Tropical cyclone categories

Tropical cyclone severity and categories

The severity of a tropical cyclone is ranked in categories from 1 (weakest) to 5 (strongest).

The category given to a cyclone:

• is based on its maximum mean wind speed
• doesn't indicate the severity of other hazards the cyclone may bring. For example, a Category 1 cyclone can have significant impact through heavy rain and flooding.

Video: Understanding tropical cyclone categories

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Tropical cyclone categories

Category 1

• Damaging winds. Negligible house damage. Damage to some crops, trees and caravans. Craft may drag moorings.
• Maximum mean wind speed 63–88 km/h.
• Typical strongest gust is up to 125 km/h.

Category 2

• Destructive winds. Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small craft may break moorings.
• Maximum mean wind speed 89–117 km/h.
• Typical strongest gust 125–164 km/h.

Category 3

• Very destructive winds. Some roof and structural damage. Some caravans destroyed. Significant damage to crops and trees. Power failures likely.
• Maximum mean wind speed 118–159 km/h.
• Typical strongest gust 165–224 km/h.

Category 4

• Significant roofing loss and structural damage. Many caravans destroyed and blown away. Extensive damage to vegetation. Dangerous airborne debris. Widespread power failures.
• Maximum mean wind speed 160–199 km/h.
• Typical strongest gust 225–279 km/h.

Category 5

• Extremely dangerous with widespread destruction of buildings and vegetation.
• Maximum mean wind speed greater than 200 km/h.
• Typical strongest gust greater than 279 km/h.

Impact and effects of tropical cyclones

Tropical cyclones of any size can be dangerous.

They can produce extreme winds, heavy rain with flooding and damaging storm surge that can inundate low-lying coastal areas.

Even when a tropical cyclone weakens to a tropical low, it can bring dangerous conditions.

Wind

Tropical cyclones have gale force winds. The most powerful winds are near the centre, reaching more 90 km/h. In the most severe cyclones, gusts can exceed 280 km/h. These winds can cause extensive property damage. They can turn airborne debris into potentially lethal missiles.

When the eye of a cyclone passes over a location, there will be a temporary lull in the wind. This is soon replaced by destructive winds from another direction.

Damaging winds from a cyclone can extend a long way from the centre of the cyclone location or track. This can be up to several hundred kilometres for large and intense cyclones.

Rain

Heavy rainfall associated with a tropical cyclone can produce extensive flooding. The heavy rain can persist as the cyclone moves inland and weakens into a low pressure system. This means flooding can happen a long way from where the cyclone made landfall.

Storm surge

A tropical cyclone can cause the sea to rise well above the highest tide levels of the year when it comes ashore. These storm surges are caused mainly by strong onshore winds and reduced atmospheric pressure.

Potentially, the storm surge is the most dangerous hazard associated with a tropical cyclone. It is not the same as a tsunami. Find out more about storm surge.

Current tropical cyclones

See our Tropical cyclone forecast page.