These giant, dangerous storms often cause substantial destruction.
Earth Science, Meteorology
The names of the powerful storms that form in the waters of the Atlantic and Pacific—whether hurricane, cyclone, or typhoon—depends on where they form. Tropical Cyclone Amanda was a category 4 on the Saffir-Simpson scale imaged by NASA’s Aqua satellite.
NASA image from Jeff Schmaltz
Centuries ago European explorers learned the indigenous word hurakan, signifying evil spirits and weather gods, to describe the storms that battered their ships in the Caribbean. Today, " hurricane " is one of three names for giant, spiraling tropical storms with winds of at least 119 kilometers (74 miles) an hour.
Called hurricanes when they develop over the North Atlantic, central North Pacific, and eastern North Pacific, these rotating storms are known as cyclones when they form over the South Pacific and Indian Ocean, and typhoons when they develop in the Northwest Pacific.
Whatever the moniker, tropical cyclones can annihilate coastal areas and cause massive death tolls. Rated on the five-point Saffir-Simpson scale based on wind speed, hurricanes are considered major when they reach category 3. A category 5 storm can deliver wind speeds of more than 253 kilometers (157 miles) an hour.
The Atlantic Ocean’s hurricane season peaks from mid-August to late October and averages five to six hurricanes per year. While cyclones on the northern Indian Ocean typically form between April and December, with peak storm activity around May and November.
How Are Hurricanes Formed?
Hurricanes begin as tropical disturbances in warm ocean waters with surface temperatures of at least 26.5 degrees Celsius (80 degrees Farenheit). Those low-pressure systems are fed by energy from warm seas.
A storm with wind speeds of 61 kilometers (38 miles) an hour or less is classified as a tropical depression. It becomes a tropical storm—and is given a name, according to conventions determined by the World Meteorological Organization—when its sustained wind speeds top 63 kilometers (39 miles) an hour.
Hurricanes are enormous heat engines that deliver energy on a staggering scale. They draw heat from warm, moist ocean air and release it through condensation of water vapor in thunderstorms.
Hurricanes spin around a low-pressure center known as the eye. Sinking air makes this 32- to 64-kilometer (20- to 40-mile)-wide area notoriously calm. But the eye is surrounded by a circular “eye wall” that contains the storm’s strongest winds and rain.
Hurricane Dangers
Hurricanes bring destruction ashore in many different ways. When a hurricane makes landfall, it often produces a devastating storm surge —ocean water pushed ashore by wind—that can reach six meters (20 feet) high and move several kilometers inland.
Storm surges and flooding are the two most dangerous aspects of hurricanes, accounting for three-quarters of deaths from Atlantic tropical cyclones, according to a 2014 study. A third of the deaths from Hurricane Katrina, which made landfall off the coast of Louisiana in 2005 and killed approximately 1,200 people, were caused by drowning. Katrina is also the costliest hurricane on record, with damage totaling $125 billion.
A hurricane’s high winds are destructive and may spawn tornadoes. Torrential rains cause further damage via flooding and landslides, which may occur many kilometers inland.
Although extremely potent storms have formed in the Atlantic, the most powerful tropical cyclones on record have formed in the Pacific, which gives storms more room to grow before they make landfall. Hurricane Patricia, which formed in the eastern Pacific off Guatemala in 2015, had the strongest winds recorded, at 346 kilometers (215 miles) an hour. The strongest Atlantic storm was Wilma in 2005, with winds of 294 kilometers (183 miles) an hour.
The best defense against a hurricane is an accurate forecast that gives people enough time to get out of the way. The United States National Hurricane Center issues hurricane watches for possible storms within 48 hours and hurricane warnings for expected storms within 36 hours.
Hurricanes and Climate Change
Climate change may be driving more frequent, more intense extreme weather, and that includes hurricanes. The 2018 hurricane season was one of the most active on record, with 22 major hurricanes in the Northern Hemisphere in under three months, and 2017 also saw seriously devastating Atlantic storms. While a number of factors determine a hurricane's strength and impact, warmer temperatures in certain locations play an important role. In the Atlantic, warming in the Arctic could drive future hurricane tracks farther west, making a U.S. landfall more likely.
Hurricane Harvey, which dropped a record-breaking 131.6 centimeters (51.8 inches) of rain on southeastern Texas in 2017, was fueled by surface waters in the Gulf of Mexico that were 1.11 degrees Celsius (2 degrees Fahrenheit) warmer than three decades before. A warmer atmosphere can also furnish more water vapor for making rain, as evaporation increases and warm air holds more vapor than cold.
Warming temperatures can also slow tropical cyclones, which can be a problem if their progression over land is extended, potentially increasing storm surges, rainfall, and exposure to high winds.
Potential trends make it more important than ever to be prepared for coming storms and to address the root causes of climate change, scientists say.
