TROPICAL CYCLONES: QUESTIONS AND ANSWERS
Hurricanes, cyclones and typhoons are tropical cyclones with maximum sustained wind speed exceeding 119 km/h near their centres, and every year responsible of thousands of victims. Although loss of lives from tropical cyclones has significantly decreased over the last decades, economic losses have increased substantially. The decrease in fatalities is, at a large extent, attributed to the improvement in the tropical cyclones forecasting and early warning systems. The World Meteorological Organization (WMO) Tropical Cyclone Programme is aimed to establish national and regionally coordinated systems to ensure that the loss of lives and damage caused by tropical cyclones are reduced to a minimum.
What is the difference between “hurricane”, “cyclone” and “typhoon”?
"Hurricane", "cyclone" and "typhoon" are different terms for the same weather phenomenon which is accompanied by torrential rain and maximum sustained wind speeds (near centre) exceeding 119 kilometers per hour:
When do tropical cyclones occur?
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.
What is the connection between tropical cyclones and wind speed?
Depending on the maximum sustained wind speed, tropical cyclones will be designated as follows:
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:
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.
How are tropical cyclones named?
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:
How are tropical cyclones predicted?
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.
Where did tropical cyclones occur recently?
Between 1886 and 1998, out of the 566 Atlantic hurricanes in the Atlantic, twenty two have grown as strong as to become Category 5 hurricanes with maximum sustained wind speeds exceeding 249 km/h. The worst recent tropical cyclones include Hurricane Mitch (Honduras) in 1998, Hurricane Katrina (USA) in 2005 and most recently hurricane Gustav (Haiti) in 2008, and severe cyclone Nargis (Myanmar) in 2008.
In 2008, a total of sixteen named tropical cyclones formed in the Atlantic including eight hurricanes, five of which were major hurricanes at Category 3 or higher on the Saffir-Simpson Hurricane Scale. These numbers are well above the long-term averages of 11, 6, and 2 respectively. The 2008 Atlantic hurricane season was devastating, with casualties and widespread destruction in the Caribbean, Central America and the United States of America. For the first time on record, six consecutive tropical cyclones (Dolly, Edouard, Fay, Gustav, Hanna and Ike) made landfall on the United States of America, and two major hurricanes (Gustav and Ike) hit Cuba.
In the East Pacific, sixteen named tropical cyclones were recorded in 2008, of which seven evolved into hurricanes and two of them into major hurricanes at Category 3 or higher. In the Western North Pacific, twenty two named tropical cyclones were recorded in 2008, ten of which were classified as typhoons compared to the long-term average of twenty seven and fourteen, respectively.
As of early November 2009, the hurricane season in the Atlantic counts nine named tropical cyclones, of which three became hurricanes. These numbers are well below the long term average of tropical cyclones in the region.
The Western North Pacific has been hit several times in September - October 2009 by numerous typhoons such as Ondoy, Ketsana, Parma, Lupit and Mirinae, causing many casualties.
Where do I find more information?
WMO is the United Nations' authoritative voice on weather, climate and water
Web site: http://www.wmo.int
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