Download Unit 08B - El Camino College

Hurricanes Unit (Topic 8B) – page 1
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Hurricanes Unit
Hurricanes are huge and powerful tropical storms. They have wind speeds of 75 mph or more
and cover well over 100 miles. Fueled by warm ocean water evaporating during summer and fall,
hurricanes are enormously destructive, flooding the nearby land and drowning people. Different
parts of the world have different names for hurricanes. In East Asia they are called “typhoons.”
In the Indian Ocean, they are called “cyclones.” Our word “hurricane” comes from Hurican, a
Mesoamerican god of the wind.
1. How fast must the winds go for a tropical storm to be called a hurricane?
2. What creates the strong winds of hurricanes?
3. Where do hurricanes form, in the tropics, mid-latitudes, or near the poles?
Where do hurricanes form, in the low latitudes, the mid-latitudes, or the high latitudes?
(Hint: What is the latitude of the Equator? What is the latitude of the North Pole?)
4. List another name for a hurricane.
(In other words, what are hurricanes called in other parts of the world?)
5. During which season(s) – spring, summer, fall, and/or winter – do hurricanes typically
form?
Hurricanes Unit (Topic 8B) – page 2
How the ocean fuels hurricanes
Warm water fuels hurricanes by warming the air
above in two ways. The air is warmed by contact
with the surface of the ocean and evaporation of
warm ocean water. Of the two, evaporation is far
more important: it warms the air far more quickly.
LOTS of air rises,
LOTS of air comes
in from the side
= Strong Winds
The warmed air rises quickly, and lots of cooler air
rushes in from the sides to replace it. As the air
Winds
comes in from the sides, it too warms and rises as
part of the giant convection cells that make up
hurricanes. The warmer the air is, the faster the air
Ocean
rises, and the faster the air rises, the faster air from
the sides moves in to replace the rising air, resulting
in the strong winds of the hurricane. (The winds are the air that moves in from the sides to
replace the rising air.)
6. What is the main way in which ocean water warms the air of a hurricane?
7. What does the air do after it has been warmed by the ocean? Why?
The air warmed by the ocean (A)____________________ because
its density is much (B)________________________ than the rest of the air at the surface.
A: rises, sinks
B: higher, lower
8. Why does air come in from the sides of the storm?
The air comes in from the sides to replace the (C)___________________ air
which is (D)______________________ within the storm.
C: warm, cold
D: rising, sinking
9. What is air coming in from the sides of the storm? In other words, what part or aspect of the
hurricane does the air coming in from the sides represent?
Hurricanes Unit (Topic 8B) – page 3
10. Why are the winds of hurricanes so strong?
In other words, why does the air come in from the sides so fast?
Evaporating ocean water warms the air above it (A)_____________________,
so the air has a (B)_____________________ density.
Therefore, the air rises (A)_____________________, and
air comes in from the sides (A)_____________________ to replace the rising air.
A: quickly, slowly
B: very high, very low, not very high, not very low
As the warm, moist air rises upward, it experiences lower and lower atmospheric pressure,
because there is less air (atmosphere) above it, pressing down. The lower pressure cause the
rising air to cool and when it cools enough, the water vapor in the air condenses into clouds and
rain. Since lots of water evaporates from the ocean when the ocean’s surface is warm, the rising
air contains an enormous amount of water which eventually falls back down as rain.
11. How does the ocean create the rain that falls beneath a hurricane?
Ocean water (A) _________________________________________.
Then, the warm air and water vapor (B) _______________________________________,
which causes the water vapor to (C)____________________ and
(A)______________________________________________ into clouds and rain.
A lot of water vapor is available to become rain,
because the ocean water is very (C) ____________________,
so a lot of water (A) _______________________________________ from the ocean.
A: condenses, evaporates, condenses & then evaporates, evaporates & then condenses
B: rise, sink
C: warm, cool
Hurricanes Unit (Topic 8B) – page 4
Structure of a Hurricane
The center of a hurricane is primarily a place where air rises (except for the small “eye” at the
very center). Air outside the hurricane tries to move towards the center to replace the rising air,
but it turns away from the center because of the Coriolis effect; it cannot go directly in. Air keeps
trying to move towards the center and bending away, resulting in a slow, inward spiral. As the
air spirals in, it may warm, rise, cool, and sink several times. Thus, a hurricane is made up of
bands of clouds where the air is rising and gaps between them where air is sinking.
