geography

• are intense low-pressure weather systems that develop in the tropics.
• they begin in an area of low pressure, caused by surface heating, into which warm air is drawn in a spiralling manner.
• small-scale disturbances enlarge into tropical depressions with rotating wind systems.
• these may continue to grow into a much more intense and rapidly rotating system.

• an oceanic location with sea temperatures above 27 degrees - provides contiuous source of heat to maintain rising air currents.
• ocean depth of at least 70m - moisture provides latent heat, rising air causes moisture to be released by condensation - this drives the system,
• location at least 5 degrees north or south of the equator in order that the coriolis force can bring about the maximum rotation of air.
• low-level convergence of air in the lower atmospheric circulation system - winds have to come together near the centre of the low pressure zone.
• rapid outflow of air in the upper atmospheric circulation - this pushes away the warm air, which has risen close to the centre of the storm.

• occur between latitudes of 5 and 20 degrees north and south of the equator - once generated they tend to move westwards and are at their most desructive:
• caribbean sea/gulf of mexico area where they are kown as hurricanes.
• western side of central america
• Bay of Bengal wher they are known as cyclones
• off southeast asia where they are known as typhoons
• off madagascar
• in northwestern australia, where they are known as willy willies.

measured on the Saffir-simpson scale - 5 levels

scale 5 has:

• central pressure at 920mb or below
• wind speed 69ms or greater
• storm surge at 5.5m or greater

average lifespan for a storm is 7-14 days.