GCSE Geography | How Do Tropical Storms Form? (Weather Hazards 4)

A tropical storm is a spinning mass of cloud – between 80 to 100 occur each year, and in order to be able to compare them, we give them names. The first storm of the year usually starts with an A then B and so on, and they usually alternate between male and female names, eg. In 2017 we saw Harvey, followed by Irma, followed by Jose…all chosen in advance.. Names used for devastating storms are not re-used.

Tropical storms occur within the tropics between 5 and 30 degrees north and south – not actually along the equator. This is because the Coriolis effect is not strong enough there to make the storm spin. The Coriolis effect is the effect of the earth’s rotation.

The sea temperature needs to be at least 27 degrees – which is close to the temperature of a heated swimming pool, and why we don’t get tropical storms in the UK! The maximum sea temperature in the UK is 17 to 18 degrees. The sea temperature also needs to be at a depth of 60 to 70 metres. This provides the heat and moisture needed to cause the warm air to rise rapidly creating low pressure.

Let’s look at the formation and development a bit closer…

• The air is heated above the surface of warm tropical oceans – hence the need for at least 27 degrees.
• This warm air rises rapidly, drawing more air and large volumes of moisture from the ocean, causing strong winds.
• The rising air will cool and condense to form tall cumulonimbus clouds – this releases latent heat, which is energy that is released without a change in temperature, which powers the tropical storm. There will be low winds present that allow the tropical storm clouds to rise high without being torn apart.
• The winds start to spin upwards due to the Coriolis effect – the effect of the earths axis.
• In the centre of the storm there is the eye – where the conditions are calm - this is formed by cool air sinking, creating a zone of high pressure, leading to calm drier conditions.
• The storm will be steered by trade winds towards the land – once it makes landfall the energy will start to subside as the storm has lost its source of power – this is why most tropical storm damage occurs along the coast.