How do tropical storms form?

The Formation of a Tropical Storm

Tropical Storms start between 5º and 30º north and south of the equator, where surface sea temperatures reach at least 26.5ºC, which is about the temperature of a heated swimming pool. This is why we don’t get tropical storms in the UK.

Air is heated above the surface of these warm tropical oceans. The warm air rises rapidly under low-pressure conditions.

The rising air draws up more air and large volumes of moisture from the ocean, causing strong winds.

The Coriolis effect (spinning movement of the Earth) causes the air to spin upwards around a calm central eye of the storm.

As the air rises, it cools and condenses to form large, towering cumulonimbus clouds, which generate torrential rainfall. Heat is given off when the air cools and powers the tropical storm.

Cool air sinks into the eye. Therefore, there is no cloud, so it is drier, clearer and much calmer.

The tropical storm travels across the ocean with the prevailing wind.

When a tropical storm meets land, it is no longer fueled by the moisture and heat from the ocean, so it loses power and weakens.

The diagram below summarises the formation of a tropical storm.

Warm Ocean Temperatures
Tropical storms form over oceans where the surface temperature is at least 26.5°C.
Low Pressure System
Rising warm, moist air creates a low-pressure area that draws in more air and moisture.
Cloud Formation
As the moist air rises, it cools and condenses to form cumulonimbus clouds and heavy rain.
Coriolis Effect
The rotation of the Earth causes the rising air to spin, forming the storm’s circular motion.
Storm Growth and Movement
The storm is powered by heat from condensation and is steered by prevailing winds across the ocean.
Weakening Over Land
Once the storm reaches land or cooler water, it loses its heat source and begins to weaken.