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Find even more resources on hurricanes  in our searchable resource database.

Hurricanes are one of nature’s most powerful storms. They produce strong winds, storm surge flooding, and heavy rainfall that can lead to inland flooding, tornadoes, and rip currents.

Hurricane Humberto, as captured by a NOAA satellite September 15, 2019. (Image credit: NOAA Satellites)

What is a hurricane?

Hurricanes, known generically as tropical cyclones , are low-pressure systems with organized thunderstorm activity that form over tropical or subtropical waters . They gain their energy from warm ocean waters.

As storm systems strengthen into hurricanes, the surface winds move continuously in a circular motion. Meteorologists refer to this pattern as “closed circulation." The direction of circulation is different depending on where the storm is located: it is counter-clockwise in the Northern hemisphere and clockwise in the Southern hemisphere.

These rotating winds lead to the development of the characteristic “eye” of the hurricane, the calm, clear center of the storm. The eye is surrounded by the eyewall , where winds are strongest. 

Tropical cyclones are classified by their maximum wind speed. 

• Winds less than 39 mph: Tropical depressions
• Winds 39-73 mph: Tropical storms 
• Winds 74 mph or greater: Hurricanes

Major hurricanes have winds of at least 111 mph and can reach speeds of over 180 mph, with gusts of 200 mph.   

In the rearview mirror, life-changing events can look a little different. An extreme weather event survived by a young Anthony Arguez later altered his life in a positive way. Despite the devastation, Hurricane Andrew’s landfall in the summer of 1992 sent him on a new path that led to NOAA.

What’s in a name?

Hurricanes, typhoons, and cyclones are actually all the same type of storm, but have different names based on where they form. In the North Atlantic and central and eastern North Pacific, these storms are called “hurricanes.” In the western North Pacific, they are called “typhoons” and in the South Pacific and Indian Ocean, they are called “cyclones.” (Tropical cyclones are rare in the South Atlantic.)

Once a storm escalates to tropical storm-level winds, it is given a name . The names are chosen by an international committee of the World Meteorological Organization offsite link (WMO). Names are reused every six years, although the WMO may retire the name of a particularly deadly or costly storm.

How do tropical cyclones form?

Tropical storms form from an atmospheric disturbance like a tropical wave or group of thunderstorms. For these disturbances to grow into a tropical cyclone, the following environmental conditions must be in place:

• Warm ocean waters (at least 80°F/27°C).
• An unstable atmosphere driven by differences in temperature, where temperature decreases with height.
• Moist air near the mid-level of the atmosphere.
• Must be at least 200 miles (with rare exceptions) north or south of the equator for it to spin (due to the Coriolis effect ).
• Little change in wind speed or direction with height (known as low vertical wind shear ).

Hurricane safety 

Hurricanes, tropical storms, and tropical depressions pose a variety of threats to people and property. Storm surge and inland flooding have historically been the number one offsite link and two causes of loss of life during hurricanes. Hurricanes can also bring strong winds, tornados, rough surf, and rip currents. The time to prepare for a hurricane is before hurricane season begins, June 1 in the Atlantic and May 15 in the Eastern and Central Pacific.

Hurricane categories only tell part of the story 

Hurricanes are categorized using the Saffir-Simpson Hurricane Wind Scale , which addresses wind speed on a scale from one to five. However, a tropical storm or category one or two hurricane can cause as much overall damage as a major hurricane.  

Every storm is different

Each tropical system can bring a variety of unique, life-threatening hazards to a given location. It’s critical to know your risk, especially if you live in a storm surge evacuation zone or in an area where flooding could occur. Even if you’ve previously survived a storm in your area, future hurricanes may bring different hazards.

Local officials may issue evacuation orders before storm or storm surge watches or warnings are issued for your area. Evacuation orders are released to ensure residents have enough time to leave vulnerable areas before the first hazards from the storm arrive. Be prepared to evacuate and do so immediately when ordered.

Hurricanes bring extreme rainfall 

Warm air can hold more moisture than cool air. In tropical cyclones, the air is particularly warm and can hold a tremendous amount of moisture. The moisture cools as it rises and condenses into heavy rain, often much more than a typical low pressure system offsite link . These rains can occur not only at the coast, but many miles inland , causing flooding that can continue for days or even weeks after a storm. Always follow evacuation orders and never drive into flooded roadways. If you live in a low-lying or flood prone area, always have an evacuation plan before a storm begins.

Water, not wind, is the biggest threat

Though hurricanes are well known for strong and destructive winds, hurricane storm surge is the greatest threat. Storm surge is water that is pushed toward the shore by winds swirling around the storm. This rise in water level can cause severe flooding in coastal areas. With much of the United States' densely populated Atlantic and Gulf Coast coastlines less than 10 feet above mean sea level, the danger from storm surges is tremendous. Historically, about half of direct fatalities offsite link from hurricanes that make landfall in the U.S. are from storm surge. Always follow evacuation orders.

Run from the water, hide from the wind

When you’re at risk from flooding, it’s important to get to high ground away from bodies of water and any flood-prone areas. When there are high winds, but no danger of flooding (rare in hurricanes, but also important during any storm), it’s important to shelter in place in a sturdy structure, away from doors and windows. This is why most evacuation orders are given for water, not wind.

Stay safe after a storm passes

Hurricane-related hazards don’t disappear when the weather clears. After the storm , use generators safely, be careful not to overexert yourself, and do not venture into storm-damaged areas before it is safe to do so. Many fatalities are reported after storms end, due to heart attacks, issues related to power outages, and accidents.

EDUCATION CONNECTION

As the climate changes, hurricane impacts also change. Coastal communities are particularly vulnerable as rising sea levels compound storm surge flooding. This collection provides educators and students with resources to explore how hurricanes form, their potential effects, ways to prepare for hurricanes, and even a citizen science project to classify hurricanes from satellite imagery.

