Transcript Hurricanes What is a hurricane?

Weather and Severe Storms
The Sun provides the energy that drives
Earth’s weather by unevenly heating the land
and water, and by heating the equator and
poles by different amounts.
http://www.youtube.com/watch?v=6hD52H7rQak The Sun as the driving force behind
for wind and water currents and earth’s temperatures
Air masses, of different temperature and
humidity, move from areas of high pressure to
areas of low pressure, creating wind.
Why would the area indicated in the map
below be considered unseasonably warm?
•Look at the
jet stream.
•Since the jet
steam is so far
north, the
warm tropical
air from the
South would
come further
north
Climate is the long term pattern of
temperature and precipitation in an area
Weather is the short term variations in
temperature, humidity, air pressure, and
wind.
http://www.climatecentral.org/videos/web_features/climate_vs_weather
Weather happens every day, but only some
days have storms
Storms vary depending on their temperature,
if they are coming off the ocean or continent,
and the season.
The severity of the storm depends on
whether or not they strike a populated area.
Examples of severe storms
•Thunder and lightning storms
•Tornadoes
•Hurricanes
•Blizzards
• For the test you need to be able to:
• distinguish one storm from another
and
• identify why they only form in certain areas of
world during certain times of the year
Thunderstorms
•What is it?
A storm with thunder and lightning and typically
also heavy rain or hail.
•What causes a thunderstorm?
• Moisture, unstable air, and lift.
• You need moisture to form clouds and rain. You need
unstable air that is relatively warm and can rise rapidly.
Finally, you need lift. This can form from fronts, sea
breezes or mountains.
When are thunderstorms most likely to occur?
Thunderstorms can occur year-round and at all hours.
But they are most likely to happen in the spring and
summer months and during the afternoon and evening
hours. Why?
•Warm, moist air rises, forming cumulus, then
cumulonimbus clouds.
•The water vapor condenses, it collects together and
forms rain drops or hail.
•As rain or hail falls, a downdraft is created, which
cuts off rising warm air and stops the storm.
Thunderstorm Formation
Lightning
•Uneven electrical charges occur in a cloud as rain
drops and hail move in a convection current in the
cloud.
•The lightning occurs in an attempt to equalize the
uneven charges.
Tornadoes
Tornadoes
•What is a tornado?
A tornado is a violent rotating column of air
extending from a thunderstorm to the
ground.
Other Names for Tornadoes
• Tornado comes from the Spanish word,
tronada, which means “thunderstorm.”
Other names for tornadoes are twisters,
dust devils, whirlwinds, waterspouts, and
cyclones.
R- Dust Devil, Center- Water Spouts, L- Fire Devil
•In severe
thunderstorms, winds
are moving in different
directions and at
different speeds at
different heights.
•This difference in wind
direction and wind
speed is called wind
shear.
Wave Clouds (or Tsunami Clouds, or KelvinHelmholtz Clouds) seen in
Van Gogh’s “Starry Night” painting
•A strong updraft tilts the wind shear and
produces rotation inside the tornado. A funnel
cloud appears.
Tornado Alley
 Tornadoes in the U.S. are most likely to
occur in a region known as Tornado
Alley.
Did Dorothy from the Wizard of Oz live in
“Tornado Alley?”
Any place thunderstorms occur, a tornado can
happen.
In the United Kingdom, Polar continental air mixes
with Tropical Maritime air producing tornadoes
Tornado Categories
• The Fujita-Pearson
Tornado Intensity Scale or
F-scale ranks tornadoes by
their wind speed.
• F0- winds 40-72 mph
• F1- winds 73-112 mph
• F2- winds 113-157 mph
• F3 – winds 158-206 mph
• F4 – winds 207-260 mph
• F5 – winds > 261 mph
Tornado
Precautions
• Go to a basement, if you have one.
• Get in the innermost room of your house.
Avoid rooms with windows. Bathrooms are
good.
• Crouch with arms above your head.
• If outside, lie in a ditch or get under a
bridge.
• If you live in an area with a frequency of
tornadoes, listen to forecasts.
Hurricanes
Hurricanes
• What is a hurricane?
