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A hurricane is a tropical cyclone that forms over oceans. A tropical cyclone is a type of storm characterized by a low-pressure center and thunderstorms with strong winds and rain. Depending on location and strength, a tropical cyclone can be known as a hurricane, typhoon, tropical storm, cyclonic storm, or tropical depression. A hurricane’s wind speeds must be at least 74 mph. If the wind speed ranges from 40 to 73 mph, it is known as a tropical storm and assigned a name. Tropical cyclones with maximum surface winds less than 39 mph are known as tropical depressions.
Hurricanes are the most common, as they occur in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E. Next are typhoons, which occur in the Northwest Pacific Ocean west of the dateline (on the right of the map). A severe tropical cyclone occurs in the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E. Severe cyclonic storms occur in the North Indian Ocean, while tropical cyclones occur in the Southwest Indian Ocean.
A hurricane is made up of three important parts. These parts are the eye, the eye wall, and the rain bands.
The eye, the calmest part of the hurricane, is located at the hurricane’s center and can have a width of 20-40 miles. There is usually very little wind and rain near it. It has the lowest atmospheric pressure in the hurricane. The eye will develop when the maximum sustained wind speeds exceed 78 mph. As the storm strengthens, the eye decreases in size. In strong tropical cyclones, the eye is characterized by light winds and clear skies. In weaker tropical cyclones, it’s less defined and can be covered by the central dense overcast, an area of high, thick clouds.
The eye wall surrounds all or most of the eye. It consists of a ring of thunderstorms that produce heavy rains and strong winds. The side of the eye wall where the wind blows in the same direction as the hurricane’s forward motion is the most destructive part of the hurricane. Changes in the eye wall can cause changes in wind speed, which is an indicator of the hurricane’s intensity. When the eye either grows or shrinks in size in category three hurricanes or stronger, concentric or double eye walls can form. This is called the eye wall replacement cycle.
Rainbands are curved bands of clouds that trail away from the eye wall. They spiral slowly counterclockwise and range in width from a few miles to tens of miles. They are capable of producing heavy bursts of rain and wind. The outer rain bands can extend a few hundred miles from the eye of the hurricane. Their length ranges from fifty to three hundred miles. Rain bands are part of the evaporation/condensation cycle that feeds the hurricane. Tornadoes often form in the rainbands that are located on land.
Answers: 2 1 3
In order for a hurricane to form, a thunderstorm must undergo a continual evaporation-condensation cycle of warm, humid air. Surface winds must occur at higher altitudes. There must be a difference in air pressure between the surface and high altitude.
Hurricanes form in the warm tropical waters over 80 degrees Fahrenheit or 27 degrees Celsius. As warm air rises rapidly from the surface of the ocean, its water vapor forms storm clouds and rain droplets, releasing latent heat of condensation. The heat warms the cool air and causes it to rise; the air is replaced by warm ocean air. The cycle repeats, causing continuous circulation of air from the surface to the atmosphere. This causes an exchange of heat that creates a pattern of wind.
Winds at the ocean surface converge and push warm air upward, speeding the rising of air and the storm. Strong winds continue to blow and maintain the storm’s speed. The storm loses organization and weakens when there’s a difference in wind speeds. High-pressure air in the atmosphere removes heat from the rising air, further driving the hurricane’s growth. Wind speeds increase as high-pressure air is sucked into the low-pressure center of the storm. Hurricanes can last for more than two weeks over open water, but loses power on land or over cool waters, and its winds gradually die down.
The movement of a hurricane is controlled by large-scale winds, the streams in the Earth’s atmosphere. Hurricanes rotate in different directions depending on their location.
Tropical systems are steered westward by east to west winds, also known as trade winds. The earth’s rotation contributes to the acceleration that causes cyclonic systems to turn towards the poles in the absence of strong currents. This is known as the Coriolis Acceleration or Effect. When a storm’s center crosses the coastline, it is called landfall. The landfall area experiences only half the storm.
The hurricane’s path of motion is referred to as a tropical cyclone’s track. Its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north.
Dissipation occurs when a hurricane moves over land, which deprives the storm of warm waters that power it, disorganizing it into low pressure areas. A hurricane remaining in one area too long uses all the warm surface water. It then draws up cooler water that cannot support the hurricane. Moving over water with temperatures below 26 degrees Celsius also causes a loss of strength. The formation of an outer eye wall ends the convection in the inner eye wall, causing the storm to lose power and stop. Artificial dissipation has been attempted, but tropical cyclones are too large.
Answer: The Coriolis Effect
Hurricanes are given names and categorized by the Saffir-Simpson scale, created in 1969 and used mostly in the Western Hemisphere.
The Saffir-Simpson Hurricane Scale is a scale with a 1 to 5 rating on a hurricane’s intensity. Many factors such as potential property damage, amount of flooding expected along the coast, and particularly wind speed, determine the hurricane categories.