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How do hurricanes form?

Warm ocean waters and thunderstorms fuel power-hungry hurricanes..

Hurricanes form over the ocean, often beginning as a tropical wave—a low pressure area that moves through the moisture-rich tropics, possibly enhancing shower and thunderstorm activity.

Recipe for a Hurricane

Whipping up a hurricane calls for a number of ingredients readily available in tropical areas:

• A pre-existing weather disturbance : A hurricane often starts out as a tropical wave.
• Warm water : Water at least 26.5 degrees Celsius over a depth of 50 meters powers the storm.
• Thunderstorm activity : Thunderstorms turn ocean heat into hurricane fuel.
• Low wind shear : A large difference in wind speed and direction around or near the storm can weaken it.

Mix it all together, and you’ve got a hurricane—maybe. Even when all these factors come together, a hurricane doesn’t always develop.

Hurricanes are powerhouse weather events that suck heat from tropical waters to fuel their fury. These violent storms form over the ocean, often beginning as a tropical wave—a low pressure area that moves through the moisture-rich tropics, possibly enhancing shower and thunderstorm activity.

As this weather system moves westward across the tropics, warm ocean air rises into the storm, forming an area of low pressure underneath. This causes more air to rush in. The air then rises and cools, forming clouds and thunderstorms. Up in the clouds, water condenses and forms droplets, releasing even more heat to power the storm.

When wind speeds within such a storm reach 74 mph, it’s classified as a hurricane. The terms “hurricane” and “tropical cyclone” refer to the same kind of storm : a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has closed, low-level circulation.

During just one hurricane, raging winds can churn out about half as much energy as the electrical generating capacity of the entire world, while cloud and rain formation from the same storm might release a staggering 400 times that amount.

Did you know?

Less than one percent of algal blooms actually produce toxins. Not all algal blooms are harmful, and some may actually be beneficial. Phytoplankton are microscopic algae that form the base of the marine food web, and therefore, all other life in the ocean relies on them. Blooms can also be good indicators of environmental changes not only in the water, but also on land.

More Information

Hurricanes: Preparedness, Response, Recovery

Ocean Today: Fuel for the Storm

Why do we name tropical storms?

National Hurricane Center

Last updated:

Author: NOAA

How to cite this article

How Does a Hurricane Form?

Watch this video to learn how hurricanes form! Click here to download this video (1920x1080, 125 MB, video/mp4).

Hurricanes are the most violent storms on Earth. They form near the equator over warm ocean waters. Actually, the term hurricane is used only for the large storms that form over the Atlantic Ocean or eastern Pacific Ocean.

The generic, scientific term for these storms, wherever they occur, is tropical cyclone. Other names they are given, depending on where in the world they are born, are typhoons, cyclones, severe tropical cyclones, or severe cyclonic storms. Whatever they are called, the same forces and conditions are at work in forming these giant storms, any of which can cause damage or devastation when they hit land where people live.

Tropical cyclones are like engines that require warm, moist air as fuel. So the first ingredient needed for a tropical cyclone is warm ocean water. That is why tropical cyclones form only in tropical regions where the ocean is at least 80 degrees F for at least the top 50 meters (about 165 feet) below the surface.

The second ingredient for a tropical cyclone is wind. In the case of hurricanes that form in the Atlantic Ocean, the wind blowing westward across the Atlantic from Africa provides the necessary ingredient. As the wind passes over the ocean's surface, water evaporates (turns into water vapor) and rises. As it rises, the water vapor cools, and condenses back into large water droplets, forming large cumulonimbus clouds. These clouds are just the beginning.

NOAA's GOES-East weather satellite zoomed in on the eye of Hurricane Dorian in September 2019. Credit: NOAA

Meteorologists have divided the development of a tropical cyclone into four stages: Tropical disturbance, tropical depression, tropical storm, and full-fledged tropical cyclone.

When the water vapor from the warm ocean condenses to form clouds, it releases its heat to the air. The warmed air rises and is pulled into the column of clouds. Evaporation and condensation continue, building the cloud columns higher and larger. A pattern develops, with the wind circulating around a center (like water going down a drain). As the moving column of air encounters more clouds, it becomes a cluster of thunderstorm clouds, called a tropical disturbance.

As the thunderstorm grows higher and larger, the air at the top of the cloud column is cooling and becoming unstable. As the heat energy is released from the cooling water vapor, the air at the top of the clouds becomes warmer, making the air pressure higher and causing winds to move outward away from the high pressure area. This movement and warming causes pressures at the surface to drop. Then air at the surface moves toward the lower pressure area, rises, and creates more thunderstorms. Winds in the storm cloud column spin faster and faster, whipping around in a circular motion. When the winds reach between 25 and 38 mph, the storm is called a tropical depression.

When the wind speeds reach 39 mph, the tropical depression becomes a tropical storm. This is also when the storm gets a name. The winds blow faster and begin twisting and turning around the eye, or calm center, of the storm. Wind direction is counterclockwise (west to east) in the northern hemisphere and clockwise (east to west) in the southern hemisphere. This phenomenon is known as the Coriolis effect.

When the wind speeds reach 74 mph, the storm is officially a hurricane. The storm is at least 50,000 feet high and around 125 miles across. The eye is around 5 to 30 miles wide. The trade winds (which blow from east to west) push the hurricane toward the west—toward the Caribbean, the Gulf of Mexico, or the southeastern coast of the U.S. The winds and the low air pressure also cause a huge mound of ocean water to pile up near the eye of the hurricane, which can cause monster storm surges when all this water reaches land.

Hurricanes usually weaken when they hit land, because they are no longer being fed by the energy from the warm ocean waters. However, they often move far inland, dumping many inches of rain and causing lots of wind damage before they die out completely.

Lastly, what are the five categories of hurricanes?

Hurricane categories:

Click below to download a poster:.

What Causes Hurricanes?

Learn about these violent storms and why they’re dangerous.