Hurricanes are a system of strong winds spiraling inward
and upward at speeds of 75 to 200 mph counterclockwise
around a low pressure center
• Swirling air rises and cools, forming clouds and
precipitation
• Hurricanes form over warm (82 degree +) water and have
winds 74+ mph
Formation of a Hurricane
• Hurricanes are storms that form over tropical
waters. The hurricanes that affect the eastern
coast of the United States form off the western
coast of Africa where the water is warm, the
air is humid, and the winds converge.
Tropical Disturbance
•Hurricanes start out as a group of storms that
begin to rotate when they meet converging winds.
These storms create violent seas that send more
moisture into the air. The water vapor rises and
helps the wind increase in speed. If the storm
holds itself together for 24 hours, we call it a
tropical disturbance.
Tropical Depression
• Tropical cyclones are
areas of low pressure
that develop over
tropical waters. We
call them tropical
depressions if their
wind speeds are more
than 25 mph and less
than 38 mph.
• A tropical
disturbance becomes
a tropical depression
if it lasts more than 24
hours.
Tropical Storm
• A tropical
depression
becomes a tropical
storm when its
winds rise above
38mph.
• It is called a tropical
storm if the winds
are between 39 and
73 mph.
Hurricanes
• A tropical storm becomes a hurricane
when its winds exceed 73 mph.
Hurricane Categories
• Category 1 – Winds between 74- 95 mph
• Category 2 – Winds between 96- 110 mph
• Category 3 – Winds between 111-130 mph
• Category 4 – Winds between 131-155 mph
• Category 5 – Winds above 156 mph
Hurricane Facts
• Hurricanes can be very big, even as big as the
state of Ohio! They can be seen from outer
space.
• The entire formation and life of a hurricane takes
days or weeks.
• Because hurricanes seldom travel in straight
paths, meteorologists predict several paths.
• Hurricanes usually lose power as they travel over
land.
• Hurricanes destroy beaches, buildings, and
vegetation.
• Hurricanes bring strong winds, heavy rain, storm
surges, flooding, and tornadoes.
Hurricane Protection
• Watch weather forecasts.
• Board up all windows and doors
• Have bottled water, food, batteries,
medicine, and important documents
• Call someone and let them know where
you are
• Photograph valuables for insurance
• Take care of your pets
Hurricane Isabel
Hurricane Andrew
 The path of Hurricane Andrew over three consecutive days
can be seen below.
Super Storm Sandy
Blizzards
 A blizzard is a long-lasting snowstorm with very strong
winds (35+ mph) and intense snowfall.
When and where do blizzards occur?
 They are common in winter when the jet stream travels
south and a cold northern air mass comes in contact with a
warmer, semi-tropical air mass.
 When the cold, continental polar air mass
travels over a lake, it can pick up more
moisture and produce “Lake Effect” snow
blizzards
Lake Effect Snow
Blizzards & Ice Storms
Review
1.
2.
3.
4.
5.
6.
Which is larger, a hurricane or a tornado?
Which moves faster, a hurricane or a tornado?
Which lasts longer?
Where do hurricanes form?
Where do tornadoes form?
What do we call the area of the US that has a
high occurrence of tornadoes?
7. How long do tornadoes last?
8. How long do hurricanes last?
9. Name two precautions in the event of a
tornado.
10. Name two precautions in the event of a
hurricane.
Severe Weather

Type of Storm
Where Forms
Typical Time
of Year
Thunderstorms
Within large
cumulonimbus
clouds
Spring or
Summer
Seek shelter,
avoid trees
and water.
Cumulonimbus
cloud
Spring, early
summer
Move to a storm
shelter or basement
if possible; stay
away from windows
and doors.
Over warm
ocean water
Late summer
and into
autumn
Tornado
Hurricane
Safety Rules
Evacuate or
move inside a
well-built
building.
WEATHER SERVICE MAPS
ISOTHERMS are lines joining
places on the map that have the
same TEMPERATURE
–Do you see the connection between
“isotherm” and “thermometer”
WEATHER SERVICE MAPS
ISOBARS are lines joining places
on the map that have the same AIR
PRESSURE
–Iso means “equal”
–Bar means “pressure”
Why doyou think it’s called a barometer?