FAQs - Tropical Cyclones

Hurricane, cyclone and typhoon are different terms for the same weather phenomenon: torrential rain and maximum sustained wind speeds (near centre) exceeding 119 kilometers per hour:

• In the western North Atlantic, central and eastern North Pacific, Caribbean Sea and Gulf of Mexico, such a weather phenomenon is called "hurricanes".
• In the western North Pacific, it is called "typhoons"
• In the Bay of Bengal and Arabian Sea, it is called "cyclones"
• In western South Pacific and southeast India Ocean, it is called “severe tropical cyclones”
•  In the southwest India Ocean, it is called “tropical cyclones”

The typhoon season in the western North Pacific region typically runs from May to November. The Americas/Caribbean hurricane season runs from June 1 to November 30, peaking in August and September. The cyclone season in South Pacific and Australia normally runs from November to April. In the Bay of Bengal and Arabian Sea, tropical cyclones usually occur from April to June, and September to November. The East Coast of Africa normally experiences tropical cyclones from November to April.

Depending on the maximum sustained wind speed, tropical cyclones will be designated as follows:

• It is a tropical depression when the maximum sustained wind speed is less than 63 km/h.
• It is a tropical storm when the maximum sustained wind speed is more than 63 km/h. It is then also given a name.
• Depending on the ocean basins, it is designated either a hurricane, typhoon, severe tropical cyclone, severe cyclonic storm or tropical cyclone when the maximum sustained wind speed is more than 119 km/h.

Tropical cyclones can be hundreds of kilometers wide and can bring destructive high winds, torrential rain, storm surge and occasionally tornadoes. According to the Saffir-Simpson Hurricane Wind Scale, the hurricane strength varies from Category 1 to 5:

• Category 1 hurricane is referring to the hurricane with maximum sustained wind speeds of 119-153 km/h.
• Category 2 hurricane is referring to the hurricane with maximum sustained wind speeds of 154-177 km/h.
• Category 3 hurricane is referring to the hurricane with maximum sustained wind speeds of 178-209 km/h.
• Category 4 hurricane is referring to the hurricane with  maximum sustained wind speeds of 210-249 km/h.
• Category 5 hurricane is referring to the hurricane with maximum sustained wind speeds exceeding 249 km/h.

The impact of a tropical cyclone and the expected damage depend not just on wind speed, but also on factors such as the moving speed, duration of strong wind and accumulated rainfall during and after landfall, sudden change of moving direction and intensity, the structure (e.g. size and intensity) of the tropical cyclone, as well as human response to tropical cyclone disasters.

Meteorologists around the world use modern technology such as satellites, weather radars and computers etc. to track tropical cyclones as they develop. Tropical cyclones are often difficult to predict, as they can suddenly weaken or change their course. However, meteorologists use state-of-art technologies and develop modern techniques such as numerical weather prediction models to predict how a tropical cyclone evolves, including its movement and change of intensity; when and where one will hit land and at what speed. Official warnings are then issued by the National Meteorological Services of the countries concerned.

The WMO framework allows the timely and widespread dissemination of information about tropical cyclones. As a result of international cooperation and coordination, tropical cyclones are increasingly being monitored from their early stages of formation. The activities are coordinated at the global and regional levels by WMO through its World Weather Watch and Tropical Cyclone Programmes. The Regional Specialized Meteorological Centers with the activity specialization in tropical cyclones, and Tropical Cyclone Warning Centres, all designated by WMO, are functioning within the Organization’s Tropical Cyclone Programme. Their role is to detect, monitor, track and forecast all tropical cyclones in their respective regions. The Centres provide, in real-time, advisory information and guidance to the National Meteorological Services.