Every year, coastal regions brace themselves for violent windstorms known as hurricanes. But how do these storms form and grow?

The oversimplified answer: Warm ocean water plus the Earth’s eastward rotation.

“They’re heat engines,” said meteorologist Jeff Masters of the website Weather Underground in a previous interview . “They take heat from the oceans and convert it to the energy of their winds. They’re taking thermal energy and making mechanical energy out of it.”

The natural engine that is a hurricane is fueled by warm, moist air. The storms move heat from the ocean surface high into Earth’s atmosphere. They can travel thousands of miles from the tropics toward the Earth’s poles.

According to NOAA’s National Hurricane Center , the average hurricane eye—the still center where pressure is lowest and air temperature is highest—stretches 20 to 30 miles across, with some even growing as large as 120 miles wide.

The strongest storms, equivalent to Category 5 on the Saffir-Simpson scale , have sustained winds that exceed 155 miles an hour.

Why Are Hurricanes Dangerous?

While hurricanes are categorized based on their wind speeds, wind isn’t typically the most dangerous part of such storms. “It’s the storm surge ,” said Kerry Emanuel , an atmospheric scientist at MIT, in an earlier interview. The storm surge is the bulge of water built up in front of a cyclone or hurricane courtesy of its winds.

It’s the number one killer in hurricanes, Emanuel explained. “That’s what killed people in Katrina , it’s what killed people in Sandy and in Haiyan.” (Read “Charts Show How Hurricane Katrina Changed New Orleans.” )

Emanuel likened a storm surge to a tsunami. One just happens to be caused by earthquakes (tsunamis), while the other is generated by hurricanes.

Flash flooding caused by intense rains is also a major killer, Emanuel said. “ Hurricane Mitch [in 1998] killed 12,000 people and it was all from flash flooding.”

Then comes wind that blows around debris. Hurricane Andrew in 1992 is an example of this. “It didn't really cause too much of a storm surge,” the atmospheric scientist said, “but boy did it blow a lot of buildings down.”

Climate change will likely increase the frequency of “the high-end hurricanes,” Emanuel said.

And those powerful storms have the potential to produce a lot of rain, flooding, and strong storm surges.

Is That a Hurricane or a Cyclone?

What’s the difference between hurricanes, cyclones, and typhoons ? Actually, they’re all the same weather phenomenon. Scientists just call these storms different things depending on where they occur.

In the Atlantic and northern Pacific, the storms are called hurricanes, after the Caribbean god of evil, named Hurrican.

In the northwestern Pacific, the same powerful storms are called typhoons. In the southeastern Indian Ocean and southwestern Pacific, they are called severe tropical cyclones.

In the northern Indian Ocean, they're called severe cyclonic storms. In the southwestern Indian Ocean, they're just called tropical cyclones.

To be classified as a hurricane, typhoon, or cyclone, a storm must reach wind speeds of at least 74 miles an hour.

If a hurricane’s winds reach speeds of 111 miles an hour, it is upgraded to an “intense hurricane.”

If a typhoon hits 150 miles an hour—as Usagi did in 2013—then it becomes a “supertyphoon.”

While the Atlantic hurricane season runs from June 1 through November 30, the typhoon and cyclone seasons follow slightly different patterns.

In the northeastern Pacific, the official season runs from May 15 to November 30. In the northwestern Pacific, typhoons are most common from late June through December. And the northern Indian Ocean sees cyclones from April to December.

For Hungry Minds

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Why the 2024 hurricane season could be especially active

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How Do Hurricanes Form?

Hurricane Fran. Image made from GOES satellite data.

Hurricanes are the most violent storms on Earth. People call these storms by other names, such as typhoons or cyclones, depending on where they occur. The scientific term for all these storms is tropical cyclone . Only tropical cyclones that form over the Atlantic Ocean or eastern Pacific Ocean are called "hurricanes."

Whatever they are called, tropical cyclones all form the same way.

Tropical cyclones are like giant engines that use warm, moist air as fuel. That is why they form only over warm ocean waters near the equator. The warm, moist air over the ocean rises upward from near the surface. Because this air moves up and away from the surface, there is less air left near the surface. Another way to say the same thing is that the warm air rises, causing an area of lower air pressure below.

A cumulonimbus cloud. A tropical cyclone has so many of these, they form huge, circular bands.

Air from surrounding areas with higher air pressure pushes in to the low pressure area. Then that "new" air becomes warm and moist and rises, too. As the warm air continues to rise, the surrounding air swirls in to take its place. As the warmed, moist air rises and cools off, the water in the air forms clouds. The whole system of clouds and wind spins and grows, fed by the ocean's heat and water evaporating from the surface.

Storms that form north of the equator spin counterclockwise. Storms south of the equator spin clockwise. This difference is because of Earth's rotation on its axis.

As the storm system rotates faster and faster, an eye forms in the center. It is very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye.

If you could slice into a tropical cyclone, it would look something like this. The small red arrows show warm, moist air rising from the ocean's surface, and forming clouds in bands around the eye. The blue arrows show how cool, dry air sinks in the eye and between the bands of clouds. The large red arrows show the rotation of the rising bands of clouds.

When the winds in the rotating storm reach 39 mph, the storm is called a "tropical storm." And when the wind speeds reach 74 mph, the storm is officially a "tropical cyclone," or hurricane.

Tropical cyclones usually weaken when they hit land, because they are no longer being "fed" by the energy from the warm ocean waters. However, they often move far inland, dumping many inches of rain and causing lots of wind damage before they die out completely.

Tropical cyclone categories:

The two GOES satellites keep their eyes on hurricanes from far above Earth's surface—22,300 miles above, to be exact! ( Learn more about this kind of orbit. )

These satellites, built by NASA and operated by the National Oceanic and Atmospheric Administration (NOAA), save lives by helping weather forecasters predict and warn people where and when these severe storms will hit land.

