Tropical Cyclone
Credit: Credit: Image courtesy of Stony Brook University

Tropical cyclones are very dangerous and destructive weather systems. They leave a mass of dead bodies, rubble, flooding, uprooted trees and natural vegetation in tatters. They wreak havoc and leave a path of destruction behind. These systems develop in all warm tropical oceans. But, what gives rise to these destructive systems? What conditions are needed to allow their development? When we better understand these weather systems we are able to take the necessary precautions to save lives and protect our property.


Distribution of Tropical Cyclones

Tropical Cyclones are found in all warm tropical areas. They occur between 5° and 25° latitude in both hemispheres. They do not occur within 5° of the equator because Coriolis force is zero in this area. The cyclone require Coriolis force in order to form. In latitudes beyond 25° the temperatures are not high enough to allow them to operate.

Tropical cyclones occur in the Gulf of Mexico where they are known as Hurricanes. They are also found off the coast of China and Japan where they are called Typhoons. Around the north of Australia and on the east coast of Africa they are known simply as Tropical Cyclones.

THe systems form in the Tropical easterly wind belt. This causes the system to move from east to west. While moving from east to west, the system curves away from the equator. If it manages to reach higher latitudes it may curve back towards the east under the influenced of the westerly wind belt. Even though this explanation sounds very simple, the path of a tropical cyclone is very difficult to predict. These systems don’t follow a straight line and may change direction without warning.


Naming of Tropical Cyclones

Once formed these systems are named in order to identify and track them. At the beginning of the tropical cyclone season the first system to develop is given a name starting with an A. The next one gets a name with a B, etc. Cyclone Danny would therefore be the fourth system of the season.


Conditions needed for the Formation of Tropical Cyclones

Tropical cyclones form over the ocean where the sea surface temperature is above 26° Celsius (79°F). As the warm, moist tropical air rises it cools and condenses. During condensation more heat is released which causes the air to rise further. This condensation of moist tropical air is what fuels the system.

The rising air causes a low pressure to form. As the air rises, due to Coriolis force, it starts to rotate around the low pressure. The rising air pulls more moist air in from the sides which also rises and condenses. This continues to fuel the system further and the process speeds up. As more heat is generated the pressure drops further. The air starts spinning rapidly around the low pressure. The rising moist air causes the formation of massive cumulonimbus clouds. The consequence is that together with the strong wind you also have heavy showers of rain.


Formation of the 'Eye"

As the system takes shape an area of complete calm forms in the centre of the tropical cyclone. This is known as the ‘eye of the storm’. This is an area of about 25 km in diameter. The eye is an area of complete calm and experiences no wind or rain. It is roughly round and is surrounded on all sides by massive cumulonimbus clouds, rain, wind, lightning and raging storms.

The eye forms as a result of the small amount of air that is sucked down the centre of the system. The rapid spinning of the tropical cyclone causes some air to be pulled back down towards the surface. Sinking air brings stable conditions and creates the area of calm in the centre.