Download Ten Worst Hurricanes

Resource Card: Tornado
Overview
The word "tornado" comes from the Latin tonare, meaning "to thunder." The Spanish developed the word into tornear, to
turn or twist. These are good descriptions of tornadoes, which are formed by rotating or twisting air. This is why they are
also called twisters or cyclones.
A tornado is a powerful column of winds spiraling around a center of low atmospheric pressure. It looks like a large black
funnel hanging down from a storm cloud. The narrow end will move over the earth, whipping back and forth like a tail.
The winds inside a tornado spiral upward and inward with a lot of speed and power. It creates an internal vacuum that
then sucks up anything it passes over. When the funnel touches a structure, the fierce winds have the ability to tear it
apart.
The winds inside a twister can spin around at speeds up to 500 miles an hour, but usually travels at roughly 300 miles an
hour. This makes the tornado the most dangerous storm known to mankind. Because of the earth’s unique weather
system, twisters rotate counterclockwise in the Northern Hemisphere and move eastward. They rotate clockwise in the
Southern Hemisphere. Tornadoes also often come with hailstorms.
Many storms create harmless funnels that never touch earth. They can last from a few seconds to a few hours. Others
disappear and reappear minutes later. The average tornado has a diameter of about 200 to 300 yards, and some grow
large enough to spawn smaller tornadoes known as satellite tornadoes. These small offspring, about 50 yards across, can
be very fierce and do lots of damage. They also tend to branch away from the parent funnel, taking separate paths across
the earth.
Causes of Tornadoes
A tornado can form very quickly, sometimes in a minute or less. It can travel across the ground at high speeds, then just as
suddenly vanish. They can kill in a matter of seconds. Every year, about $500 million worth in damage is done by twisters
in the United States. Most tornadoes last less than twenty minutes and travel less than 15 miles. However, superstorms
sometimes occur, traveling over 100 miles before they are exhausted. Although they don’t occur very often, they are
responsible for 20% of all tornado casualties.
Tornado conditions are caused when different temperatures and humidity meet to form thunderclouds. In the United
States, warm, wet winds from the Gulf of Mexico move northward in spring and summer, meeting colder, dry Canadian
winds moving southward. The place where these two winds meet is called a dry line. High, dry air coming from the north
piles on top of low-moving, moist Gulf air at a height of over 10,000 feet. The warm southern winds try to rise, but the cold
northern air blocks them. This clash causes the warm, trapped air to rotate horizontally between the two air masses. At the
same time, the sun heats the earth below, warming more air that continues to try and rise. Finally, the rising warm wind
become strong enough to force itself up through the colder air layer.
When this occurs, the cold air on top begins to sink, sending the rising warm wind spinning upward. The warm winds
rotate faster and faster in a high column. When the updraft is strong, the column can rise to heights of 10 miles or more,
twisting at speeds of up to 100 miles an hour. The rotating winds produce strong storm clouds about 70,000 feet high,
sometimes spreading 10 miles wide.
This storm system may stay intact for several hours, at which point its thunderclouds are known as supercells. These
storm clouds can send down an inch of rain in a mere ten minutes or shower the ground with baseball-sized hailstones.
Supercells can accumulate into huge clusters, forming a line almost 100 miles long, which can then develop into
mesocyclones.
Types of Tornadoes
Just as earthquakes are rated on the Richter scale, tornadoes are rated on a scale from F-0 to F-5. F-0 and F-1 storms can
collapse chimneys and toss mobile homes off their foundations. They have the strength to push cars off roads. F-2 and F-3
tornadoes can tear away roofs and lift and toss heavy cars.
F-4 and F-5 tornadoes are so strong they can pick up and carry entire buildings a distance, toss steel beams, and crunch
cars. F-4 and F-5 tornadoes are rarer, but are responsible for 2/3 of the 120 or so tornado deaths in the United States
every year.
