Hurricanes
Directions:
Use the information in this packet to answer the
questions about hurricanes.
Hurricanes
are powerful, rotating storms that form near the equator. This
means they form in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in
the eastern Pacific Ocean. Hurricanes gather heat and energy through contact with
warm ocean waters and the evaporation of seawater increases their power as they
continue to move across an ocean or large body of water. Hurricanes are associated
with a huge amount of rain, low air pressure, thunder and lightning, and flooding.
Hurricanes rotate in a counter-clockwise direction around an "eye" and have
winds of at least 74 miles per hour. When they move onto land they bring heavy rain,
strong winds and large waves that can damage buildings, trees and cars. The term
storm surge is used to refer to the large waves that can hit the shore and often cause
large amounts if damage. Storm surges are very dangerous and a major reason why you
MUST stay away from the ocean during a hurricane warning or hurricane. Typhoons
are a special name just for hurricanes that form in the western Pacific Ocean.
Generally, when a hurricane moves over land (or over cold ocean waters) the
storm begins to weaken and quickly loses strength because the storm is fueled by warm
water. On average, there are about 100 tropical cyclones worldwide each year. In
general, 12 of these will form in the Atlantic Ocean, 15 will form in the eastern Pacific
Ocean, and the rest are in other areas around the world.
Hurricane season is the time when most Atlantic Ocean hurricanes occur and
it is from June 1 until November 30. In the eastern Pacific Ocean, hurricane season is
from May 15 until November 30.
How Hurricanes Form and Die
Requirements for a Hurricane:
Hurricane
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An area of low pressure
Deep (150ft), warm (>79°) ocean water
Moist air above the ocean
Tropical winds (near the equator).
Stages in Hurricane Development:
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3
2
1
1. A tropical disturbance is an area of organized thunderstorms that form in the
tropics or subtropics and are strong enough to persist for at least 24 hours. They
are usually between 200 and 600 miles in diameter, move from east to west,
and represent an area of low pressure.
2. Once a tropical disturbance has maintained a sustained surface wind of at least
30 mph is has become a tropical depression. At this point the storm system
becomes more organized and exhibits a tighter circulation pattern. As the warm,
moist air over the ocean rises due to low air pressure cold air moves in to replace
it. This produces strong gusty winds, heavy rain and tall cumulonimbus clouds
(thunderclouds).
3. At the point where the maximum sustained surface winds reach between 39-73
mph it is designated as a tropical storm and is given a name.
4. When the maximum sustained winds surface winds are greater than 74 mph the
center of low pressure is now called a hurricane and at this stage the a well
developed eye can be seen on radar and satellite images.
Hurricanes form in the tropics, over warm ocean water (over 79º) and at north
and south latitudes between 8° and 20°. These powerful storms are fueled by the heat
energy that is released when water vapor in the atmosphere condenses to form liquid
water (latent heat of condensation). The hurricanes that affect the east and southeast
portions of the United States form off the coast of Africa and move west over the
Atlantic Ocean. They generally make their appearance later in the season (August and
September) because at the beginning of hurricane season the water off the coast of
Africa is still too cold to support the formation of a tropical disturbance.
The End of a Hurricane:
When a hurricane travels over land or cold water it will begin to weaken, quickly
becoming a tropical storm once more. This occurs because the evaporation that is
needs to fuel the storm is no longer available once the hurricane is removed from the
warm, moist air that it depends on.
The History of Hurricanes
Scientists have only been studying hurricanes only for about 100 years though
there is evidence that they have been occurring for much longer than that. Geologists
have studied layers of sediment in a lake in Alabama and believe that the sediment was
brought there by a hurricane in the Gulf of Mexico that took place over 3,000 years ago.
Evidence has also been found in Florida that provides evidence of a hurricane that took
place more than 1,000 years ago.
One of the first human records of hurricanes appears in Mayan hieroglyphics. The
Mayans seemed to use the knowledge that they gained to take precautions against
hurricanes by building their major settlements away from the hurricane-prone coastline.
In fact, it is the Mayan word "Hurakan" that became our word for "hurricane." Hurakan
was the name of a god who blew his breath across the water and brought forth dry
land. Later in history the Carib Indians gave the name "Hurican" to one of their gods of
evil.
Many storms left
left important marks on history:
• 1565: A hurricane scattered a French fleet of war ships and allowed the Spanish
to capture a French fort in what is now Florida.