To be considered a category one hurricane, the storm must have wind speeds of 74-95 mph with a storm surge generally 4-5 feet above normal sea level. Not much damage is done to homes and other buildings, unless they are unanchored, such as mobile homes. There is only minor coastal road flooding and damage. Hurricane Lili of 2002 and Hurricane Gaston of 2004 were category one hurricanes.
Category two hurricanes have wind speeds of 96-110 mph with a storm surge generally 6-8 feet above normal. Some minor parts are damaged in homes and buildings, such as window and roofing material. More damage occurs in shrubbery and plants, and whole trees can completely get blown down. There are chances of 2-4 hour floods along the coast. Hurricane Frances of 2004 and Hurricane Isabel of 2003 were both category two hurricanes.
Category three hurricanes must meet the wind speed of 111-130 mph with a storm surge of 9-12 feet above normal. Structural parts of buildings may be damaged. Floods can reach many miles inland, and street signs are completely demolished. It may even require the evacuation of low-lying residences along the coast. Category three hurricanes include Jeanne and Alex of 2004.
To be a category four hurricane, a storm must have a wind speed of 131-155 mph with a storm surge generally 13-18 feet above normal. Extensive damage to building structures and roofs can be caused by category four hurricanes. All sorts of shrubbery and large trees are completely destroyed. Major damage can be done to low floors of coastal floors. Hurricanes Charley and Dennis were category four hurricanes.
Category five hurricanes must have wind speeds greater than 155 mph with a storm surge of greater than 18 feet above normal. Complete homes can be washed away by the floods and winds. Low-lying residences within 10-15 miles of the shoreline must be massively evacuated. Hurricanes Katrina and Wilma of 2005 were considered deadly and put in category five.
The Saffir-Simpson scale is based upon the Richter scale for hurricanes. Although the Saffir-Simpson scale categorizes hurricanes based upon wind speed and potential damage, it does not consider location and precipitation. This means that a lower category hurricane may actually do more damage than a higher categorized one.
Tropical cyclones are named according to where they occur. Each section has a list of male and female names which are reused every six years. Hurricane names alternate between female and male, so if the first hurricane has a male name, it will be followed with a female name and vice versa. All the letters of the alphabet except Q, U, X, Y, and, Z are used when creating names. If all the names on a list have been used, storms are named after the letters of the Greek alphabet.
Answer: Wind speed
Hurricanes are capable of destroying buildings, large trees, and people. Between Category one and Category five hurricanes, the difference between the costs to repair this damage is between thousands of dollars to billions of dollars. To prevent further damage, scientists use a variety of tools to observe and predict hurricanes.
A dissipating storm releases much rain, causing fatal mudslides and floods. Depending on the category of the hurricane, there can be a range of minimal damage to extensive damage. Buildings can be damaged and sometimes washed away by floods and winds. People can be killed or severely hurt by category four and five hurricanes. Often, evacuation is required to prevent deaths in an area.
The cost of repairing damage done by a hurricane depends on its intensity, the location it hits, and response. Category one hurricanes cause little damage; therefore, there’s minimal cost for repair. Category two and three hurricanes cause a significant amount of damage. Trees are often uprooted, and structural damage to residences occurs. Evacuation near the coast is needed. This can range between thousands and hundred thousands of dollars. Category four and five hurricanes cause extensive damage. Homes can be wiped away, and people can be killed. To repair the damages done by Hurricane Katrina, 100 billion dollars were spent.
To prepare for a hurricane, you should know about your community’s emergency plans, warning signals, evacuation routes, and locations of emergency shelters. You should also identify potential home hazards and know how to secure or protect them before the hurricane strikes. Electrical power, gas, and water supplies should be turned off before you evacuate. Structurally unstable building materials should be secured. After a hurricane strikes, it is important to discard any food that may have been touched by water. Don’t start any fuel-burning devices; there may be a chance that carbon monoxide could poison or kill you.
When far from land, hurricanes are tracked by satellites with visible and infrared imagery that produce quarter- or half-hour updates. When near land, Doppler radar that has minute-by-minute is used. Doppler radars update on the storm's location and intensity. Small government aircrafts are sometimes flown into hurricanes.
A hurricane's track is predicted by the position and strength of high- and low-pressure areas. High-speed simulation software produces forecast models of the track. The intensity of the storm is the least accurately predicted. Computer models are also used to predict rainfall.
Although hurricanes mostly cause destruction, they are also known to have several beneficial effects. Hurricanes bring precipitation to hot and dry areas and moderate the global heat balance by moving warm air to cooler regions. The storm stirs up the waters of coastal fish breeding areas. It also spurs redevelopment of housing, which increases property value.
Global temperatures have been increasing, which causes an increase in precipitation, thus in turn, causing an increase in hurricane intensity. Hurricanes thus have increased wind speeds and heavier precipitation because of the increase in water temperatures, which fuels hurricane growth. The annual number of storms has stayed about the same, but hurricane intensities have greatly increased.