Related Resources for Educators

Our World: What is a Hurricane? Real World: Hurricane Hunters NASA's Eyes on Extreme Weather

Hurricane Katrina from space

Here is a movie of Hurricane Katrina, which struck the coast of Louisiana, Alabama and Mississippi on August 29, 2005, as a Category 3. This movie was made from images taken by the GOES weather satellite. In the movie you can see the storm starting to form in the Atlantic on August 24 and becoming more and more organized as it moves over the warm waters of the Gulf of Mexico.

If you liked this, you may like:

Smithsonian Ocean

Hurricanes, Typhoons, and Cyclones

Introduction, how hurricanes, form, move, and die, studying hurricanes, hurricanes and the natural world, humans and hurricanes, hurricanes and climate change, additional resources.

What’s the difference between a hurricane, a typhoon and a cyclone? The short answer is that there is none. They are all organized storm systems that form over warm ocean waters, rotate around areas of low pressure, and have wind speeds of at least 74 mph (119 km per hour). The reason for the three names is that these storms are called different things in different places. Scientists often use “tropical cyclone” as a generic term, while “hurricane,” “typhoon,” and “cyclone” are regional terms. In this article, “hurricane” will be used as an umbrella term to refer to them no matter where they are.

Hurricanes also get their own individual names , just like new babies. In the Atlantic, this practice began during World War II, when military meteorologists had to figure out how ships and planes could navigate around hurricanes. They initially tried several naming strategies, including naming hurricanes after the girlfriends of those observing them, but by 1953, meteorologists had begun using alphabetically ordered female names. In 1979, male names were added. Today, the World Meteorological Organization maintains six lists of alphabetically ordered male and female names that are rotated, meaning that eventually, each hurricane name will come around again—except if the hurricane is devastating enough that its name is retired (as were the names Camille and Katrina). Greek letters are used if the entire list is used within a season and if a hurricane forms outside the official hurricane season, it is named after the date on which it occurs. Unfortunately, if you want a hurricane to be named after you, you’re out of luck—there’s no procedure for that.

Whatever they’re named, hurricanes all form over tropical ocean waters, which are the source of their strength.  But people pay the most attention to them when they come near land, and rightly so, because hurricanes can do a lot of damage.  That’s because they release an enormous amount of energy—when fully developed, one hurricane can release heat energy equivalent to a 10-megaton nuclear bomb exploding every 20 minutes. They are also much bigger than other violent storms, like tornadoes. But at the same time, they are part of an enormous and complicated natural system that makes our planet a place we can live. They help keep the Earth’s temperature stable by moving heat energy from the equator to the poles. The more we know about hurricanes, the better we’ll understand how to prepare for them, so we can minimize damage and loss of life in the future.

Anatomy of a Hurricane

Hurricanes are more complicated than they appear on the radar image of a weather report. Air rushes around as if on a carousel, while at the same time moving inwards at the bottom of the storm and outwards at the top. Hot, wet air is constantly rising, and cool, dry air is constantly sinking. All the while, the entire system is moving across the surface of the Earth. Scientists who study hurricanes use esoteric terminology to describe the way they move them, speaking of things like deep moist convection, inertia-gravity waves, and vorticity. But, broadly speaking, a hurricane has only four main parts: the eye, the eyewall, the rainbands, and the cloud cover.

The eye of a hurricane is the cloud-free, relatively calm area right at the center of the storm, usually between 20 and 40 miles (32 to 65 km) in diameter. The eye remains calm and clear because air slowly sinks into it, suppressing the formation of clouds and keeping wind speeds below about 15 mph. It is surrounded by the eyewall, a towering ring of clouds characterized by heavy rain and strong winds. Wind speeds are fastest in the eyewall, which is why it is dangerous to assume a hurricane has died down as its eye moves over you. Super-strong winds will return as the hurricane continues to advance.

Surrounding the eyewall are bands of cumulus clouds, which are often tens of miles wide and usually release rain. These are the rainbands of the hurricane. Unlike the central ring of the eyewall, the rainbands spiral out from the center of the storm, sometimes intersecting the eyewall at their inner end. Outer rainbands may organize into a ring shape and move inward, replacing the original eyewall in a process that temporarily weakens the hurricane. Rainbands also produce tornadoes.

Finally, the rainbands and eyewall of a hurricane are overlaid with a dense cloud cover that makes the top of the hurricane appear smooth and continuous in satellite photographs. In fact, underneath the cloud cover, stormy rainbands (which you can see on radar images) alternate with rainless gaps where light breezes blow. Air that rises in the rainbands then spirals out of the top of the hurricane through this uppermost cloud layer.

How a Hurricane Dies

Hurricanes dissipate for a variety of reasons. They weaken quickly over land, which cuts them off from the moisture and heat of tropical ocean water and slows them down with greater friction than the sea surface. Even the warmest and swampiest areas of land, like the Everglades in Florida, will considerably slow down wind speeds and raise the pressure in the low-pressure center of a hurricane.  Vertical wind shear allows dry air into the core of a hurricane, which will weaken it considerably. Hurricanes also weaken when they move over colder water outside of the tropics. But none of these things are guaranteed to stop a hurricane. For instance, a hurricane might weaken when it passes over land, but rejuvenate when it moves out over tropical water again, like Hurricane Andrew did after passing over the Bahamas in 1992. 

If it moves out of the tropics, a hurricane can become a different kind of storm. If you live in the area roughly between 30 and 60 degrees latitude, you have probably experienced many mid-latitude cyclones—huge low-pressure systems, like nor'easters , that form when a cold front collides with a warm front and dump rain or snow over large areas for many days. Sometimes, a hurricane—a.k.a. a tropical cyclone—will exit the tropics and turn into a mid-latitude cyclone . When it does, the process is called an “extratropical transition.” These occur almost everywhere that tropical cyclones do, but they are particularly common in the West Pacific as well as in the North Atlantic Ocean, where almost half of hurricanes become mid-latitude cyclones (Extratropical transition almost never occurs in the North Indian ocean).