• 1609: A fleet of ships carrying settlers from England to Virginia was struck by a
hurricane. Some of the ships were damaged and part of the fleet was grounded
on Bermuda (an island nation in the Atlantic). These passengers became the first
people to live in Bermuda.
• 1640: A hurricane partially destroyed a large Dutch fleet that was poised to attack
Cuba.
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1800s & 1900s: In 1893 hurricanes hit Louisiana, South Carolina and Georgia and
killed as many as 4,000 people while in 1900, a Texas hurricane killed more than
8,000 people and would be rated as a Category 4 storm on the present day
scale.
As the ability to forecast a hurricane improved, communities were no longer taken
by surprise and could take measures to evacuate ahead of the storm. While destruction
still continues, the number of deaths due to hurricanes has dropped significantly.
Why Can't We Stop Hurricanes?
One of the most commonly asked questions is why we don't try to stop
hurricanes from forming or to disrupt them once they do form. It doesn't sound too hard,
does it? Unfortunately researchers have found it's nearly impossible to do and/or may
require technology that we do not currently have. The federal government, through the
National Oceanic and Atmospheric Administration (NOAA) tried various inventions (like
cooling the ocean water, or adding chemicals to a hurricane) in the hopes of weakening
a hurricane but they gave up in the 1960s. The weather systems that make up
hurricanes are too large and too powerful to stop so now NOAA researchers focus on
trying to better understand how hurricanes form and move.
In 1955, Congress funded the National Hurricane Research Project to conduct
research into these dangerous storm systems. In 1960 the researchers associated with
the project acquired two DC6 airplanes to use solely for hurricane research. Due to the
improvement of computers and the regular flights of the "Hurricane Hunter" planes
meteorologists have been able to learn more and more about hurricanes. Over time, the
forecasts and projected track of a hurricane has become increasingly accurate and
helpful to people in areas that could be affected by the storm.
Hurricane Tracking
The National Hurricane Center, which is part of the National Weather Service and
the NOAA, is responsible for tracking tropical storms and hurricanes. Hurricane watches
and warnings are issued when a storm gets close to the U.S. and anyone can track the
progress of a storm by listening to the coordinates given by your television
meteorologists. Another option available for anyone to use is the website
http://www.nhc.noaa.gov/. This website will show you the latest longitude and latitude
locations detected and predicted by the National Hurricane Center.
• Hurricane Watch: A hurricane is possible within 36 hours and the Hurricane Center is
tracking the storm and trying to predict where it might make landfall. At this point you
should stay tuned to the radio and television for more information.
• Hurricane Warning: A hurricane is expected within 24 hours and at this point you should
begin preparing to evacuate in case it is determined that this is the best course of
action to keep you safe.
The path of a storm is tracked using satellites that can produce a variety of
images that can be extremely useful to a meteorologist. These images can include radar
and water vapor which can help determine the strength and intensity of the storm. A
hurricane is often plotted on a tracking map using the latitude and longitude of the eye of
the hurricane as it moves from east to west. An example of a hurricane’s coordinates
might look like 20ºN, 75ºW. The first coordinate is always the current latitude of the
storm and the second coordinate is always the current longitude.
Tropical Storm
Hurricane
Meteorologists track hurricanes on a specific type of map called a tracking map.
This type of map is a representation of the Atlantic Ocean and Gulf of Mexico which
allows meteorologists to track the progression of a hurricane and predict where it might
make landfall. The exact location of a hurricane can be tracked easily but the direction it
will move, its speed, and how the intensity of the storm may change can be much
harder to predict with any measure of accuracy. Often times a weather forecast will
warn people of the possible tracks that a hurricane may take so they can be prepared if
it does make landfall in their area.
Hurricane Structure
Since a hurricane is a center of low pressure the winds blow counterclockwise and
spiral in towards around the center of the storm which is called the eye. The eye of a
hurricane is approximately 20 to 30 miles wide and represents the calmest, warmest,
and driest part of a hurricane. The rotational direction of a hurricane determines where
the strongest winds, and therefore the strongest storm surge, will make landfall. If you
are standing on the beach and facing an incoming hurricane (which is something you
should NOT do in real life), the strongest winds will be on the side of the hurricane that is
to your left. These stronger winds are created by the counterclockwise rotation of the
storm and will push very strongly on any water that is coming into the shore (storm
surge).
