Hurricanes and Storm Surges
And Air Circulation (Winds)
Air pressure and winds
 Air is a fluid
 Warmer air is less dense
 Air moves from dense to less dense conditions
 Ex.: Land-sea breezes
Global air circulation
 Equator receives most insulation
 Hot air rises, heads towards poles
 Air becomes heavy and sinks at 30°N and S
 Plus the Coriolis effect
Coriolis effect - is a deflection of moving objects when they are viewed in a rotating frame of Reference.
Main Points
 Warmer air “holds” more water
 Low pressure=warm air=precipitation
 High pressure=cold air=dry air
What is a hurricane?
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A large rotating storm with strong winds blowing at speeds of 74 miles per hour or more, around a
relatively calm center called the eye.
It blows counter clock-wise in the Northern Hemisphere, and clockwise in the Southern Hemisphere.
The whole storm system may be 5-6 miles high, 300-600 miles wide, and move forward like as
immense spinning top
Travels at speeds of about 12 mph
What causes a hurricane?
 Correct amount of warmth & water vapor to supply energy
 Convection activity & vertical wind motion to bring in air from sea level and move it up through the system
 Must be given the right amount of spin or twist, provided by the rotating earth
What is the eye of the hurricane?
 Innermost portion of the storm
 Light breezes or almost windless calm
 Clear skies, while winds and clouds continue raging around it
 On average, eyes are 14-20 miles across
Within the eye:
 Lowest pressure
 Highest temperatures
 Lowest relative humidity
 Eye not always in the center.
Why do hurricanes form over warm oceans?
 They draw their power from warm, extremely humid air found only over warm oceans.
 The key to their energy source is the latent heat that is released when water vapor condenses into cloud
droplets and rain.
 Grow best in a deep layer of humid air that supplies plenty of moisture.
 Grow where air converges and begins to push upwards.
 If the air is unstable, it will continue rising after the initial shove.
 When winds at all levels are blowing at the same speed in the same direction, the disturbance will grow.
 Grow above high pressure areas high above the ocean, which help pump away the rising air, allowing more air to
flow into the storm and rise.
What is storm surge?
 Piling up of water as it is pushed along by the storm
 When the storm nears land, the ocean bottom blocks the water from flowing away, and the dome of water
builds up to come ashore as the storm surge
 This dome of water can be as high as 18 feet deep as a storm hits land.
What is the difference between a hurricane and a typhoon?
 Nothing except geography.
 Tropical storms occur in several of the world's oceans, and except for their names, they are essentially the same
type of storm.
 In the Atlantic Ocean, Gulf of Mexico, and the Eastern Pacific Ocean, they are called hurricanes.
 In the Western Pacific Ocean, they are called typhoons.
 In the Indian Ocean, the Bay of Bengal, and Australia, these types of storms are called cyclones.