Transcript Tornadoes

Tornadoes
….a violently rotating column of air extending from a
thunderstorm to the ground.
Although tornadoes occur in many
parts of the world, they are found
most frequently in the United
States.....
• rotating winds of more than 250 mph.
• can be one mile wide and stay on the ground
over 50 miles.
• may appear nearly transparent until dust and
debris are picked up or a cloud forms within
the funnel.
• waterspouts are tornadoes which form over
warm water. They can move onshore and
cause damage to coastal areas.
How Tornados Form
• Form when cold dry polar air
meets warm moist tropical air, this
is common in the Tornado Alley
• Tornadoes start deep within vast
thunderclouds
• a column of strongly rising warm
air is set spinning by high winds
streaming through the cloud's top.
• As air is sucked into this swirling
column, it spins very fast,
stretching thousands of feet up
and down through the cloud, with
a corkscrewing funnel descending
from the cloud's base - the
tornado.
Tornado Formation
Click on picture to access interactive tornado
Tornado Alley
• Severe T-storms form when cold dry polar air
meets warm moist tropical air, this is common
in Tornado Alley
Tornado Alley
How Tornados are Classified
• Enhanced Fujita Scale
• It classifies tornadoes into six different
categories
• EF0 through EF5 - based on the degree of
damage created by the tornado
Hurricanes
also known as tropical cyclones and typhoons
• It can take anywhere from hours to days for a tropical
disturbance to develop into a hurricane. But if the cycle
of cyclonic activity continues and wind speeds increase,
the tropical disturbance advances through three stages:
4step formation
•
•
•
•
Thunderstorm
Tropical depression: wind speeds of less than 38 mph
Tropical storm: wind speeds of 39 to 73 mph
Hurricane: wind speeds greater than 74 mph
Hurricanes
Northern Hemisphere/Southern Hemisphere
Counterclockwise rotation
Northern Hemisphere
Clockwise rotation
Southern Hemisphere
How do Hurricanes Form?
• Hurricanes only form over
really warm ocean water of
80°F or warmer.
• the atmosphere (the air)
must cool off very quickly
the higher you go.
• the wind must be blowing
in the same direction and
at the same speed to force
air upward from the ocean
surface.
• Winds flow outward above
the storm allowing the air
below to rise.
• Hurricanes typically form
between 5 to 15 degrees
latitude north and south of
the equator.
• The Coriolis Force is
needed to create the spin
in the hurricane.
Select diagram to go to interactive
Hurricane formation
How it Works
Hurricane Facts
• official hurricane season for the Atlantic Basin is from 1 June to 30
November. The peak of the season is from mid-August to late October,
however, deadly hurricanes can occur anytime in the hurricane season.
• The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the
hurricane's present intensity. This is used to give an estimate of the
potential property damage and flooding expected along the coast from
a hurricane landfall. Wind speed is the determining factor in the scale.
• Typical hurricanes are about 300 miles wide although they can vary
considerably in size.
• The eye at a hurricane's center is a relatively calm, clear area
approximately 20-40 miles across.
• The eyewall surrounding the eye is composed of dense clouds that
contain the highest winds in the storm.
Hurricane Facts
• The storm's outer rainbands (often with hurricane or
tropical storm-force winds) are made up of dense bands of
thunderstorms ranging from a few miles to tens of miles
wide and 50 to 300 miles long.
• Hurricane-force winds can extend outward to about 25
miles in a small hurricane and to more than 150 miles for a
large one.
• Tropical storm-force winds can stretch out as far as 300
miles from the center of a large hurricane.
• Frequently, the right side of a hurricane is the most
dangerous in terms of storm surge, winds, and tornadoes.
Storm Surge
• As a hurricane’s winds spiral
around and around the storm,
they push water into a mound
at the storm’s center.
• The water piles up, unable to
escape anywhere but on land as
the storm carries it landward.
•
A hurricane will cause more
storm surge in areas where the
ocean floor slopes gradually.
• When high tide happens at the
same time as a storm surge, the
combination of the two is called
storm tide. During a storm tide,
the water level may be 20 feet
or more above normal.
Select icon to access
Interactive storm surge
HURRICANES AND TORNADOES
What's the difference?
• both form in warm, damp air when winds blow into
each other from opposite directions.
– Hurricanes develop over warm, tropical oceans
– the winds swirl around in a spiral at up to 200 mph
– In the middle is a calm "eye" 4 - 25 miles wide, surrounded
by the worst wind and driving rain.
– tornadoes form over land and are more violent
– A tornado is a tall, funnel-shaped whirlwind of cloud up to
2,000 feet high.
– In the middle is an eye of descending air, surrounded by a
strong upward current that sucks up or destroys everything
in its path.
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