Download Hurricanes! Fundamental Question: What causes a hurricane to form

Hurricanes!
Fundamental Question: What causes a hurricane to form?
Directions: In your own words, summarize each of the following steps of hurricane formation into the
first column. In the second column, illustrate the steps of hurricane formation in the same row of the
description.
1. Most hurricanes that affect North America begin as storm systems off the coast of Africa, near
the equator, where it is warm. Warm water from the sea surface evaporates quickly, rising into
the air.
2. When the warm air rises off the sea surface, cooler air swirls into its place. This cool air absorbs
more moisture which warms the air, causing it to rise.
3. A cycle of warm air rising and cool air swirling into take its place, get warmed and rise continues.
4. As warm air rises higher, it begins to cool, which condenses the moisture into clouds of water
droplets. These clouds spin as air cycles between warming and cooling.
5. The warm ocean waters along the equator add fuel to the storms as they move, growing larger
and stronger. As the storms spin faster, a low-pressure “eye” forms in the storm center.
6. The more warm ocean water available, the stronger the storm grows. When winds reach 35
miles per hour, it is considered a tropical storm. When winds reach 74 miles per hour or more,
the storm is called a hurricane.
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Summary
Most hurricanes that affect North America
usually start off as a storm system by the
coast of Africa. This is because warm water
rises into the air quickly.
Warm air rises off the sea surface. After that,
cooler air takes the warm air’s place. The cool
air then starts to absorb more moisture and
the air warms up, causing it to rise. Warm air
on top, cooler air on bottom.
The cycle continues, warm air stays on top.
And it repeats, cold air absorbs moisture and
goes up. The cycle keeps repeating.
Warm > Cold > Warm > Cold
After the warm air rises higher until no more,
it cools. The moisture condenses and clouds
form. Thus, the cycle repeats.
The reason storms grow over warm ocean
water, is because the warm water is like fuel
to the storm. As the storm spins faster, a
calm, low-pressure “eye” forms.
The more the storm stays over warm ocean
water, the more the storm grows. When the
wind speed reaches 35 mph, the storm is
classified as a tropical storm. When is hits 74
mph, it’s classified as a hurricane.
Illustration
Hurricanes, also known as strong tropical cyclones, are the result of low pressure forming over very
warm tropical or subtropical waters. They have an organized cluster of thunderstorms and strong
surface winds, blowing in a circular motion around the area of low pressure.
Procedure:
1. Review the Weather Conditions/Situations Cards.
2. Decide which situations or conditions are needed for the formation of a hurricane.
3. Circle the cards that are needed for the formation of a hurricane.
Area of low pressure
Area of low pressure
Extremely cold
temperatures over the
Iceland glaciers
Extremely warm
temperature over the
Saharan Desert
Trade winds
Easterlies
Westerlies
Coriolis Effect
Antarctic Current
Gulf Stream Current
Convection
Strong jet stream
Very warm ocean
water
Very cold ocean water
Systolic pressure
Sustained winds of at
least 33 mph or 74 mph
Thunderstorms
Snow
Calm skies with little to
no wind
Closed circulation of
clouds
4. In the space provided, explain why you chose each one.

Area of Low-pressure: Low pressure (such as that along fronts) build convection
(thunderstorms) over the center. As the convection builds, it creates updrafts in the
center which draw in more energy to keep building the convection. The updrafts lower
the pressure which, in turn, increases the winds.

Very warm ocean water: Typically, you must have ocean temperatures at a minimum of
80 degrees F as well as light winds in the upper atmosphere.

Thunderstorms: Waves (areas of sharp change of winds at the surface) and other areas
of low pressure (such as that along fronts) build convection (thunderstorms) over the
center.

Sustains winds of at least 33m/s or 73 mph.: If it's anything below 73 mph it's NOT a
hurricane.

Closed Circulation of clouds: The updrafts lower the pressure which, in turn, increases
the winds. If there is a closed circulation (winds rotating around a point), you have a
tropical system or cyclone.
5. SHORT ANSWER. What causes hurricanes to form and move towards the United States?
There are multiple causes the make hurricanes form and move towards the United States. Some
are the wind direction and ocean currents. Most hurricanes that hit the United States begin
either in the Caribbean or the Atlantic. Many of the worst start as seedlings coming off the coast
of Africa. Like all tropical cyclones, a hurricane needs the warm water of the tropics, which feeds
a storm with energy, in order to form. The atmosphere must be laden with moisture. So really
the "winds" control the movement of the hurricane.