What happens during an extratropical transition? As it moves out of the tropics, a storm may encounter increased vertical wind shear, changes in humidity over distance, and decreased or quickly changing sea surface temperatures—all conditions that disrupt hurricanes. Instead of rotating symmetrically around a core, the storm disarranges itself and spreads out to a much larger size. The high-level canopy layer of clouds, which is characteristic of a hurricane, no longer resembles a symmetrical pinwheel in satellite images. The structure of the storm starts to look like it does when a warm and a cold front meet each other—a comma shape instead of a spiral shape. As it enters the mid-latitudes, the storm gets caught in the prevailing westerly winds, and it picks up speed, accelerating from perhaps 11 miles per hour in the tropics to 45 miles per hour at higher latitudes.

After the extratropical transition, a storm can still generate lots of rainfall and large ocean waves, and sometimes even hurricane-force winds.  Colloquially, we tend to keep calling a storm a “hurricane” even after it makes the transition. “Hurricane” Agnes was extratropical, for example, when it hit the Chesapeake Bay in 1972. A mid-latitude cyclone can be just as dangerous as a hurricane under certain circumstances, even though its winds are not as fast. But it too will eventually lose steam.

Could humans stop a hurricane? Certainly, humans are capable of changing the natural world in many ways, from damming mighty rivers to breaking shipping passages through Arctic ice. People have wondered if humans could stop a hurricane by seeding it with silver iodide, placing substances on the ocean surface to inhibit the ocean-air heat transfer, cooling surface waters with ice, pumping cold water to the surface from lower down in the ocean, adding moisture-absorbing substances to the hurricane, and even attacking it with nuclear weapons.  Seeding hurricanes with silver iodide was tried without demonstrable success in the US’s Project Stormfury . The other ideas are also impractical. Although some have a sound theoretical basis, hurricanes are so big and powerful that trying to stop them is more trouble than it’s worth. We can instead opt to spend resources on predicting them and building infrastructure to resist them.

Variation Across the Globe

The World Meteorological Organization designates seven different hurricane formation basins in the world.

We’ve already mentioned that a hurricane may be called any of several things depending on where it occurs. Hurricane-level storms that occur in the northern Atlantic Ocean and northeast Pacific Ocean are called hurricanes, while those in the Northwest Pacific are called typhoons. Hurricanes may hit the Caribbean, the Gulf of Mexico, and/or the east coast of the United States—and also can occur in the Northeast Pacific Ocean. Typhoons occur in the Northwest Pacific and may hit Vietnam, the east coast of China, and/or Japan, among many other locations. So if one term or the other sounds more familiar to you, it’s probably because of where you live. In other parts of the world, these storms are called severe tropical cyclones, severe cyclonic storms, and tropical cyclones. This can get confusing, but the key similarity is that they all gain their power from tropical warmth. In the South Pacific Ocean, for instance, it’s a hurricane if it occurs east of 160 degrees E and a severe tropical cyclone if it occurs west of 160 degrees E. To avoid confusion, most scientists use “tropical cyclone” as a general term (one which also includes tropical depressions and tropical storms) no matter where the storm occurs. Luckily, unless you’re a professional meteorologist, chances are you won’t have to worry about terminology – although it might serve you well to know the vocabulary when you’re listening to a dangerous weather report!

Calling hurricanes different things in different places is a matter of convention. However, there are substantive differences in the hurricane activity that occurs in different hurricane basins. For one thing, hurricane season varies from basin to basin. In the Atlantic basin, as we’ve mentioned, hurricane season lasts from June to November with a peak in September. By contrast, the Northwest Pacific basin sees hurricane activity all year round, although the main season is similar to the Atlantic’s. And, notably, the North Indian season has two peaks—one in May and one in November. The dip in hurricane activity between them is due to the way the monsoon affects wind shear.

Basins also differ in the number of hurricanes they see every year. In the Atlantic basin, the annual average is about six hurricanes. The Northwest Pacific sees by far the largest number of hurricanes each year, with an average of 16.5, while the North Indian Ocean sees the least, with an average of 1.5. More hurricanes occur in the Northern Hemisphere (69 percent) than the Southern (31 percent). Furthermore, of the hurricanes occurring in the Northern Hemisphere, 57 percent occur in the Pacific Ocean and 31 percent occur in the Indian Ocean, with only 12 percent occurring in the Atlantic.

While there are many different names for hurricanes across the globe, keep in mind that just because a storm swirls in a massive cyclone doesn't mean it is a hurricane from the tropics—there are other types of cyclones. Mid-latitude cyclones occur when a mass of cold air collides with a mass of warm air. An area of low-pressure forms where the two air masses meet and becomes the center point for the air to swirl around. While hurricanes often get national attention for their intensity, mid-latitude cyclones are the largest storms in the world, often covering an area two, three, or even four times the size of a hurricane.  Nor’easters , winter cyclones that form along the northeast coast of the United States, are one example of these mid-latitude cyclones that are driven by the significant temperature disparity between the cold air over land and the warm air over the Atlantic Ocean.

Hurricane Tracks

Knowledge of major atmospheric circulation patterns in different basins allows us to make generalizations about the most common tracks of hurricanes. For example, a hurricane that forms in the tropical Atlantic will typically be blown westward by the easterly trade winds that dominate the low latitudes. If it does not make landfall and instead dissipates in the Caribbean, or along the Gulf of Mexico coast, it will begin to move northward, “recurving” in a large counterclockwise motion around the area of high pressure surrounding Bermuda. As its latitude increases further, its path will bend northeast, steered by the prevailing westerly winds in the mid latitudes. (Source 3 p. 2312) If it never gets weakened by making landfall, the progressively colder waters as it moves poleward will eventually sap it of its strength, unless it undergoes extratropical transition. If you look at the aggregate of the paths of all Atlantic hurricanes over the past century or so, they will show you a broad-brush version of this recurvature.

