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: Tropical cyclones – impacts and warnings
All tropical cyclones are dangerous. They can cause large-scale destruction and pose serious risk to people's safety. It's important to understand their impacts, and to know about our warning services so you can take action before the severe weather impacts you.
Tropical cyclones are powerful storms that can bring destructive winds, heavy rain, flooding, large waves and coastal erosion. They can also cause devastating flooding from storm surge, when sea water is pushed onto coastal areas.
Even when a tropical cyclone is downgraded to a tropical low, flooding from heavy rain can still create dangerous conditions. They can also track inland or south, bringing floods that can isolate remote communities. Roads can be cut off, making it hard to access essential services.
We update our tropical cyclone 7-day forecast at least twice daily. It shows where any tropical lows are and the chance they could be a cyclone at each time step. When there's a threat to communities from a tropical cyclone, we issue a track map showing its likely path and strength. We issue a tropical cyclone watch when gales are forecast to reach land in the next 48 hours. We issue a tropical cyclone warning when gales are expected to reach land within 24 hours.
Tropical cyclones can get stronger fast. We use a scale of 1 to 5 to rank the wind strength of a cyclone, with category 5 being the strongest.
A category 1 tropical cyclone has wind gust speeds up to 125 kilometres per hour.
A category 2 tropical cyclone has gusts between 125 and 164 kilometres per hour. These winds can damage houses and blow over large trees. It can be dangerous to be outside.
A category 3 cyclone is called 'severe', with gusts reaching between 165 and 224 kilometres per hour. These winds can damage roofs and buildings, destroy caravans and cause power failures. They can hurl large objects through the air.
At category 4, wind gusts reach between 225 and 279 kilometres per hour. They can rip roofs off buildings and cause structural damage and widespread power failures.
A category 5 tropical cyclone has gusts of 280 kilometres per hour or more. These are extremely dangerous and cause large-scale destruction and risk to life.
Tropical cyclones are dangerous no matter what category. Heavy rain and flooding can have severe impacts however strong the winds are. Make your plans to evacuate or take shelter well before a cyclone is predicted to arrive.
For the latest information check the Bureau's website. Download the BOM Weather app and set warning notifications for your location. And always follow the advice from your local emergency services.
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.