Tropical Storms

Brief notes and a few diagrams on Tropical Storms.

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Tropical Storms:
Distribution of Storms:
Storms include tropical cyclones, midlatitude storms and tornadoes.
Tropical cyclones (hurricanes in the Atlantic) are violent storms between 200km and
700km in diameter.
They occur in the latitude 520 north and south of the equator.
Once generated, cyclones tend to move westward.
Tropical cyclones or hurricanes will only occur over warm ocean (over 27C) of at
least 70m depth and at least 5N or 5S of the equator so that the Coriolis effect
(which is very weak at the equator) can bring about the rotation of air.
Effects:
Storms can cause damage in several ways, including heavy rain (leading to floods and
mudslides), high wind velocity and very low central pressure (leading to storm surges
and coastal flooding).
They can be devastating in lowlying megadelta regions (e.g. Hurricane Katrina in
New Orleans in 2005 and Cyclone Nargis in Myanmar in 2008)
Definition:
A tropical storm is a weather system of low pressure formed over tropical seas. It has strong
winds (sustained at over 74 miles per hour) and heavy rainfall. It can be called a hurricane,
cyclone, typhoon or wildwilly depending on the ocean it occurs in.
Features:
Huge circular body of thick cloud around 450km wide
Eye in the centre around 45km wide, usually no clouds in the eye. Formed because
cold air is descending in only that part
At the edge of the storm : Pressure and temperature higher; less cloud, wind and
rain.
At the vortex : Dense cloud; violent wind in gusts; thunderstorm and torrential rain.
At the eye : Very low pressure; clearer skies; temperatures warmer; torrential rain.

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Tropical storm from above
Crosssectional diagram of a Tropical Storm
Causes:
Temperatures above 27C are needed for sufficient evaporation to create a humidity
above 75%. Water also needs to be >60m deep, as storms stir up the water, bringing
cold water from below.…read more

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The storms form in low pressure areas where
trade winds converge.
The trade winds converge near the surface causing the warm and unstable air to rise.
The humid (moist) air supplies latent heat energy to the storm and the preexisting
winds feed the hurricane throughout its growth at all heights.
At highaltitudes the air diverges as it reaches the troposphere into a thick canopy of
cirrus clouds up to 1500km across.
As the storms move further away from their energy source, they fade.…read more

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Heavy rain ­ the tropical cyclone can pick up 2 billion tonnes of moisture per day and
release it as rain. This also leads to extensive flooding ­ often well inland.
Tornadoes ­ tropical cyclones sometimes create many tornadoes as they hit land.
Physical and human factors that determine the impacts:
Physical: wind speed, torrential rain and storm surges.
Human: development stages and preparation.…read more

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