Surrounding the eye is something meteorologists refer to as the eyewall. The
eyewall is basically a wall of thunderclouds and it is the part of hurricane that tends to
cause the most damage when it passes directly over a location. When the eyewall
passes over an area it brings the heaviest rains and the strongest winds, which can
gust to 225 mph in a strong hurricane. The general rule is; the smaller the eye, the
stronger the winds. The long bands of rain clouds that appear to spiral in towards the
eyewall are called rainbands. The number and size of the rainbands depends on the
size and strength of the hurricane. They travel relatively slow, only about 20-25 mph,
as they move across a large body of water and make there way onto land.
Hurricane Landfall and Storm Surges
When a hurricane reaches the land meteorologists report that the hurricane has
made landfall. When hurricanes make landfall they bring with them large amounts of
rain, strong winds, and possibly tornadoes.
When the oceans rises as a result of strong winds from a hurricane or other
intense storm this phenomena is referred to as storm surge. This rise in ocean water
causes large waves that can crash onto the shore causing flooding and large amounts
of damage. When the storm surge is combined with the large amounts of rainfall the
flooding that can result is one of the most dangerous aspects of a hurricane that makes
landfall. This is especially true when a hurricane makes landfall in highly populated or low
lying coastal area which is already prone to flooding. The height of the storm surge is the
difference between the current level of the ocean and the level that the ocean would be
under normal conditions. It can be estimated by subtracting the regular tide level at the
time of landfall from the observed tide as the storm moves onto land.
Hurricane Classification
The Saffir-Simpson scale rates a hurricane based solely on its current wind speed and is
used to give an estimate of the potential property damage and flooding that could be
associated with it when it makes landfalls.
SaffirSaffir - Simpson Scale
Category
Wind Speed (mph)
Storm Surge (ft)
1
74 to 95
4 to 5
2
96 to 110
6 to 8
3
111 to 130
9 to 12
4
131 to 155
13 to 18
5
155 and greater
18 or greater
A History of Big Hurricanes
• Hurricane Carla,
Carla , September 10, 1961:
1961 This hurricane struck the Texas coast
causing about 500,000 people to be evacuated from the area. Winds near the
center of the hurricane were estimated at 150 miles per hour, the storm caused
billions of dollars in damage, and 46 people died.
• Hurricane Betsy,
Betsy, September 8, 1965:
1965 This hurricane hit Florida first before turning
towards the Louisiana coast. A total of 75 people lost their lives and winds were
estimated to be as high as 160 miles per hour.
• Hurricane Camille August 17, 1969:
1969 This hurricane was a Category 5 hurricane,
which is the most powerful rating, and had winds as high as 200 miles per hour.
The hurricane hit along the US Gulf Coast but also caused flooding in Virginia and
the death of 250 people.
• Hurricane Celia,
Celia , August 3, 1970:
1970 This hurricane hit Texas and contained very
high winds that damaged an airport and demolished a nearby mobile home park.
Fortunately only 11 people lost their lives that day.
• Hurricane Gilbert,
Gilbert, September 16, 1988:
1988 This hurricane was a Category 5
hurricane with winds as high as 160 miles per hour. It went through Jamaica, over
the Yucatan peninsula of Mexico, and finally made landfall in the U.S. (Texas and
Oklahoma) as a heavy rain storm. It caused billions of dollars worth of damage in
Mexico and 318 people lost their lives.
• Hurricane Andrew,
Andrew, August 24, 1992:
1992 This hurricane hit southern Florida before
turning towards Louisiana. More than a million people had to leave the area due
to the storm which brought heavy rains and tornadoes. Until Katrina, Andrew
was the most expensive hurricane in the history of the U.S.
• Hurricane Floyd,
Floyd, September 1999:
1999 This hurricane brought so much rain that 13
states were declared disaster areas by the federal government. At the time this
was the largest declaration for a single event than ever before in the history of the
United States. More than $500 million of federal money was spent on helping
states recover. North Carolina was hit the hardest of any state.
• Hurricane Katrina,
Katrina , August 2005:
2005 This hurricane was the most destructive and
expensive natural disaster in U.S. history. The damage caused has been
estimated at $81 billion in the New Orleans area and along the Mississippi coast.
Katrina was responsible for approximately 1,200 reported deaths, including about
1,000 in Louisiana, 200 in Mississippi and 7 in southern Florida.
• Hurricane Rita,
Rita , 2005:
2005 This was the third category 5 hurricane of the 2005
season and devastated portions of southeastern Texas, southwestern Louisiana,
and the Florida Keys. Hurricane Rita was responsible for 7 deaths and caused an
estimated $10 billion in damages in the United States.
