MICROFlCliE RlTERENCE LIBRARY

MICROFlCliE RlTERENCE LIBRARY
MICROFlCliE
RlTERENCE
LIBRARY
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WHAT IS A HURKICALVE?
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WHAT ISAHLJRRICANE?
1.
What is a hurricane?
A hurricane
is a tropical
storm in which the winds reach speeds of over
74 miles per hour (120 Kph) and blow in a large spiral around a relatively
storms bring destruction
to
calm center or eye. Every year these violent
coastlines
and islands which lie in their erratic
paths.
Stated simply,
hurricanes
are giant whirlwinds
in which the air moves in a large, tightening
spiral around a center of extre"le low pressure,
reaching maximum velocity
in
a circular
band extending outward twenty or thirty
miles (30-50 km) from the
edge of the center (or the eye) of the hurricane.
Near the center, winds may
gust to more than 200 mph (320 kph), and the entire storm dominates the ocean
surface and lower atmosphere over tens of thousands of square miles (square
kilometers).
2.
How are hurricanes
formed?
In order for a hurricane
to form, it must have a WXTII sea and still
air.
In the Gulf of Mexico and the Caribbean, these condiLions normally occur in
the months of June through November. The warm air rises -- heavy, humid and
full of water vapor.
It's place is taken by air rushing in from the' sides and,
because of the earth's
rotation,
this moving air is given a twist so that the
entire system begins to revolve.
The warm rising
air meets cooler air and
releases its water vapor in the form of rain.
It takes a lot of energy for
the air to lift
the water in the first
place, and now th",s energy is released
in the form of heat.
This increases the rate of ascent of the air, and a continuous cycle begins to develop.
More water is released,
and thus more heat.
The more water and heat released,
the faster the cycle goes, and it soon
becomes much bigger.
Because the wind system is revolving,
centrifugal
force tends to throw
the air outwards so the pressure in the center becomes very low, thus forming
the eye of the hurricane.
The pressure on the outside is very high, so the
wind moves faster and faster in an attempt to fill
that low pressure area.
However, the faster it moves, the more the centrifugal
force throws it outwards.
Soon there are very fast, circular
winds; and once they reach 74 mph
(120 kph), the system becomes a hurricane.
Once this process is established,
the storm begins to move forward,
like a spinning top that moves along the
ground.
This brings it into contact with more warm sea and air, and the
prqcess
becomes self-sustaining.
Once a hurricane
has formed, it will continue
to move and expand until either it moves onto the land or it runs into an
area where the sea is cooler.
3.
What do hurricanes
look like?
From the top., hurricanes
appear like
they are very sharp and well-defined,
but
quite ragged.
In the Gulf of Mexico and
counter-clockwise.
The following
picture
very large spirals.
At the center
on the edges they tend to become
the Caribbean, hurricanes
rotate
shows how a typical
hurricane
in the
4
Gulf of Mexico or the Caribbean
above:
4.
In what direction
looks
do hurricanes
to a satellite
several
hundred miles
move?
Hurricanes
in the northern hemisphere generally
move in a northwesterly
direction;
however, they often shift direction
and become very erratic.
Very
little
is known about what makes hurricanes
move and change directions,
but it
is known that they are affected by the high altitude
winds and the rotation
of
the earth.
At present,
scientists
do not have the means of predicting
in advance.exactly
where a hurricane
will strike land.
Therefore,
they are always
dangerous, as they can change direction
without any warning.
5.
How fast
do hurricanes
move?
Hurricanes
usually begin moving forward at about lo-15 mph (15-25 kph), but
they pick up speed as they continue to move northward.
By the time they strike
land, they may be moving forward as fast as 60 mph (95 kph).
2
.7
6.
How fast
are the winds?
Wind speeds vary depending on the distance from the edge of the hurricane
to the eye. The winds at the outer edge may be merely large gusts ranging from
74 to 100 mph (120-160 kph).
Close to the eye, however, the winds may be
moving as fast as 200 mph (320 kph).
It is these winds near the center of the
storm which do the most damage.
-
-
7.
How large
are hurricanes?
large
Hurricanes may be as small as thirty
as 200 miles in diameter (320 km.).
8.
How far
inland
does a hurricane
miles
in diameter
(50 km.) or as
go?
Hurricanes begin to lose their strength as soon as they cross over land,
because they are denied the warm water that is necessary to keep them moving.
Usually the winds begin to slow down as soon as the eye of the storm has
However, the storm may continue to move inland with
crossed the shoreline.
destructive
force for as much as one hundred miles (160 km.) or more, depending
upon the original
size of the hurricane.
Yet the farther
inland they move,
the less force they will have. Most of the damage will occur in an area
usually no more than thirty
or forty miles (50-60 km.) from the coas&tline.