General hurricane tracks can similarly be sketched for other hurricane basins, largely based on major atmospheric circulation patterns. For example, hurricanes in the Northwest Pacific basin tend to move westward towards the East China Sea and then recurve northward and northeastward around the area of high pressure in the Northern Pacific Ocean. Those in the Southwest Indian basin tend to proceed more directly westward across the Indian Ocean towards Madagascar and the eastern coast of continental Africa.

But hurricanes don’t always behave the way we expect them to. In 1938, for example, a hurricane spotted off the coast of Florida was later reported to be moving north and northeast, seemingly following the typical Atlantic recurvature and remaining out at sea. But the next day, the hurricane hit Long Island, New York, bringing with it a 20-foot wall of water called a storm surge and killing hundreds of people. The story of this hurricane, which was nicknamed the “Long Island Express,” illustrates why it’s so important that we devote resources and attention to predicting hurricanes—all the more because they can be so difficult to predict. We’ve come a long way since the Long Island Express, but we can continue to make our forecasts better.

The Hurricane Forecast

Over the past thirty years, we have gotten dramatically better at predicting the tracks of hurricanes—what paths they will follow and where they will hit land. In the late 1980s, the U.S. National Hurricane Center (NHC) misjudged a hurricane’s landfall location by an average of 350 miles when they made the prediction three days in advance. Nowadays, the NHC only misses by about 100 miles.  Moreover, although our ability to predict a hurricane’s track has vastly improved, we still struggle to predict its intensity, notably the speed (and consequent destructive potential) of its winds. Interestingly, knowing the literal size of a hurricane isn’t useful for an intensity prediction, although knowing the shape is. Except for sending pilots to fly through a hurricane and measure wind speed, using an algorithm called the Dvorak technique to interpret satellite images of hurricane shape is currently the best way to judge its intensity.

We’re still working on answering the two most important questions about hurricanes: will it hit me? and how bad will it be?

Missing by 100 miles is definitely better than missing by 350 miles, but it may sound like it’s still not that good. For instance, when Hurricane Irma hit Florida in 2017, it made a big difference to the people living there whether the landfall was predicted for the west coast of the peninsula or the east coast of the peninsula. Why aren’t we better at predicting hurricanes? The answer lies in a subdiscipline of mathematics called chaos theory that was developed during the 1960s by a meteorologist named Edward Lorenz. It tells us that a very small variation in initial conditions can produce a huge and sometimes unexpected variation in eventual outcomes. Lorenz called this the butterfly effect—imagine a butterfly in Brazil stirring up a tiny amount of air by flapping its wings, influencing a tornado in Texas several weeks later. The atmosphere is such a huge, multifarious, complicated system, with so many conditions that constantly change and are tough to measure accurately, that past a certain degree of accuracy, it is inherently impossible to predict. 

Of course, we do our best. Today, meteorologists use a range of models as well as their own savvy to make the very best predictions they can. Statistical models aggregate decades of historical data to predict what a hurricane is likely to do based on how past hurricanes have behaved. Dynamical models use powerful computers to model the atmosphere using equations and data from satellites, on-the-ground measurements, and hurricane flyers.  Meteorologists use their expertise to sort through all the data from the field and results from the models, and then they make a prediction . One of the ways hurricane forecasts have dramatically improved in recent decades is that they now more clearly communicate what meteorologists don’t know. The NHC used to draw a single line to indicate a hurricane’s predicted track. Now they map their prediction using a “cone of uncertainty”—an area encompassing a storm’s probable tracks that gets wider and wider as it goes out into the future and predictions are less and less certain.

In addition to predicting where a hurricane will go scientists must also predict to what extent it will intensify, and this too is a tough job. In general, scientists use data about how warm the ocean is, how much moisture there is in the air, and how consistent the winds are throughout the layers of the atmosphere to determine how much a hurricane will build in intensity. But there are other, smaller processes like thunderstorm formation, rain formation, and ice formation that can affect that intensification process. These small “microprocesses” are less understood and add complexity when trying to predict whether a hurricane will intensify or not. Hurricane Michael of 2018, the third strongest storm to hit the continental United States, is a prime example of such intensification . The storm jumped from a Category 2 to a Category 5 in only 24 hours, an intensification that proved to be tough to predict. It is likely that the data recorded by NOAA during Michael’s rapid intensification will help scientists with predicting similar intensifications in the future.

Just as technological advances have helped shape our understanding of recent hurricanes, historical research has aided in the study of past hurricanes. Researchers from one such study combed through recently translated indigenous Hawaiian newspapers to find references to natural disasters, a process that revealed a reference to the notoriously devastating hurricane in 1871. By piecing together damage accounts from across the Hawaiian Islands the historians determined the trajectory and intensity of the hurricane. This study not only broadened the understanding of one specific hurricane but also uncovered an important clue about the relationship between climate trends and hurricanes. 

Many things can throw a wrench into hurricane track predictions. Perhaps the most interesting situation is when a hurricane moves through an area containing another hurricane. First described by Japanese meteorologist Fujiwhara Sakuhei in 1921, the Fujiwhara effect occurs when two hurricanes get within 870 miles (1400 km) of each other. Once they are within that distance, they will rotate around a point directly between their centers, like dancers circling each other. If the storms are about the same size, the interaction might simply alter their trajectories before they break apart. On the other hand, if one storm is much smaller than the other, then the larger storm might absorb the smaller one once they get close enough. This happened in 2005 when Hurricane Wilma consumed Tropical Storm Alpha, as well in 1995 when Hurricane Iris absorbed Tropical Storm Karen. Even in a busy hurricane season, Fujiwhara interactions are actually relatively rare, but they can seriously complicate hurricane track predictions whenever there’s a chance they might occur.

