Hurricanes are strong atmospheric vortices that are intermediate in
size. The word hurricane comes from a Caribbean word meaning 'big wind'.
Hurricanes originate as tropical disturbances over warm oceans within
tradewinds. The tropical disturbances intensify into tropical depressions,
and then into tropical storms. They originate only in the tropical
tradewinds where ocean temperatures are quite warm. In order for a hurricane
to form the ocean temperature has to be warmer than 26 degrees celcius.
Hurricanes form between 5 degrees and 30 degrees latitude. Hurricanes do not
form within 5 degrees of the equator because of the lack of Coriolis
acceleration. Hurricanes are 250 km in diameter. The average speed of a
hurricane is 20 km/h and the average lifetime is 9 days. Hurricane winds can
reach 120 km/h. Hurricanes need two fuels to get them started and keep them
running. One of these is moist air, the other is heat. Most Atlantic
hurricanes occur in September. Hurricane damage can be very great. In 1942
a hurricane in Bengal, India caused 40,000 deaths. In 1992 Hurricane Andrew
caused $40 billion worth of damage in Florida and the Bahamas. Large
freighters have been washed ashore and planks have been driven through
trunks of palm trees. Hurricanes have caused ocean swells up to 12 meters in
the Bay of Bengal.
Hurricanes can also produce tornadoes. These tornadoes
are weaker than regular tornadoes. Hurricanes loose intensity when they
travel over land. That is why only the coastal areas receive hurricane
damage. The eye is the low pressure region in the center of the hurricane.
The eye of the hurricane is 40 km in diameter. The lowest hurricane
pressure ever recorded was that of Hurricane Ida in 1958. The pressure level
was 877 mb. Hurricanes are given names by meterologists, for example
'Hurricane Gloria' or 'Hurricane Hugo'. An alphabetical list of names is
drawn up for that year's hurricanes.