Download What Are Hurricanes

What Are Hurricanes?
Hurricanes are large tropical storms with heavy winds. By definition, they contain winds in
excess of 74 miles per hour (119 km per hour) and large areas of rainfall. In addition, they have
the potential to spawn dangerous tornadoes. The strong winds and excessive rainfall also produce
abnormal rises in sea levels and flooding.
Christopher Columbus was the first European in modern times
to write about the hurricane. The Indians of Guatemala called
the god of stormy weather "Hunrakan." Similar names were
probably present throughout the Caribbean. Captain Fernando
de Oviedo gave storms their modern name when he wrote "So
when the devil wishes to terrify them, he promises them the
'Huracan,' which means 'tempest.'" The same storms in other
parts of the world are known as typhoons, baqulros, Bengal cyclones and willy-willies.
The ocean-water temperature has to be above 79 degrees F in order for a hurricane to be generated, so they
normally form in late summer and early fall when the conditions are right. Meteorologists use the term tropical
storm when a storm's winds are under 74 miles per hour, and hurricane when the wind speed rises. A hurricane
has a peaceful center called the eye, that is often distinctive in satellite images. The eye stretches from 10 to 30
miles wide and often contains calm winds, warm temperatures and clear skies. Around this tropical bliss is a
frenzy of winds gusting at speeds up to 186 miles per hour. If one percent of the energy in one hurricane could be
captured, all the power, fuel, and heating requirements of the United States could be met for an entire year. It
takes 500 trillion horsepower to whirl the great core of winds at such tremendous speeds. It is the equivalent of
exploding an atomic bomb every 10 seconds. (Lockhart, 1988).
How Are Hurricanes Formed?
Left: Image produced by Hasler, Pierce, Palaniappan & Manyin of
NASA's Goddard Laboratory for Atmospheres - Data from NOAA
Hurricanes begin as tropical storms over the warm moist
waters of the Atlantic and Pacific Oceans near the equator.
(Near the Phillippines and the China Sea, hurricanes are called
typhoons.) As the moisture evaporates it rises until enormous
amounts of heated moist air are twisted high in the
atmosphere. The winds begin to circle counterclockwise north
of the equator or clockwise south of the equator. The reatively
peaceful center of the hurricane is called the eye. Around this
center winds move at speeds between 74 and 200 miles per
hour. As long as the hurricane remains over waters of 79F or warmer, it continues to pull
moisture from the surface and grow in size and force. When a hurricane crosses land or cooler
waters, it loses its source of power, and its wind gradually slow until they are no longer of
hurricane force--less than 74 miles per hour.
Hurricanes over the Atlantic often begin near Africa, drift west on the Trade Winds, and veer
north as they meet the prevalling winds coming eastward across North America. Hurricanes over
the Eastern Pacific begin in the warm waters off the Central American and Mexican coasts.
Eastern and Central Pacific storms are called "hurricanes." Storms to the west of the International
Date Line are called "typhoons."
Because of the destructive force of hurricanes during late summer and early autumn, scientists
constantly monitor them with satellites and sometimes even fly airplane surveillance to keep
track of tropical storms that might develop into hurricanes.
Hurricane Intensity & the Saffir-Simpson Scale
Hurricane damage comes not only from wind, but also from rain, tornadoes, floods, and the
effects of very low air pressure. So a system that would rank hurricanes by wind force alone
would not tell the whole tale.
In the 1970s the Saffir-Simpson hurricane intensity category system was developed to
characterize the destructive potential of hurricanes. In addition to maximum sustained wind speed
and central pressure, the Saffir-Simpson hurricane categorization includes storm-surge height and
coastal destruction potential.
The Saffir-Simpson system sets the levels for hurricanes to five intensity categories, described in
this chart under "Damage."
On average, there are about 10 named tropical storms off the east coast of the United States each
year. Of these, 6 are likely to develop into hurricanes, but only 2 to 3 are likely to reach SaffirSimpson category 3 or greater intensity.
