Tropical Cyclone

A tropical cyclone is not just a strong storm — it is a precisely defined weather system that draws its energy from warm ocean water and releases it through violent winds, torrential rain, and storm surges. Before we get into its features, it helps to see where it sits in the larger scheme of natural hazards. The book groups natural disasters into four broad categories: atmospheric, terrestrial, aquatic, and biological. Tropical cyclones belong to the atmospheric group, alongside drought, hailstorms, frost, heat waves (or loo), and cold waves. The terrestrial group covers earthquakes, volcanic eruptions, landslides, avalanches, subsidence, and soil erosion. The aquatic group deals with ocean- and water-related hazards, and the biological group with living organisms as agents of disaster.

Now, to the cyclone itself. A tropical cyclone is a rapidly rotating storm system that originates over warm tropical oceans. Its defining characteristics are a low-pressure centre, very strong winds that spiral inward, and heavy rainfall. The entire system is driven by the latent heat released when moist air rises, cools, and condenses into clouds and rain. This is why tropical cyclones only form where sea-surface temperatures are high enough — typically above 26–27°C — and why they weaken quickly once they move over land or cooler water, because their fuel supply is cut off.

The structure of a mature tropical cyclone is distinctive. At the centre lies the eye, a region of calm, clear skies and relatively low winds. Surrounding the eye is the eyewall, a ring of the most intense thunderstorms and the strongest winds in the entire system. Beyond the eyewall, spiralling rainbands extend outward, bringing bands of heavy showers and gusty winds. The whole system can span hundreds of kilometres, though the most destructive weather is concentrated near the centre.

Tropical cyclones are classified by their wind speed, and the book follows the standard intensity scale. A system with sustained winds below 39 km/h is called a tropical depression. When winds reach 39–61 km/h, it becomes a tropical storm. At 62–88 km/h, it is a severe tropical storm. Once winds exceed 88 km/h, the system is officially a tropical cyclone — and at the very top of the scale, with winds above 118 km/h, it is a very severe tropical cyclone. These thresholds matter because they determine the level of preparedness and the damage a storm can inflict. …