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http://www.wmo.int/pages/mediacentre/factsheet/tropicalcyclones.html

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:

•

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.”

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:

•

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.

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:

http://www.wmo.int/pages/prog/www/tcp/Storm-naming.html

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?

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WMO Tropical Cyclone Programme:

http://www.wmo.int/pages/prog/www/tcp/index_en.html

•

Detailed information on tropical cyclones is available at the Severe Weather
Information Centre.

www.severe.worldweather.wmo.int

. This specialized WMO

web site gives real-time information on tropical cyclones and severe weather
around the world. It is maintained by the Hong Kong Observatory (HKO) in
Hong Kong, China, under the auspice of WMO.

•

The WMO World Weather Information Service

http://worldweather.wmo.int/

web site offers the latest weather forecasts of selected cities worldwide issued
by the National Meteorological and Hydrological Services of WMO Member

States and Territories. To date, 118 Members supply official weather forecasts
for 127 cities.

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For further information about severe weather, storm surge and related

disaster preparedness advisories in a specific place, please consult the
National Weather Services:

http://www.wmo.int/pages/members/members_en.html

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The Saffir-Simpson Hurricane wind scale:

http://www.nhc.noaa.gov/aboutsshs.shtml

Region-specific information:

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Caribbean Sea, Gulf of Mexico, North Atlantic and eastern North Pacific
Oceans: RSMC Miami-Hurricane Center/NOAA/NWS National Hurricane

Center, USA.

http://www.nhc.noaa.gov/index.shtml

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Western North Pacific Ocean and South China Sea: RSMC Tokyo-Typhoon
Center/Japan Meteorological Agency.

http://www.jma.go.jp/en/typh/

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Bay of Bengal and the Arabian Sea: RSMC-tropical cyclones New Delhi/India

Meteorological Department.

http://www.imd.gov.in

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South-West Indian Ocean: RSMC La Reunion-Tropical Cyclone Centre/Meteo-
France.

http://www.meteo.fr/temps/domtom/La_Reunion/

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South-West Pacific Ocean: RSMC Nadi-Tropical Cyclone Centre/Fiji

Meteorological Service.

http://www.met.gov.fj/advisories.html

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Central North Pacific Ocean: RSMC Honolulu-Hurricane Center/NOAA/NWS,
USA.

http://www.prh.noaa.gov/hnl/cphc/

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South-East Indian Ocean: TCWC-Perth/Bureau of Meteorology (Western

Australia region), Australia; and Arafura Sea and the Gulf of Carpenteria:

TCWC-Darwin/Bureau of Meteorology, Australia.

http://www.bom.gov.au/weather/cyclone/

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Coral Sea: TCWC-Brisbane/Bureau of Meteorology, Australia.

http://www.bom.gov.au/weather/cyclone/

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Tasman Sea: TCWC-Wellington/Meteorological Service of New Zealand, Ltd.

http://www.metservice.co.nz/forecasts/severe_weather.asp

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TCWC-Jakarta/ Indonesian Meteorological and Geophysical Agency,
Indonesia:

http://www.bmg.go.id

___________________________________________________________________

WMO is the United Nations' authoritative voice on weather, climate and

water

For more information please contact:

Ms Carine Richard-Van Maele, Chief, Communications and Public Affairs, WMO. Tel.:
+41 (0)22 730 83 15;

cpa[at]wmo.int

Ms Gaëlle Sévenier, Press Officer, Communications and Public Affairs, Tel. +41 (0)
22 730 8417. E-mail:

gsevenier@wmo.int

Web site:

http://www.wmo.int