What are the causes of tropical storms?

BBC Bitesize – hurricanes

BBC Bitesize – hurricanes quiz

BBC Class Clips – formation of a hurricane

A tropical storm is a very powerful low-pressure weather system. It has strong winds and heavy rainfall that can be disruptive and dangerous.

For a tropical storm to form sea temperatures need to be 27c or higher. The sun’s energy causes water vapour to be evaporated creating lots of warm, moist air. This air rises through the atmosphere, creating low pressure at the surface and increases surface winds. The rising air cools and the water vapour in the air condenses to form clouds and eventually precipitation. The Earth’s rotation (Coriolis force) causes the storms to spin (anticlockwise in the northern hemisphere).

Tropical storms are enormous, measuring up to 644 kilometres wide and up to 8 km high. They move quickly in the atmosphere, at up to 60 km/h. The area in the middle of a tropical storm is the eye. The eye is up to 48 km across. It is an area of very light wind speeds and no rain, because the air here is descending. Huge cumulonimbus clouds surround the eye, creating the eye wall. When tropical storms reach a land surface, they begin to lose their energy and die out. This is because they are no longer receiving heat energy and moisture from the ocean, which is needed to drive them.

Image result for tropical storm diagram

Tropical storms bring two types of extreme weather:

  1. Extreme winds: these are caused by the area of very low pressure at the cenrte of the storm that creates a big pressure difference to the surrounding area. Tropical storms can have wind speeds of more than 250km/h. These winds are strong enough to damage or destroy buildings and plants, and cause loose objects to be picked up and transported. The winds, combined with low air pressure, also create storm surges.
  2. Extreme rain: high amounts of precipitation fall rapidly in tropical storms. This is because large amounts of warm, moist air are rising then cooling causing the water vapour to condense and form clouds. This rainfall can cause flooding and mudslides.