However, some hurricanes
suddenly turn around and go back out to sea where
they may rebuild
their strength and come ashore again at another place.
9.
What is the eye of a hurricane?
The eye of a hurricane
is its center.
In the eye, winds are light and
skies may appear to be clear or partly clouded.
The center is very calm
usually,
but this is very deceptive because, as soon as the eye has passed
over, the hurricane-force
winds will begin again.
Many persons have been
injured or killed
when the calm eye lured them out of shelter and they were
caught in the open in the high winds at the far side.
When the eye of a
hurricane
has passed, wind blows from the direction
opposite that from where
the winds blew before the eye passed.
The eye of a hurricane
is normally 10
to 30 miles in diameter (15-50 km.).
10.
What is the most dangerous
part
of a hurricane?
The winds of a hurricane
do the most damage to structures,
but most of the
deaths caused by these storms come from the rain and flooding which accompany
the hurricane.
As the storm approaches and moves across the coastline,
it brings
huge waves and raises the tides sometimes 15 feet (4.5 meters) or more above
normal.
This rise may come rapidly
and produce flash flooding
in the coastal.
lowlands;
or it may come in the form of giant waves which are mistakenly
called
"tidal
waves".
Waves and currents erode the beaches and the barrier
islands,
undermine buildings,
The torrenand wash away roads and irrigation
ditches.
tial rains which accompany hurricanes
can also produce flooding.
As the storm
moves inland and its winds diminish,
floods constitute
the greatest
threat.
Hurricanes may also cause tornadoes at the outer edge of the storm system.
These tornadoes may be the worst killers
and do most of the damage at the edge
of a hurricane.
A tornado is a small funnel of air which spins very rapidly and
moves along the ground destroying
things in its path.
Tornadoes also move in a
northwesterly
direction.
They are generally
small and only do damage in the
.
3
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areas where they actually
touch the ground.
several hundred yards (meters) in diameter.
What can be done to protect
11.
yourself
A tornado
is usually
no more than
and your house from hurricanes?
A.
Enter each season prepared.
Every June through November, check
all the major components of your house to make sure that they are
Especially
check the corners of the building
to
still
strong.
make sure that the wood is still
strong.
Check the base where
termites or moisture may have eaten or rotted the wood. Check to
make sure that the roof is securely tied to the walls, especially
at the corners.
If you are using bracing in the walls, check to
see that the braces are still
strong and .securely fastened to the
vertical
posts.
B.
When you first
hear that a hurricane
is approaching,
listen
to the radio for future messages.
C.
When your area receives a hurricane warning, plan your time before
the storm arrives so that you avoid last-minute
hurry which might
leave you marooned and unprepared.
If your house is in a low-lying
area that might be swept by high tides or storm waves, move to other
areas which you know will be high above any possible flooding.
D.
Board up any windows or doors to protect anyone inside from winddriven debris.
Be sure to close off transoms and to seal louvered
windows and doors.
E.
Tie down or move inside any objects which might be blown away or
Articles
such as tools,
furniture,
loose wood, etc.,
uprooted.
can all become dangerous missles when hurled through the air by
the hurricane
winds.
F.
Store drinking
water in clean containers
and cooking utensils,
because the water supply may be contaminated by flooding.
G.
If you have a radio or other battery-powered
make sure that you have an adequate supply
H.
Store fuel
kept dry.
I.
When a hurricane
comes, stay at home if it is a sturdy house on
high ground.
If it is not, move to another area of shelter on
high ground and stay there until
the storm is over.
If your house
is on high ground, remain indoors during the hurricane.
It is
extremely dangerous to be outside when high winds and tides are
seek shelter
whipping through the area.. If your house is on stilts,
in another building.
J.
If the
Beware of the eye of the hurricane.
directly
overhead, there will be a lull In
few minutes to half an hour or more. Stay
emergency repairs are absolutely
necessary.
side of the eye the winds rise very rapidly
and they come from the opposite direction.
for
cooking
and for boiling
.
4
water
be sure to
equipment,
of batteries.
in a place
check to
that
can be
calm storm center passes
the wind lasting
from a
in a safe place unless
Remember, at the other
to hurricane
force again,
K.
and help others
After the hurricane
has passed, stay in your village
unless you must seek emergency medical assistance
in another area.
Once the storm has passed, remember that hurricanes
moving inland
can produce severe flooding.
Stay away from riverbanks
and streams.
And if you are still
in a low-lying
area, move to high ground until
you are sure that the danger of flooding
has passed.
L.
Tornadoes spawned by hurricanes
are among the storm's worst killers.
When a hurricane
approaches,
tornadoes can be expected to develop.
If you see a tornado, seek shelter
inside immediately.
If a tornado
catches you outside,
move away from its path at a right angle.
If
there is no time for escape, lie flat in the nearest depression such
or against an embankment.
as a ditch,
FCC:jwp
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