Category 5 hurricanes are very rare, occurring about once every one hundred years. Recently,
however, there have been several major hurricane events along the east coast of North America.
In 1988 Jamaica and Mexico's Yucatan Peninsula were ravaged by category 5 Hurricane Gilbert.
In 1989, category 4 Hurricane Hugo landed in Charleston, South Carolina killing 51 people and
causing damage of over $6 billion. On August 21, 1992, tropical storm Andrew strengthened to
hurricane proportions. Reaching category 5, Andrew was one of the most destructive storms ever
recorded along the east coast, destroying more than 63,000 homes, causing $20 billion in
property damage, and killing 27 people. Most of the destructive force from hurricanes is caused
by high winds. Hurricane Andrew was pushed along by winds in excess of 120 mph. In addition,
small whirlwinds were formed near the storm's center, and they picked up speed as they were
pulled inward. These whirlwinds led to gusts of up to 80 mph, giving Andrew a destructive force
of over 200 mph in some areas.
Name: ________________ Class: ________
Part One:
Mark the statements either true or false.
T/F
a. rotates in a clockwise direction in northern hemisphere . . . . . . . . . . . . . . . ___
b. forms over a warm ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .___
c. eye is cloudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
d. eyewall has the strongest winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
e. has wind speeds greater than 74 miles per hour . . . . . . . . . . . . . . . . . . . . . . ___
f. winds move in a counter clockwise direction at sea level . . . . . . . . . . . . . . . ___
g. some form over the Arctic Ocean . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . ___
h. strengthen as they pass over land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
i. form when towering clouds are spun by high level winds . . . . . . .. . . . . . . . . ___
j. form over ocean water at least 79 degrees F . . . . . . . . . . . . . . . . . . . . . . . . ___
k. weaken as they pass over land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
l. contain spiral bands of clouds around the eye . . . . . . . . . . . . . . . . . . . . . . . . ___
m. bring calm weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
n. form when moist air rises above surface . . . . . . . . . . . . . . . . . . .. . . . . . . . . . ___
o. eye is free of clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ___
p. some hurricanes form over the Gulf of Mexico . . . . . . . . . . . . . . . . . . . . . . ___
q. bring heavy rains, lightning, flooding and sometimes tornadoes . . . . . . . . . . ___
r. form over the Atlantic ocean between Africa and South America . . .. . . . . ___
Part Two:
1. Where do Hurricanes Form
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2. How do Hurricanes Form
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3. Describe the Appearance of Hurricanes
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4. What Types of Weather do Hurricanes Bring?
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5. Place
the following developmental stages in order along with their wind speeds :
Tropical Depression, Hurricane, Tropical Disturbance, Tropical Storm
74 or more mph winds; Less than 38 mph;
39–73 mph; very little, if any, organized wind circulation
Stage
Wind Speed (mph)
1.
2.
3.
4.
6. Parts of a hurricane – Match the number from the diagram to the part of the hurricane it represents:
Number
Part
Eye
Eye Wall
Feeder
Bands
Outflow
Description
What goes up must come down, so with the violent rising air converging toward
the storm center at the eye, sinking air develops within. This air dries out, creating
the clear, calm eye. Winds are very light here since the focus of convergence and
hence strong winds are in the eyewall.
A band of clouds, strong winds and heavy rains surrounding the eye of the storm.
At the eyewall, there is rapid movement of air toward the center and upward into
the cloud.
These are squally bands of showers characterized by strong gusty winds and heavy
rains. These bands become more pronounced as the storm intensifies, and are fed
by the warm ocean.
The high level clouds moving clockwise out away from the hurricane at heights of
over 35,000 feet. These clouds are indicative of air spreading out over the top of
the storm, which is essential to its development
7. Hurricane Intensity - The Saffir-Simpson Scale: Fill in the chart.
Category
Wind Speed
(mph)
Air Pressure
(mb or in.)
1
2
3
4
5
©Prepared by Jim Cornish, Gander, Newfoundland, Canada
Based on the Classroom of the Future Webpages
Storm
Surge (feet)
Examples of Damage