What is Tropical Depression

A tropical cyclone is a disturbed state of the atmosphere, most often characterized by a low pressure center and several thunderstorms, which eventually produce strong winds and heavy rains. Based on their intensity, the tropical cyclones are broadly categorized into three groups - tropical depressions, tropical storms and cyclones (also known as typhoons and hurricanes depending on their location.)

Tropical Depression

A stage of a tropical cyclone, it is an organized system of clouds and thunderstorms with a surface circulation of less than 39 mph. Though the depression doesn't have an 'eye' or the spiral shape, which characterizes powerful storms, it is indeed a low pressure area and hence is referred to as a depression. The wind speed is measured at a height of 10 m above the water surface and averaged over a minute for data calculation. This depression mostly forms in the tropical regions of the planet, in maritime tropical air masses and hence it is referred to as tropical depression. While tropical storms are named alphabetically, these depressions are numbered.

How does a Depression Form?

Cyclones are most often formed in the tropical areas, 5° and 20°North and South of the Equator, owing to the Coriolis effect. Initially, a low pressure zone is formed in this area, which eventually forms a tropical wave of low pressure. This disturbance in the warm ocean waters, along with a light wind at the upper level, provides ideal weather condition for the formation of storms. With time, the intensity of the tropical wave may either increase or decrease. If the intensity increases, it goes on to become an organized area, characterized by heavy showers and thunderstorms. This organized area, marked by cyclonic winds blowing clockwise in northern hemisphere and anti-clockwise in southern hemisphere, is referred to as tropical depression. Equatorial areas, 5°North and South of the Equator, do not facilitate the formation of storms due to the lack of rotary motion of wind in this area.

Tropical Storm

A tropical storm is a stage of tropical cyclone characterized by an organized system of strong thunderstorms with surface circulation between 39 mph and 73 mph. Although the 'eye' is not present, the spiral cyclonic shape starts to develop in this stage. When the system reaches to this intensity, it is given an alphabetical name by the authorities.

The storm system which starts as a depression eventually takes the form of a severe cyclone which can create havoc on the planet. Hurricane Katrina, one of the most devastating cyclones experienced in recent times, is the best example of how dangerous cyclones can become. Owing to the rapid climate change the planet has been experiencing over last few decades, tropical depressions and cyclones have only become more frequent. In a bid to gain supremacy over nature, the human race has created a conducive environment for these natural disasters and more importantly, we are yet to realize our mistakes.