How are Hurricanes Categorized?

Meteorologists classify tropical cyclones depending on their wind speed. If the storm’s fastest sustained winds are less than 38 miles per hour (61 km per hour), it is called a “tropical depression.” It doesn’t get the title “tropical storm” until its maximum sustained wind speed is greater than 38 miles per hour. Once the winds reach 74 mph (119 km per hour), the storm graduates to hurricane status. Usually, that is the wind speed necessary for an eye to form in its center. But the work of classification doesn’t stop there.

Meteorologists sort hurricanes into five categories depending on their maximum sustained wind speed. Ranging from the least severe “Category 1” to the most severe “Category 5,” these categories constitute the Saffir-Simpson Hurricane Wind Scale, which estimates the damage each kind of hurricane might cause if it were to make landfall. The Saffir-Simpson Scale was first developed in 1973 by Herbert Saffir, a construction engineer, and Robert Simpson, the director of the U.S. National Hurricane Center. Versions of the Saffir-Simpson Scale are used officially in the U.S., Japan, and Australia. Hurricanes of Category 3 or greater are called “major hurricanes” in the U.S. Typhoons with wind speeds of 150 miles per hour or greater—often Category 5 storms on the Saffir-Simpson Scale—are called “super typhoons.” High-level storms are frightening, but it is worth remembering that only a fraction of the total number of hurricanes per season actually make landfall. Terrifying Category 5 storms have petered out at sea without doing any human damage at all.

When we think of hurricane damage, we tend to think of the way these storms impact people and human infrastructure—and for good reason. But even when hurricanes barely touch humans, they can wreak havoc on the natural world .

A hurricane can leave its mark by rearranging geography. Hurricanes change coastlines, uprooting trees with their powerful winds and moving earth with the force of water. When Hurricane Agnes hit the Chesapeake Bay in 1972, it reconfigured the hydrology of the area, eroding away the mouths of tributaries to the Bay and transporting huge amounts of sediment upstream. In the tropics, new islands can be formed by the accumulation of coral skeletons, and sometimes entire blocks of reef are displaced by the hurricane and deposited on top of the shallow near-shore zone of the reef.

What’s more, a hurricane is usually bad news for local aquatic species and the oceanic ecosystems it encounters along its track. When Hurricane Agnes hit the Chesapeake Bay, it decimated the population of oysters and soft-shelled clams in that estuarine ecosystem. The culprit in this case wasn’t brute-force mechanical damage, but high water temperature and lots of rain. (Source 26 p. 18) By dumping a large amount of freshwater, a hurricane can induce a major change in the salinity of a saltwater or brackish ecosystem, which is very dangerous for species that aren’t built to tolerate freshwater. In the Chesapeake Bay, Agnes severely stressed organisms that lived only in a specific salinity range and lacked the ability to move into a less affected area. Hurricanes may also destroy coastal wetlands (Source 51), reduce the population of submerged aquatic plants—which shelter and feed many aquatic species—and depress the reproduction of fish whose eggs and larvae are washed away.

Coral reefs are particularly prone to hurricane damage because they are shallow-water ecosystems in the tropics. The damage begins with brute-force destruction dealt by high-intensity waves and debris in the water. Hurricanes smash and sweep away corals, and reefs that run perpendicular to the prevailing winds and waves bear the brunt of the impact. Passing near Rendezvous Caye, Belize, in 1961, Hurricane Hattie hit a barrier reef head-on. When the storm cleared, 80 percent of the corals from that reef had disappeared entirely. The most vulnerable coral species are those with long-delicate branches, one notable example in the Atlantic being the endangered staghorn coral, Acropora cervicornis. In enclosed bays with limited circulation, lowered salinity can kill the corals or stress them by causing them to expel the photosynthetic algae (zooxanthellae) that feed them . 

The results of a hurricane impact on a reef can be wide-ranging and long-lasting. When Hurricane Allen hit Jamaican reefs in 1980, it destroyed, overturned and fragmented corals. But for the fragile Acropora cervicornis , the deaths continued.  Five months after the storm, the species was 100 times less abundant than it had been immediately after the storm because of predation by snails, urchins, and damselfish on the survivors. Instead of reviving, the staghorn coral population collapsed. In the Caribbean overall, coral populations have a lot of trouble bouncing back after hurricanes, particularly when the ecosystem is already suffering from other human impacts like over-fishing and pollution. Following the year of impact, the rate of coral cover decline is 6 percent a year—higher than the normal decline rate of corals. Because corals play a foundational role in the reef ecosystem, their disappearance can make life much harder for other organisms that feed on them or use them for shelter.

When hurricanes make landfall, they damage land ecosystems too. In a tropical rainforest, a hurricane can uproot trees, snap their trunks, or denude them of leaves, as was the case in Puerto Rico after Hurricane Hugo in 1989 and Hurricane Maria in 2017. Because trees, like corals, are foundational to the ecosystem in which they live, dead trees can be bad news. Lucky for land-dwellers, trees are resilient—even some of those snapped by Hugo were found to be alive over a year later—and they’re less vulnerable to hurricane impact than ocean life, especially in forests farther inland. Still, an impact does alter a forest, notably by clearing space for grasses and faster-sprouting trees. No place emerges from a hurricane completely unscathed.

We give them human names, but hurricanes are massive, powerful weather phenomena. Although awe-inspiring, they are all too often tragic when they come ashore. When tragedy strikes, the impact, of course, depends on characteristics of the hurricane itself, which we can’t control. But the deadliest storms are not always those that are strongest at landfall. Much depends on us humans: how far in advance we knew the hurricane was coming, how effective our emergency procedures are, and how we have shaped the places that the hurricane hits. 

