Tropical cyclone categories

Learn about tropical cyclone categories, severity and impact

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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

The northern coastline of Australia is one of the most cyclone-prone areas of the world.

Communities in the region are threatened by tropical cyclones every season, with a very real risk to property and life. A tropical cyclone’s effects vary depending on its intensity, so it’s important you understand the hazards involved and the potential damage a tropical cyclone can cause. The intensity of tropical cyclones is described according to the numerical scale of 1 to 5, with 5 being the highest rating.

These intensity ratings are based on the maximum wind gusts associated with the cyclone, which usually occur around the centre, known as the eye.

Tropical cyclones can intensify rapidly. There have even been occasions when a category 1 cyclone has become a category 5 within a day. It’s essential that your plans to evacuate or take shelter are made well before the predicted arrival of the strongest winds.

A Category 1 tropical cyclone has estimated wind gusts up to 125 km/h. These wind speeds can damage crops, blow over small unsecured objects and cause boats to drag their moorings.

A Category 2 cyclone has estimated gusts between 125 and 164 km/h. These wind speeds will cause damage to homes, blow over large trees and make it dangerous to be outside.

A Category 3 cyclone has estimated gusts between 165 and 224 km/h. These destructive wind gusts can rip roofing from buildings, destroy caravans, cause large debris to fly through the air; and the risk of injury is real. If a cyclone reaches category 3 intensity, it is referred to as a severe tropical cyclone and is often the point when the characteristic eye of a cyclone will become clear on satellite images.

A Category 4 cyclone has estimated gusts of between 225 and 279 km/h. These winds are very destructive, causing significant roofing and structural damage to buildings, dangerous airborne debris and widespread power failures.

A Category 5 cyclone has estimated gusts of 280 km/h and above. Winds at this speed are extremely dangerous and cause widespread destruction.

Along with powerful winds, tropical cyclones can bring heavy rain and storm surge, creating life-threatening situations in addition to the cyclone itself. Heavy rainfall can cause flooding, and it’s not always the case that the most intense cyclones bring the heaviest rainfall. Storm surges associated with cyclones can have dangerous and devastating effects on coastal areas, with the level of inundation highly dependent on the tide levels around the time the cyclone crosses the coast.

All tropical cyclones are dangerous, regardless of their category; so be prepared, listen to local authorities and stay updated via the Bureau's website. Then you always have the latest cyclone information.

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 and storm tides on our Tides and sea level page.

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