This document contains useful information for the natural hazards topic for geography a level. It contains two case studies as well as other information about tropical storms
The largest hurricanes are located at the 30 degree latitude mark. They are located in
the oceans and don’t travel far inland. They occur more often in the tropics North of
the equator rather than the South. East Asia had 3 or more typhoons a year whereas
South Asia had less than 1 cyclone per year. East Asia has the longest tropical storm
season. The tropical storms originate over deep oceans.
1. Where are hurricanes, cyclones and typhoons found?
Hurricanes-North West pacific
Cyclones- South east pacific to Indian Ocean
Typhoons- North west pacific ocean
2. Describe the track of tropical storms.
They develop in the tropics, measure 200-700 km across, and give rise to roughly
circular inward-spiralling wind motion and sustained wind speeds of over 75mph. When
hurricanes move over land, they usually start to weaken quickly because they no longer
have their source of fuel: warm moist air above the sea.
3. When do they occur?
Northern hemisphere tropical storm season : June- November
Southern hemisphere tropical storm season : November - April
4. Where are tropical storms more frequently found?
Explain the factors that are needed for tropical storms to form.
· Oceans
An ocean depth of at least 70m; This moisture provides latent heat. As the moisture
condenses it releases latent heat that powers the storm.
· Sea temperatures
Sea temperatures of 27 degrees celsius or above provides a continuous source of heat
in order to maintain rising air currents
· Atmospheric instability
Convergence of air in the lower atmosphere
, · Coriolis force
This is when winds in the atmosphere are bent in different directions by the motion of
the earth’s rotation. In the north it is bent to the right and in the south it is bent to
the south. This encourages large tropical storms to form into hurricanes.
· Uniform winds
Uniform winds allow for wind speeds to build up
What are the main characteristics of a hurricane?
Hurricanes have three main parts, the calm eye in the centre, the eyewall where the
winds and rains are the strongest, and the rain bands which spin out from the centre
and give the storm its size. Strong winds, torrential rainfall and storm surges
accompany the hurricane.
Explain how hurricanes are formed?
Hurricanes begin life as thunderstorms over warm seas. More warm air rises and, due
to the earth’s rotation, starts to spin. The spinning accelerates as air rises faster and
draws in more warm air from the sea surface whilst sucking cooler air downwards. As
the storm moves over the ocean, it picks up more warm moist air. The speed of its
winds increase as more cold air is drawn into the eye. The eye is clear with calm winds
which are surrounded by a spinning vortex of high winds and heavy rain.
What is the role of latent heat in hurricane formation?
Latent heat is the name given to energy produced when a substance changes state i.e.
vapour to a liquid. As there is much condensation when clouds are formed in a tropical
storm, this releases heat which effectively powers the storm.
How are hurricanes measured and what is the limitation of the scale used?
Tropical storms are measured on the Saffir-Simpson scale, a five-point scale based
upon central pressure, wind speed, storm surge and damage potential.
It does not take into account:
● The amount and intensity
of rainfall.
● The relief of the land.
● The population density of
the area affected by the storm.
● What stage the storm is
when it hits land (mature or
decaying).
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