The idea of naming something large and impersonal like a storm may seem a strange thing to do. But the reason why tropical cyclones are named isn't much different than why people or pets are--it helps distinguish one from another.
While the practice of naming storms itself has been around for hundreds of years, the rules used for arriving at these names has varied greatly.
History of Hurricane Naming
During the 1800s and early 1900s, storms were "unofficially" named. That is to say, they frequently took their titles from the locations they affected, the saint's day or holiday on which they occurred, or the geographic coordinates (latitude/longitude) where they were positioned. Sometimes, they were simply numbered (Hurricane One, Two, Three, etc.).
At the end of the 19th century, storms began taking female names. (Australian meteorologist Clement Wragge is credited with starting this.) While this practice became widespread during World War II, it was never recognized by the weather community as the official way of naming storms.
It wasn't until 1947 that the United States established its first official hurricane naming guidelines. These stated that all tropical storms and hurricanes would be named using the phonetic alphabet (Alpha, Beta, Charlie, etc.). These guidelines were replaced by the official use of female names only in 1953. By 1979, male names were added, meaning both genders were represented on names lists for the Atlantic and Eastern Pacific oceans. (That's right, the current practice of using male and female first names didn't happen until as recently as 1979!)
How Names are Chosen
Originally, the NOAA National Hurricane Center (NHC) was responsible for assigning storm titles, however, in 1977, NOAA relinquished control over the name selection process. Following this, the World Meteorological Organization (WMO) assumed the responsibility.
The WMO Hurricane Committee assigns storm names six lists at a time. Rather than assign new names every year, these same six lists are recycled every six years. (This means that names used in 2013 will be used again in 2019, and so on. If you've ever noticed This is why it's considered proper hurricane etiquette to not only state the name, but also the season year in which a storm occurred.)
The only time name lists are revised is when a past storm is considered too costly or life-threatening that using its name again would be insensitive. In this case, the offending name is "retired," or removed from the names list, and another name of the same letter and gender is substituted.
When are Tropical Cyclones Named?
When an area of tropical activity reaches Once a tropical depression's maximum sustained winds strengthen to between 39-73 mph, it becomes a tropical storm. It is at this time that the storm receives a formal name, thus becoming a named storm. Each subsequent storm is given the next available name on the list.
What Happens if All Twenty-One Names are Used?
When all 21 letters have been exhausted, any additional storms are named using the Greek alphabet.
What if a Tropical Cyclone Forms Outside of the Season Timeframe?
If a tropical storm or hurricane develops outside of the June 1 to November 30 period, it'll receive the next available name from the list of the same year as the storm's formation date. For example, a tropical cyclone forming in December 2012 would take its name from the 2012 list, while a tropical storm forming in May of 2013 (pre-season) would take its name from the 2013 names list.