The Characteristics of Tropical Cyclones
- Tropical cyclones are rotating, intense low-pressure systems (below 950mb)
- Characteristics include:
- Lasting 7-14 days
- Heavy rainfall
- High wind speeds (over 119 kmh)
- High waves and storm surges
- Tropical cyclones can vary in diameter (100-1000km)
- Winds spiral rapidly around a calm central area known as the eye, with descending cold air, low pressure, light winds, no clouds or rain
- The winds of the storm are not constant across its diameter
- The outer edges of the storm have lighter wind speeds, smaller and more scattered clouds, rain is less intense, and the temperatures begin to increase
- The strongest and most destructive winds are found within the eyewall, with spiralling storm clouds, torrential rainfall and low temperatures
- Tropical cyclones are rated on the five-point Saffir-Simpson scale based on wind speeds
- Tropical cyclones are considered major when they reach category 3 and have wind speeds between 111-129 miles (178-208 kilometres) per hour
- A category 5 storm can deliver wind speeds of more than 157 miles (252km) an hour
Anatomy of a tropical cyclone
Exam Tip
Make sure you know how storms develop, along with a few of the main characteristics and how climate change may affect them.
Being able to draw and annotate the formation of a tropical storm will gain you credit, or you may be asked to complete a diagram in the exam.
Stages of tropical cyclone formation
- In the right conditions, a tropical cyclone can form rapidly and follow a number of stages:
- Warm, moist air rapidly rises, forming an area of low pressure
- Air from high-pressure areas rushes in to take the place of the rising air
- This air then rises, forming a continuous flow of rising air
- As the air rises, it cools and condenses. This releases heat energy, which helps power the tropical cyclone
- Air at the top of the storm goes outwards away from the centre of the storm
- The Coriolis force causes the rising air to spiral around the centre.
- Some of the air sinks in the middle of the storm, forming a cloudless, calm eye
- The tropical cyclone moves westward from its source
- If a tropical cyclone makes landfall or moves over an area of cold water, it no longer has a supply of warm, moist air and loses speed and temperature; therefore, rainfall and winds decrease
Exam Tip
Remember, conditions such as warm oceans and the Coriolis Force exist at all times, but tropical cyclones do not form all the time.
It is the combination of all the right conditions coming together that leads to tropical cyclone formation.