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.
Tropical cyclones can last for a week or more; therefore there can be more than one cyclone at a time. Weather forecasters give each tropical cyclone a name to avoid confusion. Each year, tropical cyclones receive names in alphabetical order. Women and men's names are alternated. The name list is proposed by the National Meteorological and Hydrological Services (NMHSs) of WMO Members of a specific region, and approved by the respective tropical cyclone regional bodies at their annual/bi-annual sessions. Nations in the western North Pacific began using a new system for naming tropical cyclones in 2000. Each of the fourteen nations affected by typhoons submitted a list of names totalling 141. The names include animals, flowers, astrological signs, a few personal names are used in pre-set order. In 2010, the first hurricane in the Caribbean Sea, Gulf of Mexico and the North Atlantic region will be called Alex, and in Eastern North Pacific, it will be Agatha. For more information, see WMO website on storm naming:
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.
The worst recent tropical cyclones include Hurricane Mitch (Honduras) in 1998, Hurricane Katrina (USA) in 2005 and severe cyclone Nargis (Myanmar) in 2008.
Within the past five years, Cyclone Yasi caused property damage of more than US$ 1 billion in Australia in 2011. The worst cyclone of that year in terms of humanitarian impact was Washi, which caused extreme flooding in northern Mindanao in the Philippines in December, resulting in over 1 000 deaths and the displacement of almost 300 000 people.
Hurricane Sandy was the most noteworthy Atlantic storm of 2012. Sandy wreaked havoc across the Caribbean, claiming the lives of nearly 100 people. The strong winds and heavy downpours brought by the storm significantly damaged infrastructure, roads and thousands of homes across parts of the Caribbean. The contiguous United States was also affected, prompting severe floods across the north-east and resulting in over 130 fatalities.
In 2013, Typhoon Haiyan (named Yolanda in the Philippines) became one of the strongest storms on record to ever make landfall anywhere on the globe, with maximum 10-minute wind speeds reaching 230 km/h prior to landfall. Damage caused by immediate surge and following inundation was the worst in the past several decades, with more than 6 200 deaths and about 14 million people affected, according to reports from the United Nations Office for the Coordination of Humanitarian Affairs.
In 2013, Cyclone Phailin, the second strongest tropical cyclone to strike India since modern records began, forced 1.1 million residents in Odisha and Andhra Pradesh states to be evacuated ahead of the storm, one of the largest such evacuations in the history of India.
In 2015, Tropical cyclone Pam hit the SouthWest Pacific and made landfall over Vanuatu as a Category 5 cyclone and destroyed many homes and caused widespread devastation. Patricia was the strongest hurricane on record in either the Atlantic or eastern North Pacific basins, with maximum sustained wind speeds of 346 km/h. It made landfall on the Mexican coast in October with 241 km/h winds in a sparsely populated area. In November, Yemen witnessed unprecedented back-to-back cyclones Chapala and Megh causing substantial flooding in an extremely arid area.
WMO maintains rotating lists of names which are appropriate for each Tropical Cyclone basin. If a cyclone is particularly deadly or costly, then its name is retired and replaced by another one.
ESCAP/WMO: Tropical Cyclone Hazard Video on "Typhoon Warnings"
To promote public awareness on typhoon-related hazards, the Hong Kong Observatory (HKO) is leading a Disaster Risk Reduction (DRR) project under United Nations Economic and Social Commission for Asia and the Pacific (ESCAP)/WMO Typhoon Committee, to produce a short video on the impact of typhoons, including high winds and waves, heavy rain and storm surge. The objective is to make the information more understandable to the public and make them react through the visual impacts of short video.