Naming Tropical Cyclones

Storms that reach tropical storm strength are given names, to assist in recording insurance claims, to assist in warning people of the coming storm, and to further indicate that these are important storms that should not be ignored. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. The lists are decided upon, depending on the regions, either by committees of the World Meteorological Organization (called primarily to discuss many other issues), or by national weather offices involved in the forecasting of the storms.

Every year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place.

Naming Schemes

In the North Atlantic and Northeastern Pacific regions, feminine and masculine names are alternated in alphabetic order during a given season. The gender of the season's first storm also alternates year to year. Six lists of names are prepared in advance, and each list is used once every six years. Five letters - "Q," "U," "X," "Y" and "Z" - are omitted in the North Atlantic; only "Q" and "U" are omitted in the Northeastern Pacific. This allows for 21 names in the North Atlantic and 24 names in Northeastern Pacific. Names of storms may be retired by request of affected countries if they have caused extensive damage. The affected countries then decide on a replacement name of the same gender, and if possible, the same language as the name being retired. If there are more than 21 named storms in an Atlantic season or 24 named storms in an Eastern Pacific season, the rest are named as letters from the Greek alphabet. This was first necessary during the 2005 season when the list was exhausted. There is no precedent for a storm named with a Greek letter causing enough damage to justify retirement; and how this situation would be handled is as present unknown.

In the Central North Pacific region, the name lists are maintained by the Central Pacific Hurricane Center in Honolulu, Hawaii. Four lists of Hawaiian names are selected and used in sequential order without regard to year.

In the Northwestern Pacific, name lists are maintained by the WMO Typhoon Committee. Five lists of names are used, with each of the 14 nations on the Typhoon Committee submitting two names to each list. Names are used in the order of the countries' English names, sequentially without regard to year. Since 1981, the numbering system had been the primary system to identify tropical cyclone among Typhoon Committee members and it is still in use. International numbers are assigned by Japan Meteorological Agency on the order that a tropical storm forms while different internal numbers may be assigned by different NMCs. The Typhoon "Songda" in September 2004 was internally called the typhoon number 18 in Japan but typhoon number 19 in China. Internationally, it is recorded as the TY Sonda (0418) with "04" taken from the year. Names are rarely retired from these lists, and only at the request of the nation that submitted the name.

The Australian Bureau of Meteorology maintains three lists of names, one for each of the Western, Northern and Eastern Australian regions. These lists are in alphabetical order and alternate gender, but are used sequentially rather than switched each year. There are also Fiji region and Papua New Guinea region names.

The Seychelles Meteorological Service maintains a list for the Southwestern Indian Ocean. There, a new list is created each year, so names are not retired.

Renaming of Tropical Cyclones

In most cases, a tropical cyclone retains its name throughout its life. However, a tropical cyclone may be renamed in several occasions.

Occasion 1

A tropical storm enters the southwestern Indian Ocean from the east.

In the southwestern Indian Ocean, Meteo France in Reunion names a tropical storm once it crosses 90°E from the east, even though it has been named. In this case, the Joint Typhoon Warning Center (JTWC) will put two names together with a hyphen. Examples include Cyclone Adeline-Juliet in early 2005 and Cyclone Bertie-Alvin in late 2005.

Occasion 2

A tropical storm crosses from the Atlantic into the Pacific, or vice versa, before 2001.

It was the policy of National Hurricane Center (NHC) to rename a tropical storm which crossed from Atlantic into Pacific, or vice versa. Examples include Hurricane Cesar-Douglas in 1996 and Hurricane Joan-Miriam in 1988.

In 2001, when Iris moved across Central America, NHC mentioned that Iris would retain its name if it regenerated in the Pacific. However, the Pacific tropical depression developed from the remnants of Iris was called Fifteen-E instead. The depression later became tropical storm Manuel.

NHC explained that Iris had dissipated as a tropical cyclone prior to entering the eastern North Pacific basin; the new depression was properly named Fifteen-E, rather than Iris.

In 2003, when Larry was about to move across Mexico, NHC attempted to provide greater clarity:

"Should Larry remain a tropical cyclone during its passage over Mexico into the Pacific, it would retain its name. However, a new name would be given if the surface circulation dissipates and then regenerates in the Pacific."

Up to now, there has been no tropical cyclone retaining its name during the passage from Atlantic to Pacific, or vice versa.

Occasion 3

Uncertainties of the continuation.

When the remnants of a tropical cyclone redevelop, the redeveloping system will be treated as a new tropical cyclone if there are uncertainties of the continuation, even though the original system may contribute to the forming of the new system. One example is Tropical Depression 10-Tropical Depression 12 (which became Hurricane Katrina) from 2005.

Occasion 4

Human errors.

Sometimes, there may be human faults leading to the renaming of a tropical cyclone. This is especially true if the system is poorly organized or if it passes from the area of responsibility of one forecaster to another. Examples include Tropical Storm Ken-Lola in 1989 and Tropical Storm Upana-Chanchu in 2000.