storm systems spiral out
from the tropical regions surrounding the
equa-tor, and between 40 and 50 of
these storms intensify to hurricane
levels. In the Northern Hemisphere, the
season runs from June 1 to Nov. 30,
while the Southern Hemisphere
generally experiences hurricane activity
from January to March. So 75 percent of
the year, it's safe to say that someone
somewhere is probably worrying about
an impending hurricane.
HOW DO THEY BEGIN?
A hurricane builds energy as it
moves across the ocean,
sucking up warm, moist tro-pical
air from the surface and
dispensing cooler air aloft. Think
of this as the storm breathing in
and out. The hurricane
escalates until this "breathing" is
disrupted, like when the storm
makes landfall. At this point, the
storm quickly loses its
momentum and power, but not
without unleashing wind speeds
as high as 185 mph (300 kph)
on coastal areas.
HOW A HURRICANE
WORKS VIDEO LINK
DEFINING A HURRICANE
To understand how a hurricane works, you have to understand the
basic principles of atmospheric pressure. The gases that make
upEarth's atmosphere are subject to the planet's gravity. In fact, the
atmosphere weighs in at a combined 5.5 quadrillion tons (4.99
quadrillion metric tons). The gas molecules at the bottom, or those
closest to the Earth's surface where we all live, are compressed by
the weight of the air above them.
The air closest to us is also the warmest, as the atmosphere is mostly
heated by the land and the sea, not by the sun. To understand this
principle, think of a person frying an egg on the sidewalk on a hot,
sunny day. The heat absorbed by the pavement actually fries the egg,
not the heat coming down from the sun. When air heats up, its
molecules move farther apart, making it less dense. This air then rises
to higher altitudes where air molecules are less compressed by
gravity. When warm, low-pressure air rises, cool, high-pressure air
seizes the opportunity to move in underneath it. This movement is
called a pressure gradient force.
You never hear about hurricanes hitting Alaska. That's because
hurricanes develop in warm, tropical regions where the water is at
least 80 degrees Fahrenheit (27 degrees Celsius). The storms
also require moist air and converging equatorial winds. Most
Atlantic hurricanes begin off the west coast of Africa, starting as
thunderstorms that move out over the warm, tropical ocean
A hurricane's low-pressure center of relative calm is called
the eye. The area surrounding the eye is called the eye wall,
where the storm's most violent winds occur. The bands of
thunderstorms that circulate outward from the eye are called rain
bands. These storms play a key role in the
evaporation/condensation cycle that feeds the hurricane.
There are five categories of hurricanes, which are based on wind speeds. The categories help
to make people aware of how much damage a hurricane may cause because the greater the
wind speed, the more dangerous the storm.
Category 1 – Winds 74 – 95 mph
Winds snap branches, uproot trees, and overturn mobile homes that aren't secured to the ground.
Category 2 – Winds 96 -110 mph
Winds are strong enough to destroy weak doors and windows, and create 8-foot ocean waves.
Category 3 – Winds 111 - 130 mph
Intense winds cause major flooding near the coast, which can destroy homes and businesses.
Category 4 – Winds 131 - 155 mph
Winds are strong enough to destroy some buildings. Causes heavy damages to building roofs.
Category 5 – Winds greater than 155 mph
Buildings along the shorelines are washed away. Buildings can be completely destroyed.
WHAT’S THE DIFFERENCE BETWEEN A
HURRICANE WARNING AND A HURRICANE
During a hurricane watch, there is the possibility that a
hurricane will make landfall within 36 hours, and people are
advised to prepare for a possible storm ahead. When a
hurricane warning is issued, a hurricane is definitely on the
way, and will make landfall within 24 hours.
The National Hurricane Center, located in Miami, Florida
issues watches and warnings before hurricanes approach
the coastline. They use computers with satellite images to
figure out where and when a hurricane will come on shore.
Sometimes, if a hurricane is strong enough, officials may
require citizens to evacuate, or leave their homes, and travel
to a safer place.