Download Hurricanes

8B – Slide 1
Topic 8B:
Hurricanes
Online Lecture:
Hurricanes
○ What Causes Hurricanes?
○ Structure of a Hurricane
○ Death and Destruction
Hurricanes Names
from Around the World
○ Hurricanes go by many names:
– name comes from Huracan
(meso-american God of wind)
– also called:
● Typhoon
(East Asia)
● Cyclone
(Indian Ocean)
● “Willy-Willy”
(Australia)
8B – Slide 2
Hurricanes are
tropical storms
which have become
very strong
(75+ mph winds).
8B – Slide 3
Strong Winds & Rain of Hurricanes
are Fueled by Very Warm Ocean Water
○ lots of evaporation
of ocean water warms
the air above the ocean
Air rises quickly owing
to its low density.
LOTS of
air rises,
LOTS of
water
condenses
= LOTS
of Rain
Winds
Rising air contains
a lot of water vapor.
Ocean
Hurricane “season” is from June to the end of November.
Why can hurricanes form as late as
November?
Draw
on the Board
Isn’t the water too cold?
8B – Slide 4
Spiral Shape of a Hurricane
Warm,
Rising
Air
Warm,
Rising
Air
Air tries to move towards the center,
but it bends away because of the
Coriolis effect: it cannot go in
directly in, but must spiral in slowly
Hurricane Structure
8B – Slide 5
As the air spirals in, it is
(1) warmed & picks up
moisture from the ocean
surface, (2) rises, (3)
cools & loses its water
as rain, (4) sinks back
down, and begins the
process (steps #1-4)
again – it goes through
it several times
Eye
“Eye Wall”
where the
winds are
strongest
8B – Slide 6
Coasts in Danger
Why do most hurricanes
strike the east &
southern coasts of the
United States?
Equator
Hint:
Think about
winds and/or
currents.
Equator
Death & Destruction Caused by Hurricanes
8B – Slide 7
○ Damage property and kill people in a variety of ways:
– strong winds
– lots of rain (flooding)
– “storm surge”:
What causes
the most deaths
and damage?
FEMA &
Flood Ins.
● sea level rises (20+ feet) beneath the hurricane,
so the shoreline is flooded by ocean water, like a
very high high tide, carrying huge waves inland
8B – Slide 8
What Causes Storm Surge?
○ Hurricanes are zones of low atmospheric pressure,
because warm air spreads out (“expands”), so there
is less air above each location pressing down.
○ The sea surface goes
down in places where
it is pushed down strongly,
but it must rise elsewhere
where the downward push
is weaker to compensate
(the water has to
go somewhere).
Low
Pressure
Land
High
Pressure
Storm Surge & the Winds of Hurricanes
8B – Slide 9
The strong winds of the hurricane pushes the “hill”
of water into shallow water and up against the land.
The water cannot go forward quickly enough and
the water cannot go down, so it rises upwards.