When one of the deadliest storms ever recorded in the Southern Hemisphere roared through Mozambique, Malawi and Zimbabwe in March, it was called Cyclone Idai. But the big blow that sideswiped Guam in February was Typhoon Wutip. And if the swirl of nasty weather coalescing over the Gulf of Mexico strengthens as expected this week, it will be Tropical Storm (or maybe even Hurricane) Barry.

What makes a major storm a hurricane, a typhoon or a cyclone? It comes down to location.

They all refer to tropical cyclones — circular storms that form over warm waters, with very low air pressure at the center and winds greater than 74 miles an hour. But different terms are used for such storms in different parts of the world.

The word hurricane is used for the ones that form in the North Atlantic, the northeastern Pacific, the Caribbean Sea or the Gulf of Mexico. Typhoons are storms that develop in the northwestern Pacific and usually threaten Asia.

The international date line serves as the Pacific Ocean’s dividing marker, so when a hurricane crosses over it from east to west, it becomes a typhoon instead, and vice versa.

The same kinds of storms in the Southern Hemisphere are easier to keep straight. In the southern Indian Ocean or the South Pacific, they are tropical cyclones or severe tropical cyclones. In the Bay of Bengal or Arabian Sea, both in the northern Indian Ocean, they are simply called cyclones.

As violent as they are, these storms help to regulate the global climate, by moving heat energy away from the tropics and toward the poles.

To every storm there is a season

Aside from having different names, hurricanes, typhoons and cyclones also have different seasons. The Atlantic hurricane season officially runs from June 1 to Nov. 30. The Pacific season starts slightly earlier. Typhoons can form year-round, but are most common from May to October. The next cyclone season in the South Pacific will begin on Nov. 1 and end on April 30, 2020.

In the southern Indian Ocean, the season begins two weeks later and ends at the same time, except in the island nations of Mauritius and the Seychelles, where it extends to May 15. Cyclones in the northern Indian Ocean have no official season, but tend to be concentrated from May to November.

Whatever they’re called, tropical cyclones generally become weaker after they arrive on land, since they draw their energy from the evaporation of water in the oceans below them. But they can travel quite far inland before they dissipate, wreaking havoc through wind damage, torrential rains and flooding.

[Read our tips for protecting your home if you have to evacuate.]

Storms whose winds are not quite strong enough to qualify as tropical cyclones are called tropical storms if their sustained winds are 39 to 73 miles an hour, or tropical depressions (a reference to the low pressure at their core) below that range.

Tropical cyclones around the world are named according to a list maintained by the World Meteorological Organization. The names of the deadliest storms, like Typhoon Haiyan or Hurricane Katrina, are retired.

Grading a storm’s intensity

Hurricanes are rated in categories from 1 to 5 according to the Saffir-Simpson scale, which is based on sustained wind speed. According to the National Hurricane Center, storms in Category 3 or higher, which have wind speeds of at least 111 miles per hour, “are considered major hurricanes because of their potential for significant loss of life and damage.”

Typhoons are monitored by the Japan Meteorological Agency, which also rates them by sustained wind speed; it uses three classifications, “typhoon,” “very strong typhoon” or “violent typhoon.”

The Joint Typhoon Warning Center, a United States military command in Pearl Harbor, Hawaii, also issues storm advisories using the designations “tropical depression,” “tropical storm,” “typhoon” and “super typhoon.”

Cyclones in the Indian Ocean are classified according to two intensity scales, depending on where they are, with terms like “very intense tropical cyclone” and “super cyclonic storm.” Australia rates cyclones much the way North America rates hurricanes, in categories from 1 to 5.

Where did all these terms come from?

Storm terminology has been highly influenced by the histories and cultural interactions of different regions.

“Hurricane” appeared in English in the 16th century as an adaptation of the Spanish word “huracán.” “Typhoon” is variously described as coming from Arabic (“tafa”) or Chinese (“taifeng”), perhaps both. “Cyclone” was coined in the late 18th century by a British official in India, from the Greek for “moving in a circle.”

But a storm by any other name should still be taken seriously.

Hanah Jun and Patrick J. Lyons contributed reporting.

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