At first
Hurricane structure - National Oceanic and Atmospheric Administration.
Examine the bird’s-eye-view maps above on the right.
12. At first, what direction does the air move in? Why?
At first, the air (surface winds) try to move toward
the (A)____________________ spot
to replace the air which is (B)_______________________
there.
A: warm, cold
B: rising, sinking
13. Does the air turn to its right or left as it tries to go towards the center of the storm? Why?
14. As a result of the turn, does the air spiral clockwise or counterclockwise on its path
to the center of the storm?
Hurricanes Unit (Topic 8B) – page 5
Death and Destruction caused by Hurricanes
Hurricanes cause damage in a variety of ways. Obviously, the strong winds can fling objects
around and tear down buildings. In addition, hurricanes produce an enormous amount of rain.
However, the most devastating aspect of a hurricane by far is the hurricane’s storm surge. Sea
level rises beneath hurricanes, more than 3 feet in the open ocean. This may not seem like much,
but the strong winds of the hurricane push the mound of water against the land, causing more and
more water to pile up: sea level can go up 20 feet or more! So when hurricanes hit the coast, they
flood the shoreline. In addition, huge waves created by the strong winds can reach much farther
up the shoreline thanks to the storm surge. These waves cause much of the damage.
90% of hurricane victims drown, primarily due to storm surge. Hurricane flooding causes much
more property damage than their winds, which is why insurance companies will not insure
against flooding. You have to buy flood protection from the national flood insurance program
run by the federal government.
15. How do most people die when a hurricane strikes the coast?
● drown: flooding by rain
● drown: flooding by rising sea level
● lightning
● strong winds
(flying objects & collapsed buildings)
16. What aspect of hurricanes causes most of the property damage?
● flooding by rain
● flooding by rising sea level
● lightning strikes
● strong winds knock down buildings
Hurricanes Unit (Topic 8B) – page 6
Why does the ocean rise beneath a hurricane? The
ocean is pushed down strongly beneath the higher air
pressure outside the hurricane, so the ocean rises
beneath the hurricane where the downward push is
weaker. (The water is that is pushed down has to go
somewhere. This is somewhat like a “see saw” or
“teeter-totter”: if one end goes down, the other must
come up.) Hurricanes are associated with low
atmospheric pressure, because the air in a storm
system is warm, rising air. Warm air expands (get
“bigger”), so there is less air above each location (it
has spread off to the side), and therefore less weight
above (less pressure) as well.
Air
Molecules
Land
Ocean
17. Why is the atmospheric pressure lower beneath a hurricane?
(A)__________________ ocean water below the hurricane (B)__________________ the
air above it, which causes the air to (C)_________________________________________.
A: warm, cold
B: warms, cools
C: get heavier, get lighter, spread out, contract
18. Why does the surface of the ocean rise beneath lower atmospheric pressure?
Where atmospheric pressure is higher,
the air pushes down more (D)_________________ on the ocean, so water is pushed
from the place with (E)___________________________ atmospheric pressure
to the place with (E)___________________________ atmospheric pressure
D: strongly, weakly
E: higher, lower
19. Where is sea level highest along the coast, where the winds of the hurricane push water
towards the land or away from the land?
Hurricanes Unit (Topic 8B) – page 7
Why hurricanes typically hit some coasts, but not others
Hurricanes typically strike the east and southern coasts of the United States each summer and
fall. Both the winds and ocean currents that we have studied contribute to the danger along the
eastern and southern coasts of the United States.
Examine the map below showing the prevailing wind pattern.
A
B
20. What direction do the winds blow in the tropics?
21. What direction will the hurricanes move when pushed by these winds?
(Hint: Consider how the Coriolis effect will influence their path.)
Sketch the path hurricanes forming at dot A and B will follow.
22. Do these winds push hurricanes that form in the tropics towards the east coast and away
from the west coast, or towards the west coast and away from the east coast?
Hurricanes Unit (Topic 8B) – page 8
Examine the map below showing the boundary currents along the coasts of the United States.
23. Does the current along the east coast of the United States move north or south?
Does this mean it is a warm current or a cold current?
Will the current along the east coast of the United States strengthen hurricanes as they
approach the coast and help them travel along the coast or weaken them?
24. Does the current along the west coast of the United States move north or south?
Does this mean it is a warm current or a cold current?
Will the current along the west coast of the United States strengthen hurricanes as they
approach the coast and help them travel along the coast or weaken them?