Ten Worst Tornadoes
Date
Location
Dead
1925, March 18
Midwestern United States
689
1884, February 9-19
Southern United States
Over 600
1936, April 5-6
Mississippi and Georgia
419
1896, Mary 27
St. Louis, Missouri
Up to 400
1952, March 21-22
South-central United States
343
1974, April 3-4
Midwestern United States
315
1840, May 7
Natchez, Mississippi
Over 300
1965, April 11
Midwestern United States
272
1932, March 21
Alabama
268
1917, March 23-27
Midwestern United States
211
Resource Card: Hurricane
Overview
There has been a hurricane in every year in the last five centuries. And each year has borne witness to at least one great
hurricane. These huge storms begin in the tropics, over the oceans. When they form in the Atlantic Ocean, the Caribbean
Sea, or west of the international dateline in the Pacific Ocean, they are known as hurricanes, a Carib Indian word meaning
“big wind.” When they begin east of the international dateline, they are called typhoons, from the Chinese for “great wind.”
In the Indian Ocean, these storms are referred to as cyclones, based on the Greek word for “coil.” Locals also give these
storms different names. In Australia, for example, residents call them willy-willies.
In tropical waters like the Gulf of Mexico and the Caribbean Sea, storms usually form in May and June. In the Atlantic
Ocean, they usually form from July to October, often beginning off Africa’s west coast. The squalls build in power as they
drift west.
There are about 100 storms spotted each year that could develop hurricane strength, about 10 of which become tropical
storms. Only about 6 grow into full-force hurricanes, and only 2 strike the United States every year.
Hurricanes tend to travel in a northwest direction, but turn northeast after hitting land. Their path usually cuts from the
equator to as far north as Canada, often covering thousands of miles over land and sea. The average hurricane lasts about
nine days, towering ten miles high, with the most force during the storm’s first 12 hours onshore.
Once more modern hurricane tracking systems began, scientists found it necessary to identify each storm. Beginning in
1953, the first storm of the season was given a woman’s name starting with the letter A. The second storm was a woman’s
name beginning with the letter B, and so on. It wasn’t until 1979 that men’s names began to be used.
Every six years, the names repeat. However, if the storm was particularly violent or destructive, the name is taken off the
list. That way, when someone mentions Hurricane Camille, most people know they mean the storm that hit the Mississippi
Delta in 1969.
Sometimes, names are specially changed to suit the area of the world that is hit. When hurricanes approach within 1,000
miles of Hawaii, for example, they are given Hawaiian names.
Causes of Hurricanes
Hurricanes can develop when the sun’s rays heat tropical waters to at least 82 degrees Fahrenheit. This causes the air to
grow warmer and rise. Water rises with it as vapor, and the heat causes the air to rise faster and faster. In about 12 hours,
the heated air will begin to circle counterclockwise, forming stronger and stronger winds that whirl with increasing speed.
Air that is motionless is calm. When it moves slowly, it is a light breeze. If it moves slightly faster, it becomes a fresh
breeze, and even faster is a high wind. A wind becomes a hurricane when it reaches speeds of more than 74 miles (120
km) per hour. It is unknown what top hurricane speeds are, because instruments have always been destroyed by high
winds or flying debris. Some estimate that hurricane winds do not surpass 250 miles (400 km) per hour, while others say
they can reach 600 miles (960 km) per hour.
The moist, hot winds of a hurricane swirl upward around a calm column of low-pressure air known as the eye. Some
hurricanes can develop more than one eye, but the largest is always the main eye and measures an average of 15 miles
across. Inside the eye there are no storm clouds, almost no wind, and calm conditions. However, beneath this tranquil
center is wild, stormy chaos.
The rising winds rotate in increasingly tight spirals around the eye, rising faster and faster. Cooler air is also sucked in,
heated, and sent twisting up the eye. When the hot air rises high enough, it cools and forms water droplets that cluster
together as clouds and drop rain. The rain is blown around by fierce winds.
Hurricanes were once thought to be shaped like doughnuts, circling around the eye. However, satellite images have shown
them more to resemble pinwheels, with thicker clouds near the center and long, thin, trailing ends.
The atmospheric pressure is lowest closest to the eye, making the winds there spin faster. At the storm’s outer edges, they
blow more slowly. A hurricane moves west or northwest at an average of ten miles an hour, with a wind radius as large as
100 miles. As it moves, it churns up the sea beneath the eye, sucking ocean water up and creating huge ocean waves. The
raised water is carried along by the storm to the shore.
Types of Hurricanes
The National Oceanic and Atmospheric Administration (NOAA) divides hurricanes into five categories in a warning
system. Category 1 hurricanes are small and have winds of 74 to 95 miles per hour. They create 4 to 5-foot-high waves.
