Why do some tropical storms intensify and why do they dissipate?

It is important to know what factors affect the distribution of tropical storms. The image below shows that most tropical storms form around 5° north and south of the equator. This is where the Coriolis effect starts, giving tropical storms their iconic spin. Other trigger factors that affect the formation of tropical cyclones include:

• high levels of humidity – moisture is a key building block of cyclones
• rapid cooling of air – to create high amounts of energy, the rising air needs to condense rapidly
• low wind shear – cyclones cannot form if the wind is blowing from different directions up through the atmosphere
• established low-pressure disturbances – when smaller storms converge, this allows the formation of tropical cyclones.

The ITCZ influence on cyclones

Due to the convergence of these trigger factors located in the ITCZ (the Inter-Tropical Convergence Zone), creating warm and moist air with strong prevailing winds, the ITCZ is the ideal source area for tropical cyclones to form.

Factors affecting tropical cyclone intensity

600 trillion watts of energy are produced from the heat energy generated by the condensation of warm, moist air. Only 3% of this energy is used in forming the cyclone’s strong winds or movement forward; the rest of the energy pushes air into the upper atmosphere. The warmer the water that fuels the cyclone, the more powerful and intense it will be.

Dissipation of tropical cyclones

The reduction in energy and intensity leads to the dissipation of tropical cyclones. There are three key reasons that cyclones dissipate:

1. When a cyclone reaches land, the warm water that fuels the cyclone is lost. However, if the cyclone tracks back over the sea, it can re-intensify. It is important to note that if a cyclone passes over a mountainous area, it can dissipate quickly, but this can lead to heavy rainfall, resulting in flooding and landslides.
2. Colder water (below 26.5°C) will lead to cyclone dissipation.
3. The change of wind direction, or wind blowing in different directions from other weather systems, can disrupt the cyclone. This change in wind direction can pull the cyclone apart.