Answer: Satellite Doppler radar Airplanes
The Great Hurricane of 1780 is known as the deadliest hurricane ever recorded, killing over 22,000 people! It was a category 4 hurricane, sustaining a wind speed of 150 mph. This hurricane first struck Barbados, and then continued on to other neighboring islands such as Martinique, Puerto Rico, and the Dominican Republic, and thousands perished in each place.
Hurricane Ivan of 2004 reached a sustained wind speed of 165 mph, meeting the required speed for category 5. It originated in the Atlantic Ocean, and then moved over the Windward Islands over the Caribbean Sea. Its damage totaled to more than $19 billion.
Hurricane Katrina of 2005 was the costliest and deadliest hurricane in the history of the United States. It was the sixth-strongest hurricane ever recorded in the world. Katrina was a category 5 hurricane and had maximum sustained wind speeds of over 175 mph. It started as a category 1 hurricane over the Bahamas and gradually made its way to category 5 over Louisiana and Mississippi. Over $81 billion was lost in destruction.
Hurricane Paul of 1982 was the second deadliest East Pacific storm, with over 1,000 deaths. It was a category 2 hurricane with more than $70 million in damage and a maximum sustained speed of 110 mph. Paul first hit land in Central America, and it later moved north to the Baja California Peninsula. It caused major flooding and severe mudslides.
Technical Producer: Sarah
regional name for a tropical
low-pressure center and
< 39 mph winds
> 40 mph winds
Typhoon Axel and Cyclones Mark and Betsy
Names of Tropical cyclones
with winds greater than 74 mph
• Calm center 20-40
• Winds and rain stop
• Sea may be violent
• Lowest atmospheric
pressures in the
The Eye Wall
• Surrounds the eye
• Greatest wind speeds
• Eye wall
eye may change size,
causing another eye
wall to form.
outer eye wall
inner eye wall
• Ring of thunderstorms that
• Width: few miles to tens of
• Length: 50-300 miles
• Calm weather between
• Tornadoes often form in
rainbands on land.
Match the following items to their characteristic quality:
1. Most destructive
2. Lowest pressure
3. Causes tornadoes
Controlled by winds
Earth’s rotation causes
hurricanes to turn
eye crosses coastline,
which experiences only
half the storm.
The Coriolis Effect
path of motion.
Track is deflected
north by winds.
Global cyclone tracks
How a Hurricane Loses Strength and Disintegrates
Moving over land or low
Remaining in one area
for too long.
Outer eye wall forms.
What is the effect that causes hurricanes
The Coriolis Effect
to turn towards the Earth’s poles?
“At last!! They’ve named a hurricane
after you and your mother!”
The Saffir-Simpson Scale
intensity on scale of 1-5.
Wind speed: 74-95
(Slightly higher than top speed of
Storm surge: 4-5 feet
Little damage and
Wind speeds: 96-110
(Top speed of baseball pitch)
Storm surge: 6-8 feet
Slight damage on
buildings and plants.
Chances of floods
Wind speed: 111-130
(Speed of bullet train)
Storm surge: 9-12 feet
Damage on building
evacuation may be
Wind speed: 131-155
(Wind speed of leaf blowers)
Storm surge: 13-18
Major damage to
buildings, trees, and
Wind speed: > 155
(Diving speed of Peregrine falcon)
Storm surge: > 18 feet
Homes can be washed
must be evacuated.
…Because Fremont’s really going to get hit by a hurricane.
Be aware of emergency plans and procedures.
Identify potential hazards.
Shut off utilities (gas, electricity, water).
Discard contaminated food.
Don’t start fuel-burning devices.
Far from land: tracked by
Near land: tracked by aircrafts or
Doppler updates on location and
Track predicted by
produces models and
Intensity of storm
Moderates global heat
Stirs up waters of coastal fish
Spurs redevelopment of
Name one of the tools used to track
Why can’t true
There’s no water!
hurricanes form on
Great Hurricane of 1780
• Deadliest hurricane ever recorded
• Category 4
• Struck the Caribbean Islands
Hurricane Ivan (2004)
• Category 5
• Moved from
to Caribbean Sea
• Cost: $19 billion
Hurricane Katrina (2005)
• Costliest and deadliest
• Category 5
• Moved from Bahamas to southern U.S.
• Cost: $81 billion
Hurricane Paul (1982)
• Second deadliest East Pacific storm
• Category 2
• Moved from Central America to Baja
• Caused flooding and mudslides
What are the two planets (besides Earth)
Saturn and Jupiter
that have cyclonic storms?
CDC Emergency Preparedness & Response
The Pew Center
Atlantic Oceanographic and Meteorological La
Cyclone Tracy Meteorological Information
University of South Florida
The NASA SCIence Files
Mission 2010 [MIT]
The National Center for Atmospheric Research
Vantage Point Guides
Weather Wiz Kids
State of New Hampshire Natural Hazards Mitigation Plan
NOAA Satellite and Information Service
Associated Press: Hurricane Season 2006
National Climatic Data Center Merry-Go-Round
of Life [Howl’s Moving Castle]
ASesgui @ Youtube.com