Category 5 hurricanes, on the other hand, have winds racing over 155 miles per hour, carrying waves higher than 18 feet.
These usually cause the most damage.
A hurricane with 150-mile-an-hour winds can put 11 tons of pressure against anything it hits. If a house is poorly built, it
can be smashed, torn, or lifted off its foundation. Cars are often swept away in flash floods or blown over by fierce winds.
Ocean waves can tower to enormous heights, taking boats and beach houses back to sea.
Ten Worst Hurricanes
Date
Location
Dead
1970, November 13
East Pakistan (Bangladesh)
500,000 to 1 million
1737, October 7
Bengal, India
Over 300,000
1881
Haiphong, Vietnam
300,000
1876
Bengal, India
200,000
1882, June 6
Bombay, India
Over 100,000
1864, October 5
Calcutta, India
50,000 to 70,000
1965, May and June
East Pakistan (Bangladesh)
35,000 to 40,000
1942, October 16
Bengal, India
Over 35,000
1963, May 28-29
East Pakistan (Bangladesh)
22,000
1780, October 10-12
Caribbean Islands
20,000 to 30,000
Resource Card: Drought
Overview
A drought occurs when there is not enough rain to support people or crops. In temperate regions, a drought is classified as
15 consecutive days with less than 0.01 inches (0.25 millimeters) of rain. During a drought, it still rains once in a while.
However, storms or cloudbursts are brief and any precipitation that falls dries up quickly afterwards. Small droughts occur
every now and then, and these are not particularly harmful. Most happen in the summer, when hot and dry weather is
normal. However, sometimes droughts can occur of months, years, or even decades. When an area appears to suffer from
dryness for thousands of years, the region is said to have a dry climate.
When there is a dry spell, grass begins to turn brown. Flowers need to be watered more frequently. Dirt patches dry up.
Cracks form across the surface of the ground. After many weeks of such weather, plants die out. The roots of the plants,
which previously anchored soil down, can no longer keep the soil from eroding. The dirt is then blown up by the wind,
causing huge clouds known as dust storms. Because they can turn the sky dark, they are sometimes known as black
blizzards.
Causes of Droughts
We already know that a drought occurs when not enough rain falls to the ground. However, water vapor condenses only if
air rises into the colder regions of the atmosphere. If the air doesn’t rise, then no rain will form. When there is high air
pressure, air falls instead of rising. With the air pressing down in a high pressure zone, no currents of water vapor are
carried upward. As a result, no condensation occurs, and little rain falls to earth. In addition, high-pressure areas push
clouds and air currents downward and away, resulting in sunny, cloudless weather. Low-pressure systems see more
cloudy, stormy weather.
Usually, however, we experience both high- and low-pressure systems. It is normal for a high-pressure system to pass over
an area and move on, being replaced by a low-pressure system. However, when a high-pressure system is stalled, the
sunny weather can drag on for days. If it keeps on going, the result is a drought.
High-pressure systems can be stalled by jet streams, wide bands of fast-moving air (up to 335 miles per hour) in the upper
atmosphere. Masses of air that usually move from place to place can be locked in one area by jet streams.
Unusual currents of cold and warm water in the ocean can also stall a high-pressure system. In the Pacific, a warm water
current known as El Nino brings low-pressure systems that cause hurricanes and other violent storms to North America,
while a cold water current known as La Nina brings drought. In Asia, the opposite occurs, with El Nino bringing drought
and La Nina stormy weather.
Or droughts occur because water vapor is not brought by air currents to the right areas at the right times. Water that
evaporates from the oceans is brought inland by wind to regions where it is needed. However, sometimes those winds are
not strong enough. In the eastern United States, moisture is carried up from the Gulf of Mexico by northward blowing
winds. This moisture is then pushed by other winds until it reaches the Midwest. This water then falls to the ground,
supporting the farms in that region. However, if the winds don’t blow at the right time, in the right direction, or with
enough force, the moisture falls in other areas and that Midwest region suffers from drought. A similar phenomenon
occurs in southeast Asia. Usually, summer winds known as monsoons carry water vapor north from the Indian Ocean
inland, providing desperately needed rain. Sometimes, however, instead of blowing from north to south, they blow east to
west. When that happens, the vapor doesn’t leave the Indian Ocean and many people suffer from the resulting droughts.
