Hurricanes – How they are formed
Hurricanes are a global phenomenon. A hurricane is a powerful, spiralling storm that begins over a warm sea near the equator. Depending upon its location and strength, a hurricane is known by different names such as tropical cyclone, typhoon, tropical storm, cyclonic storm, tropical depression and simply cyclone. History is replete with powerful hurricanes that have struck civilization causing havoc such as hurricane katrina, hurricane gustav, hurricane isabel and hurricane wilma – just to name a few.
Birth of a Hurricane
At one time or the other all of us might have wondered how a hurricane is formed right? Here is how it happens.
A hurricane’s birth can be divided into 4 steps namely :
- Tropical disturbance – A cluster of thunderstorms form in an area with sea surface temperatures above 26 degrees Celsius, pushing warm humid air up into the atmosphere.
Tropical disturbance
- Tropical depression – The pressure falls as the thunderstorms grow bigger and start to merge. As air flows towards the low pressure zone, it picks up more energy from the warm sea surface and also starts to rotate due to Coriolis forces. Wind speeds up to 63 km/hr.
Tropical depression
- Tropical storm – The system takes on a circular shape as it becomes more organised, with a clear centre. Wind speeds up to 117 km/hr, with heavy rain.
Tropical storm
- Tropical hurricane – The storm turns into a highly organised hurricane as wind speeds exceed 117 km/hr. A relatively calm, cloud free zone called the eye appears at its centre, surrounded by spiral rain bands. It is from this feature of the hurricane that English language has borrowed the phrase – “Calm before the storm” – which means a quiet period just before a period of great activity or excitement.
Tropical hurricane
So remember – as long as a tropical storm has wind speeds below the magic number of 117 km/hr, it is called a storm. Only when the wind speeds exceed 117 km/hr is it called a hurricane.
[References : Wikipedia , NewScientist.com].
