There are many different names tropical
storms such as cyclone and typhoon.
However, the storm is named by the
location of its formation. Hurricanes start
in the Atlantic, off the west coast of Africa.
An average of around a dozen hurricanes
form in the Atlantic each year. The
hurricanes then travel westwards towards
the Caribbean, the east coast of Central
America and southern USA. Hurricanes
can last as long as a month and although
they travel slowly at around 15 mph wind
speeds can reach over 75 mph.
There are many factors which cumulate to form a hurricane.
Hurricanes form in tropical areas 23.5°North or South of the
equator. They also need a sea with a depth of over 60m. Rising
warm air triggers a decrease in pressure at higher altitudes.
Warm air is under a higher pressure than cold air, so moves
towards the area taken up by the colder, lower pressure air. The
low pressure sucks in this warm air which then also rises. A
continuous upflow of warm and wet air continues which leads to
the creation of clouds and rain.
Air surrounding the low pressure zone at
the centre flows in a spiral. It flows anti-
clockwise in the northern hemisphere and
clockwise in the southern hemisphere at
speeds of around 75 mph. Air is ejected
from the top of the storm, which can be
around 15km high, and this air falls to the
side of the storm away from the eye. As this
process happens, it reduces the mass of air
above the storms eye which causes wind
speed to increase further. Not all of the
ejected air moves away from the eye of the
storm. Some cools and dries, sinking
through the eye, increasing the low
pressure at the centre.
As the winds pick up speed, the air pressure in the centre
lowers, and the cycle continues. The hurricane will only grow in
strength. As often seen from above, hurricanes are huge circular
bodies of thick cloud, measuring around 300 miles wide. The
cloud brings heavy rain, thunder and lightning.
6. End of the cycle
The centre of the hurricane is known as the eye, and it measures
about 30 miles across. Often there are no clouds in the eye.
From below it seems calmer, with a circle of blue sky visible
above. The eye is formed because as it is the only area of the
hurricane where cold air is descending. In the northern
hemisphere, the prevailing easterly winds often steer hurricanes
toward land. Despite this, a hurricanes course is often
unpredictable. As hurricanes move inshore, their power reduces
because their energy comes from sucking up moist sea air.