Mountains can prevent wind from blowing moisture to needed regions. As air is moving past a mountain range, it is forced
to rise in order to pass over the peaks. However, as the air rises, it becomes colder and the vapor condenses into rain or
snow. The rain then falls on that side of the mountain, known as the windward side (the side that is turned toward the
wind). When the air mass finally makes it over the mountain, it has lost much of its vapor. This is another reason why
many deserts are found on the side of a mountain facing away from the ocean. This phenomenon is known as the rain
shadow effect.
Case Study 1: Midwestern United States (1932-37)
This devastating drought was caused by overuse and abuse of the American prairie lands. Before settlement, natural deeprooted grasses could survive drought periods. But after people began moving westward, these grasses were plowed under
to raise crops or overgrazed by free cattle. The soil was exposed to the prairie winds, which soon blew away the rich
topsoil. Overproduction of wheat in 1931 caused a drop in prices. Economic depression, a late freeze, violent storms, insect
plagues, and drought affected about 50 million acres of the Great Plains region. The first “black blizzards,” or dust storms,
began in November 1933. Dust particles blocked out the sun for days at a time, forcing people to use indoor lights
throughout the day. Dirt blew under windowsill and through door jambs, settling on everything, including food, water,
and machinery. Farm wives tried stuffing rags into cracks to block out the dust. The drought continued for the next two
years with no relief, and the affected area expanded north and eastward. Dust storms continued to blow. Dust particles
were carried as far east as New York City and on ships at sea. About 350 million tons of soil was carried into the air and
blown away. In the affected area, livestock died of suffocation and starvation while crops grew stunted and grow. Black
drifts formed around homesteads, blocking highways and railroad lines. Airports were closed due to reduced visibility.
Sand and silt scrubbed the paint off houses and automobiles. They also created huge electrical storms that had no rain. As
many as a hundred separate dust storms were recorded in a single year in parts of Texas and Oklahoma. Hundreds died
from respiratory problems, and thousands more migrated and abandoned their farms. In 1936, Congress passed the Soil
Conservation Act, which allocated $500 million to relieve those farmers who started planting soil-building crops. This
program helped stop overproduction of crops and the grain surpluses that were being depleted by the long drought. Largescale agricultural and conservation education programs were created along with “shelter belts,” rows of trees planted as
windbreaks. The drought finally ended by 1937. Good weather returned with rising post-Depression prices. The weather
remained good and large crop harvests continued through the crucial World War II years that followed.
Case Study 2: The Sahel, Central Africa (1965 to present)
Hundreds of thousands (and possibly millions) of people have died as a result of the extended drought throughout the
huge semi-arid transition zone between the Sahara Desert and Equatorial Africa. Nomadic herdsmen have suffered
famine, starvation, dislocation, and political strife as a result of the drought. Some 200,000 have died in Ethiopia, along
with countless cattle. This, together with government inaction, led to an army rebellion against Emperor Haile Selassie.
The streets of Timbuktu were swept full of sand. Many desert tribes, like the Tuaregs now found their lives changed
forever. The drought is thought to represent evidence of a general global cooling off, a major climatic cycle change that
could affect the entire world. Other meteorologists think the drought is only a local phenomenon caused by land overusage. According to this hypothesis, the drought was caused by cattle and goat herds, which stripped away plants and
increasing ground reflectivity. This caused more sunlight to be radiated into space. This atmospheric reheating produced
dry, hot air layers above the ground, drying it out and discouraging rain cloud formation. Ironically, these large herds were
made possible by a deep-water well network drilled by several Western countries to help the native people become selfsufficient.
Resource Card: Monsoons
Overview
Monsoons are cyclical wave-like air masses that occur in the sub-tropics, moving onto land from the sea during the
summer and returning over water in winter. The word monsoon comes from the Arabic mausim, meaning “season,”
because these storms return year after year. For many countries along the Indian Ocean and South Atlantic, the yearly
monsoon rains are essential for crops. However, although these storms will bring much needed water, they can also cause
severe flooding, damage, and famine.
