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Severe Weather:
Tornadoes and Hurricanes
Grab Toto!!
TORNADOES
Are a low pressure storm that usually
forms over land
in an average year, 800 tornadoes are
reported in the U.S.
a tornado is defined as a violently
rotating column of air extending from a
thunderstorm to the ground… the
rotating column of air is called the vortex
the vortex is only visible when debris
and dirt gets carried up with the winds
THE HOOK
Where do they come from?
Tornadoes come from the
energy released in a
thunderstorm.
What makes them
dangerous (as compared to
hurricanes) is that their
energy is concentrated in a
small area, only a hundred
yards across
When & Where do they
occur?
Most common east of the
Rocky Mountains and west
of the Appalachian
Mountains.
They occur mostly during the
spring and summer (AprilJune)
They usually occur during the
late afternoon and early
evening.
Usually happen along cold
fronts
How long is a tornado usually on
the ground?
Can range from a few seconds
to several hours ...
5 minutes is average
How fast do tornadoes move?
Movement can range from
virtually stationary to more
than 60 miles per hour ...
Average is 10-20 miles per hour.
Watch—means conditions are
favorable for tornado to
develop
Warning—means that tornado
has been spotted
THE WIND!
• Take a look at
this piece of
wood that
was driven
into the palm
tree.
LOOK
AT
THESE
MEASURING DESTRUCTION
The Enhanced Fujita Scale rates tornadoes based on
the amount and type of wind damage produced.
EF-0. Light damage
Wind 65 to 85 mph. Causes some
damage to siding and shingles
EF-1. Moderate damage
Wind 86 to 110 mph. Considerable roof
damage. Winds can uproot trees and
overturn single-wide mobile homes.
Flagpoles bend.
EF-2. Considerable damage
Wind 111 to 135 mph. Most single-wide
mobile homes destroyed. Permanent
homes can shift off foundation. Flagpoles
collapse. Softwood trees debarked.
EF-3. Severe damage
Wind 136 to 165 mph. Hardwood trees
debarked. All but small portions of houses
destroyed.
EF-4. Devastating damage
Wind 166 to 200 mph. Complete
destruction of well-built residences and
large sections of school buildings
EF-5. Incredible damage.
Wind +200 mph. Significant structural deformation of
mid- and high rise buildings.
Strong frame houses leveled off foundations and swept
away; automobile-sized missiles fly through the air in
excess of 100 yards
May 25th, 2008
Catastrophic damage was reported in
Parkersburg as much of the town was
destroyed, with reports of flattened
houses and debarked trees. Six
people were killed in Parkersburg and
at least two fatalities were reported
where a housing development was
destroyed. At least 70 people were
injured
At 9:45 p.m. on May 4, 2007, Greensburg was hit by an EF5 tornado. The tornado
was estimated to be 1.7 miles (2.7 km) in width and traveled for nearly 22 miles
(35 km). Ninety-five percent of the city was confirmed to be destroyed, with the
other five percent being severely damaged. The National Weather Service
estimated winds of the tornado to reach 205 mph (330 km/h). This was the first
tornado to ever be rated EF5 since the update of the Fujita scale.
HURRICANES
Low pressure systems that form over warm, tropical
waters near the equator
Most form between 5 and 20 degrees north latitude
— they almost never form in the South Atlantic
Different names are given to hurricanes depending on
where they form
1. Atlantic—we call them hurricanes
2. Pacific—they are called typhoons
3. Indian Ocean—they are called cyclones
•Mature hurricanes average about 350 miles across
•They have the lowest barometric pressures ever
recorded with any storm (905 millibars is lowest recorded)
•These huge air pressure differences is what creates the
rapid, inward spiraling of winds
HURRICANE DEVELOPMENT
When winds have
developed
speeds from 39
to 73 miles per
hour, it is called a
tropical storm
(storms are given
names when
they begin to
have winds of
this speed).
2005 Katrina Developing
The storm becomes
a hurricane when it
reaches a wind
speed of over 74
mph
Hurricane
Formation
When a
season is
very
active,
Greek
letters are
used to
name
tropical
storms
after the
letters of
the
alphabet
had been
used.
THE END OF A HURRICANE
When a hurricane travels over land or cold water, its
energy source (warm water) is gone and the storm
weakens, quickly dying.
HURRICANE SEASON
•Occurs from June through November
•Most hurricanes form during the late summer
months because the ocean is still retaining heat
from the warmer earlier months
MEASURING DESTRUCTION
We use the Saffir-Simpson scale to rank hurricane
intensities
Saffir-Simpson Scale
CATEGORY
WIND SPEED
DAMAGE
74-95 mph
STORM
SURGE
4-5 feet
1
2
3
4
5
96-110 mph
111-130 mph
131-155 mph
Greater
than 155
6-8 feet
9-12 feet
13-18
Greater
than 18
Moderate
Extensive
Extreme
Catastrophic
Video Clip on Wind Tunnel
Minimal
STORM SURGE ACCOUNTS FOR 90%
OF
HURRICANE-CAUSED DEATHS
Category 5 Status includes:
Hurricane Wilma (October 2005) -- Gulf of Mexico, Yucatan
Peninsula, Mexico, Cuba, and Southern Florida
Hurricane Rita (September 2005) -- hit Texas, Louisiana
Hurricane Katrina (August 2005) -- hit southern Louisiana, Mississippi
and Alabama
Hurricane Isabel (September 2003) -- hit North Carolina, Maryland,
Delaware, Virginia, and Washington, D.C.
Hurricane Andrew (August 1992)-- hit southeastern Florida and
southeastern Louisiana
Hurricane Camille (August 1969) -- hit Mississippi, SE Louisiana, and
Virginia
AMAZING EARTH SCIENCE FACTS
High pressure systems move clockwise and outward
_______
Low pressure systems (ex. hurricanes) move
_______
counterclockwise and inward.