Naming Hurricanes:
Since more than one tropical storm or hurricane can exist in the same area at the
same time meteorologists give each one a different name to prevent confusion. The first
tropical storm of the year is given a name that starts with ‘A’, the second storm of the
year is given a name that starts with a ‘B’, and this pattern continues in order through
the rest of the alphabet. The only exceptions in the order are made for the letters Q, U,
X, Y, and Z because there are not many common names that start with those letters.
Meteorologists also alternate between men’s names and women’s names using lists
generated by the World Meteorological Organization.
The World Meteorological Organization created 6 lists different lists of names that
are used over and over again. The exception to this rule occurs when a hurricane is
particularly destructive and results in the name being retired so that it can never be used
again. One of the most active hurricane seasons on record took place in 2005 and
forced meteorologists to get creative. When all of the letters of the alphabet had been
used they began naming each new storm using Greek letters. In the table below you
can see the order of the lists as they were used from 2004 to 2009.
Hurricane Katrina (2005):
The storm surge that was associated with hurricane Katrina was as low as 4.1
feet in some areas and as high as 27 feet in other areas. As mentioned earlier, the
flooding that is associated with hurricanes can be deadly, and in the case of hurricane
Katrina it resulted in the deaths of 240 people. New Orleans was a low lying area that
had relied on levees to protect the city from flooding in the past. Sadly, the levee system
that the city was relying on failed in the face of what the hurricane was throwing at
them which caused an additional 1500 deaths and another 81 billion dollars in damages.
The flooding of New Orleans can be attributed to some of the items listed below.
1. The size and intensity of the storm surge
2. Approximately 80% of New Orleans lies below sea level
3. The large amounts of rain that were produced when the hurricane made landfall
4. The pumps that were designed to help in times of large amounts of rainfall were
not able to handle the large amounts of water that Katrina was bringing into the
city
5. The levee system designed to hold back floodwaters in the Mississippi river ended
up collapsing in many areas due to poor construction and a lack of proper
maintenance
Hurricane Safety in Coastal Areas
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Listen to a radio or television for weather updates and stay in touch with your
neighbors about evacuation orders.
Plan a place to meet your family in case you are separated during a disaster.
Choose a friend or relative out of state for your family members to call to report
how you are doing and get information about other family members in the area.
Assemble your disaster supplies kit. Make sure that you kit has plenty of food that
doesn’t require refrigeration or heating and that you have plenty of fresh water to
drink.
Storm shutters are the best protection for windows. If your house does not have
them, help an adult board up windows with 5/8" marine plywood. Tape does NOT
prevent windows from breaking!
Bring in outside furniture. If it can be done safely an adult should remove any
antennas or satellite dishes that may be attached to the house in any way.
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Help an adult shut off your utilities including water, electricity, and gas.
Make sure there is gas in the car and you are ready to evacuate immediately if
you are told to do so.
If you don’t need to evacuate, be sure to STAY INDOORS during a hurricane. The
strong winds that are associated with a hurricane can cause things to be torn out
of the ground and becoming dangerous objects that can hit you. Don’t be fooled if
there is a pause in the wind because this could just be the eye of the storm.
If you do evacuate, do NOT go back home until local officials say it is safe.
Federal Emergency Management Agency (FEMA)
The Federal Emergency Management Agency became part of the Department of
Homeland Security on March 1, 2003 and it is charged with helping people before and
after a disaster strikes. Disasters include things such as hurricanes, tornadoes, floods,
earthquakes, and any other event that causes wide spread damage and loss of life.
FEMA is called in to help a particular area when the governor of a state that has been
affected by a disaster calls the President and asks for help from the federal government.
FEMA workers help disaster victims find a place to stay if their homes are
damaged or destroyed and can also aid in helping the city reconstruct public buildings
that are vital to the health and safety of the community. FEMA also helps people before
a disaster strikes so they can be better prepared for what might happen. In this role
they teach people how to make their homes as safe as possible and stock up on
supplies they may need if there is no electricity or fresh water available. FEMA also
works with communities to help them build safer, stronger buildings that are less likely to
be damaged in the event of a disaster, train firefighters and emergency workers, and
runs a flood insurance program.
The Department of Homeland Security, which includes FEMA, is the newest
cabinet-level department in the federal government. It was proposed by President
George W. Bush after the terrorist attacks of Sept. 11, 2001 and was then approved by
Congress. This new department combined 22 different agencies or federal programs into
one and made protecting the nation against further terrorist attacks the number one
priority.