WASHINGTON—Look, it’s a hurricane! It’s a cyclone! No, it’s a typhoon!

A powerful typhoon hit the Philippines on Friday and moved out to the West Philippine Sea (South China Sea).

Hurricane? Cyclone? Typhoon? They’re all the same—officially tropical cyclones. But they just use distinctive terms for a storm in different parts of the world.

Hurricane is used in the Atlantic, Caribbean Sea and central and northeast Pacific. They are typhoons in the northwest Pacific. In the Bay of Bengal and the Arabia Sea, they are called cyclones. Tropical cyclone is used in the southwest Indian Ocean; in the southwestern Pacific and southeastern Indian Ocean, they are severe tropical cyclones.

Strength: A storm gets a name and is considered a tropical storm at 63 kilometers per hour. It becomes a hurricane, typhoon, tropical cyclone or cyclone at 119 kph. There are five strength categories, depending on wind speed. The highest category is 5 and that’s above 249 kph. Australia has a different system for categorizing storm strength.

Rotation: If they are north of the equator, they rotate clockwise. If they are south, they rotate counterclockwise.

Season: The Atlantic and central Pacific hurricane seasons are from June 1 to Nov. 30. Eastern Pacific: May 15 to Nov. 30; northwestern Pacific season is close to all year, with the most from May to November. The cyclone season in the south Pacific and Australia runs from November to April. The Bay of Bengal has two seasons, from April to June and September to November.

Busiest place

Where is the busiest place? The northwestern Pacific where Supertyphoon “Haiyan” has just hit. A normal year there involves 27 named storms. Haiyan is the 28th named storm and there has already been a 29th. By comparison, the Atlantic averages 11 named storms a year and this year there have been 12, none of them causing major problems.

Who decides the names? The lists are maintained by the World Meteorological Organization; the names are ones that are familiar in each region. Names are taken off the list and replaced to avoid confusion if a hurricane causes a lot of damage or deaths. For example, Katrina was retired after it devastated New Orleans in 2005. The Philippines has its own naming system, so Haiyan is also being called “Yolanda.”

How does El Niño affect storms? During an El Niño—when the central Pacific is warming—there are fewer Atlantic storms. El Niños shift where storms form, but not the number, for the northwest Pacific and the southwest Pacific. The central Pacific gets more storms during El Niño and the year after. This year has neither an El Niño nor its opposite, a La Niña. It is a neutral year. AP

Sources: World Meteorological Organization, National Oceanic and Atmospheric Administration, and Weather Underground