Download Gorman Hurricanes PA5 Study Guide 1 Hurricanes • What is a

Gorman
Hurricanes
PA5 Study Guide
Hurricanes
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What is a hurricane?
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A tropical cyclone with sustained winds of 74 mph or higher.
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Large, atmospheric storm with spiraling bands of thunderstorms.
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A low pressure system with a defined wind circulation that develops over the tropics.
How does a hurricane form?
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Begins over warm tropical waters of 80 degrees F or hotter.
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Maritime tropical air masses form over these warm waters.
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Have all the right ingredients for thunderstorm formation.
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Lifting mechanism is caused by the heat of the tropical waters and winds entering
the low pressure area from opposite directions
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Has four distinct stages of development
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Lots of water vapor containing latent heat
Tropical disturbance
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Cluster of clouds, showers, and thunderstorms
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Remains intact for 24 hours or more
Tropical depression
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Winds circulating around a center of low pressure
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Winds at 38 mph or less
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Circulation is counterclockwise in the Northern Hemisphere
Tropical storm
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Given a name
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Winds 39 – 73 mph
Hurricane
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Winds of 74 mph or higher
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Strengthens from a tropical disturbance over days or weeks
Hurricanes “die” or weaken when they…
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Move away from warm waters
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Move over land
Where do hurricanes form?
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Gulf of Mexico
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The Caribbean Sea
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The Eastern North Pacific Ocean
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The North Atlantic Ocean
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Gorman
Hurricanes
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PA5 Study Guide
Many of the original thunderstorms develop over the western part of Africa and then
move out over the ocean.
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Tropical depressions, tropical storms, hurricanes, typhoons, cyclones, Willy-Willies are all
“tropical cyclones.”
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Hurricanes are categorized based on their wind speed.
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Saffir-Simpson Scale
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Scale of 1 to 5
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Cat 5 is the strongest
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Current version of the Saffir-Simpson Scale is based solely on wind speeds.
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Contains predictions of damage caused by certain wind speeds.
Watches and Warnings
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Tropical storm
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Watch – storm in your area POSSIBLE within next 48 hours
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Warning – storm in your area EXPECTED within next 36 hours
Hurricane
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Watch – hurricane conditions POSSIBLE in your area within next 48 hours
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Warning – hurricane conditions EXPECTED in your area within next 36 hours
Damage and Effects of Hurricanes
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Rainfall induced flooding
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Can occur from hurricanes
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Can occur from tropical depressions and storms that never reach hurricane
strength
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Can occur from downgraded hurricanes after they hit land
Storm Surge
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Most dangerous effect of hurricane.
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Caused by hurricane winds pushing water onto the shore.
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Greatest height of storm surge occurs on the right side of where the hurricane
makes landfall, because of counterclockwise rotation of winds.
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High Winds
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Cause much structural damage to buildings and property.
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Hurricanes
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PA5 Study Guide
Often stay strong enough to cause damage after the hurricane has hit land and has
been downgraded to a tropical storm or depression.
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Cause excessive damage when ground is saturated or flooding.
Tornadoes
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Created from supercell thunderstorms
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Often happens as hurricane is making landfall
Official Atlantic Hurricane Season
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Begins June 1 and ends November 30.
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Water takes a while to heat up.
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Warm waters begin to cool around end November.
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Most active mid September through October.
There are many other, seemingly unrelated factors which contribute to hurricane formation. You
do not need to know these now. We will discuss them later.
High pressure forms
and then most of the
air moves away. But,
some of the air trickles
back down into the eye
and clears it of clouds.
This usually happens
when the tropical
cyclone has reached
hurricane strength.
More specifics on hurricane formation.
Low Pressure forms.
The lower the pressure,
the faster the wind
moves in from the
surface high pressure
areas to this low,
updraft area.
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Hurricanes
PA5 Study Guide
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Strong thunderstorms occur.
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Air pressure drops at the surface of these storms.
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Low pressure attracts warm moist air from the ocean’s surface (air moves from high pressure to
low pressure as wind).
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The fuel for the tropical cyclone is the moisture from the warm ocean water.
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This moisture (water vapor) contains great amounts of latent heat.
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The moisture (water vapor) gives away this latent heat when the water vapor condenses to liquid
water to become clouds.
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More air moves into the low pressure area, rises rapidly, and condenses into more clouds and
rain.
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This added condensation releases even more energy into the atmosphere.
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As the updraft gets stronger, a lower pressure area forms and the winds move faster from the
surrounding areas to the low pressure area.
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As long as warm, moist air is available, the tropical cyclone continues to refuel itself.
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Power is concentrated in a donut shaped area called the eye wall.
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The eye wall surrounds the eye (center) of the tropical cyclone.
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The eye wall typically contains the strongest surface winds.
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Sinking air trickling down the center of the tropical cyclone clears it of clouds and forms the
"eye."
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But air moving away from the very top of the eye ensures a relatively low pressure area even
though some air is sinking.
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Typically, an "eye" forms when the tropical cyclone reaches hurricane strength, but an eye is not
necessary for a tropical cyclone to become a hurricane.
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The Coriolis Force causes the winds to spiral in a counterclockwise direction around the center of
the low in the Northern Hemisphere. (Winds swirl clockwise in the Southern Hemisphere.)
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Tropical Cyclones do not occur within 300 miles (500 kilometers) of the equator because there is
no Coriolis Effect at the equator.
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The Coriolis Force (Effect) is caused by Earth’s rotation. You do not need to know any more
about the Coriolis Effect for PA5.
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