Causes of Monsoons
Monsoons are an annually recurring weather phenomenon, triggered by the earth’s tilt in relation to the sun. Although
they return every year, it is still impossible to tell the timing, duration, and quantity of rain each season, a fact that leaves
impacted areas without accurate storm information. Monsoons are set by land and sea temperature differences. Land
reflects the sun’s rays, heating air over land more rapidly. Water is able to absorb a lot of heat without itself changing
temperature much, so air over water stays relatively cooler.
This fact is prevalent in Asia because the northern hemisphere has so much more land than the southern hemisphere,
which is mostly ocean. During he summer, the earth is tilted at such an angle that the sun’s rays shine more directly on the
northern hemisphere. The heat is absorbed by the land masses, warming the air above it. The hot air rises, and cooler
ocean air rushes inland from the southern hemisphere to replace it. As it moves, it carries moisture with it, releasing it
over land as the summer monsoon (also known as southwest monsoon). The cycle continues as the cooling air creates
precipitation and releases more energy. This energy then heats the air, which rises and flows back to the sea, cools,
descends, and rushes back to land to replace more warm, rising air. This monsoon is centered over continental Asia.
There is also a winter monsoon (also known as northeast monsoon), created during the winter when most of the sun’s rays
shine on the southern hemisphere. During this season, the continents are cooler than the water, which retains absorbed
heat. The air reverses circulation, with warm air rising over the oceans and cooler land air, called “cold surges,” rushing in
to replace it. The cold surges pick up warm moisture as it travels across tropical waters only to release them over
Indonesia, northern Australia, Sri Lanka, and the east Indian coast.
Current Event: India Monsoon of 2007
NEW DELHI, India, July 5, 2007 (ENS) - Over the past month, more than 1.5 million people have been affected by
storms, tornados and landslides in Bangladesh, in what has been described as the worst monsoon season in 25 years.
Heavy monsoon rains also are making life miserable for people in Afghanistan, Pakistan, and India.
Eighty four people in the Indian state of Gujarat have lost their lives ever since torrential rains hit on Monday. Some
43,000 people have been evacuated from their homes as houses collapsed and crops were inundated.
The South Africa-based charity ActionAid says heavy rains in the state of Maharashtra this week killed more than 50
people and have left thousands homeless.
The Indian meteorological department forecasts more heavy rainfall in both Maharashtra and Gujarat.
The Maharashtra capital city of Mumbai is limping back to normalcy
after heavy downpours last week. Five persons were killed when a
building collapsed and two people were electrocuted.
In the rural Amravati district, 350 villages are underwater and the
rains have claimed the lives of 26 people.
Power supply and roads have been badly hit, while thousands of
people have been evacuated from their homes. Efforts to find missing
persons are still ongoing.
"Crops and almost three feet high soil have been washed off from
farms. This means that farmers can resume agricultural work only
after four months. Some land in fact has been rendered barren," says
Flooded vehicles on a Mumbai road. (Photo Dr. Madhukar Namdev Rao Gumble of Apeksha Society, an
courtesy State of Maharashtra)
ActionAid partner organization.
People are in desperate need of clothes, bedding and blankets. Plastic sheets and bamboo poles are also needed to make
temporary houses, he said.
Water from the Amravati district's Vishroi dam was released,
flooding the Pedhi River, which rose so high that some villages are
standing in eight feet of water.
Low-lying areas, which mostly house minority Dalit families, have
borne the brunt of flooding.
Forty-one people in Andhra Pradesh have lost their lives in recent
days and more than 300,000 people in 220 villages have been badly
hit. An estimated 10,000 houses are damaged and 27,000 acres of
land affected.
ActionAid teams trying to reach affected Andhra Pradesh villages
found their way blocked by washed out roads and bridges.
Rahamad Bee, a 30 year old Muslim woman was distraught. "I need
to earn money. I need to cook. I need to take care of the family. How
can I do this when the house is gone?" she implored ActionAid staff.
This home in Amravati was utterly
destroyed. (Photo courtesy ActionAid)
"Water logging, silt deposit and consuming wet grain are likely to cause further illness. These villages urgently need safe
drinking water and medical assistance," says Sandhya Srinivasan, head of ActionAid's Andhra Pradesh team.
Promises by Andhra Pradesh Chief Minister to provide Rs 4,000 to those whose homes were washed away and Rs 2000
for submerged houses were greeted by protests. Communities say it will cost them Rs 12-15,000 to rebuild their houses,
particularly as they should be more, not less secure than ones they have lost.