What is a hurricane?

  • Hurricane is the most devastating and violent type of tropical cyclone.
  • Tropical cyclones are circular storm that originate over warm tropical oceans and is characterized by low atmospheric pressure, high winds and heavy rain. There is no frontal formation. (A front is a boundary separating two air masses of different densities.)


Where do they originate?

  • They are formed in the Atlantic, Carribean Sea, Gulf of Mexico, Central and Northeastern Pacific.


How do they develop?

  • The ocean in the tropical regions is at least 27 degree Celsius for upto at least 50m below the surface.
  • Due to this, the air just above the ocean surface becomes warm.
  • The warm and moist air over the tropical regions acts as fuel for tropical cyclones.
  • Water vapours formed over the ocean form cumulonimbus clouds. After this, the development of tropical cyclone passes through 4 stages:
  1. Tropical disturbance: The rising temperature produces strong upward rising winds, which carry water droplets upwards, where they freeze and fall down again. The swift movement of water droplets along with the rising air creates lightening and sound. This is called THUNDERSTORM (at 40-60kmph).
  2. Tropical depression: When the wind speed crosses 60kmph, it turns into a tropical depression. Water takes up heat from atmosphere to change into vapour. When the vapours change into raindrops, heat is released back to the atmosphere, which warms the air around. The warm air rises, creating a low pressure area at the centre.
  3. Tropical storm: At such high speed, it becomes a storm.
  4. Cyclone: As the storm reaches the speed of 120kmph, it becomes a cyclone. Cyclone has a low pressure system with very high speed winds revolving around it. At this stage, the storm is 50, 000 ft high, 200 km across and has an eye 8-48 km wide. (Eye: It is the central calm area of the cyclone. It is free of clouds and has light winds.)



Features of hurricane/cyclone

  • These are systems of intense low pressure.
  • They have the lowest pressure at the center& strong winds blow into the center from high pressure area.
  • These winds are deflected into an anti-clockwise direction in the northern hemisphere and clockwise direction in the southern hemisphere.
  • They rush upwards with a great force creating a vortex which is the area that surrounds the eye of the cyclone.
  • The rapidly rising air gives rise to torrential rains and the strong winds cause damage.
  • They occur in the tropical latitudes 5° and 20° South and North of the equator, in autumn when sea temperatures are at their highest.
  • They form over warm oceans where sea temperatures exceed 26°C.