Direct Damage

Hurricanes kill far fewer people today than they did in the past. When the Galveston Hurricane hit Texas in 1800, it claimed 8,000 lives. The Galveston Hurricane has the highest death toll of any hurricane in U.S. history not because it was stronger than any of the hurricanes we see now, but because it occurred during an era when people were less capable of predicting and weathering hurricanes than they are today. In comparison, Hurricane Katrina in 2005, one of the worst natural disasters in the U.S. in recent years, claimed 1,800 lives. Elsewhere in the world, improvements in emergency procedure and infrastructure are still needed to reduce death tolls, but we’re on our way there. That’s the good news. The bad news is that we are still very vulnerable to hurricanes .

Hurricanes are among the deadliest of natural disasters. In Southeast Asia, Pacific hurricanes killed 740 people a year on average between 1990 and 1998. In the U.S., which is less vulnerable for several reasons (including a less active Atlantic basin) the annual average death toll was 50 for the years between 1963 and 2012. Note, however, that averages conceal enormous variability. A single hurricane, the Great Bhola Cyclone, killed almost half a million people when it struck Bangladesh in 1970. When Hurricane Katrina hit the US in 2005, it accounted for more than 40 percent of the hurricane-related deaths in the entire 50-year period. Overall, about one percent of the storms that hit the U.S. between 1963 and 2012 accounted for two-thirds of all the fatalities.

Hurricanes kill in multiple different ways. Wind is interestingly responsible for only eight percent of storm-related deaths, at least in the U.S. Water, on the other hand, has historically caused 90 percent of deaths, most of which (49 percent of the total) are specifically attributable to the phenomenon known as “storm surge.” As a hurricane churns across the ocean, its winds blow strongly enough to fill the air with sea spray and push the water into a wall in front of the storm. This wall of water piles higher and higher as the storm enters the shallow water near the shore, and by the time the hurricane hits, it may flood the land with anywhere from four to more than 18 feet of water. Damage depends on the timing of landfall—particularly if a hurricane hits during high tide—and the topography of the coast. The greater the area of shallow water approaching the coast, the larger the storm surge .  If the tide is high when the hurricane hits, that also boosts the water level. At its high point in the town of Waveland, Mississippi, Hurricane Katrina’s storm surge was 40 feet.

For Katrina, during which levee failures exacerbated the danger of the storm surge, as well as for other deadly U.S. storms like Betsy in 1965 and Sandy in 2012, storm surge was the primary cause of death. Unfortunately, that doesn’t mean we can concern ourselves only with storm surge because every individual hurricane is different and poses a different hierarchy of dangers. For instance, Hurricane Camille in 1969 and Hurricane Agnes in 1972 claimed most lives through rainfall-induced floods and mudslides, which are also a serious danger in Japan. Meanwhile, 20 of the 72 deaths caused by Hurricane Sandy were wind-related, resulting from falling trees.

Besides inflicting loss of life, hurricanes also cause loss of livelihood for those in their paths, by destroying communities and damaging property. On average, hurricane damages cost the U.S. 5.2 billion dollars every year between 1990 and 1998. In Southeast Asia, the annual cost averaged 3.1 billion dollars for the same period. Again, most of the damage is usually concentrated in a few especially devastating storms. Hurricane Katrina cost 108 billion dollars in damages, destroyed 68,729 homes, and deprived 3 million people of electricity.

Across the entire world since the year 1900, tropical cyclones have incurred the loss of more than 874,000 human lives and more than 179 billion dollars in property damage. Most of that cost comes immediately upon impact. But the total cost of a hurricane can’t be calculated a day or even a year after it hits. We often pay less attention to the indirect effects of hurricanes, especially since they’re less likely to make the news. But even when the indirect impact is less dramatic than the initial death and destruction, it’s certainly no less serious.

After the Fact

Hurricanes destabilize lives. The survivors of a hurricane might have lost loved ones or have no home to go back to. They may be newly deprived of the community relationships and support structures—not to mention the resources—they need to get back on their feet. Homelessness and displacement, food shortages, and lack of access to health care can make recovery a slow road. 

The aftermath of a hurricane often has consequences for public health. After Agnes in 1975, contaminated shellfish made people sick. More seriously, the aftermath of a hurricane often includes an outbreak of infectious and sometimes deadly disease, particularly in crowded areas with low immunization rates, limited access to clean water, and poor sanitation. When people must continue to stay in crowded and underserved shelters, epidemics can occur even months after the hurricane actually hits. For example, outbreaks of typhoid and the measles occurred five months after Hurricanes David and Fredrick hit the Dominican Republic in 1979. Floodwaters are also great places for bacteria to spread. A few weeks after Hurricane Harvey in 2017 a woman died of a flesh-eating bacteria that she contracted from the floodwaters after a fall. Luckily it was an isolated incident. But poor living conditions aren’t the only things that disaster responders have to keep track of. When Hurricane Flora hit Haiti in 1963, it gave mosquitoes new breeding grounds and forced the survivors outside where they could be bitten, contributing to more than 75,000 cases of malaria. A similar outbreak occurred soon after Hurricane Mitch hit the Caribbean in 1998. 

Along with physical ailments like injury and disease, hurricanes also leave invisible psychological and emotional damages in their wakes. It’s not surprising that living through a hurricane might make someone anxious or fearful of other disasters, or give them reason to grieve, and some survivors struggle with continuing psychological consequences, up to and including post-traumatic stress and depression. Part of the problem is in the timing. People generally do a good job of rushing in to support survivors right after the disaster strikes, but some psychological hurts make themselves known over time and once support ebbs, survivors may feel abandoned. After a hurricane, it’s important to keep an eye out for people whose mental health might be affected, particularly people who are stressed by recent bereavement or previous trauma. 

Preparedness and Response

There is no way for humans to stop a hurricane, and sometimes people foolishly ignore the risks, even when they are well publicized. But the earlier and more accurate forecasts are, the faster evacuation orders can go out, moving people out of harm’s way. Track and intensity predictions for Hurricane Katrina were accurate enough, for example, that evacuation could have been ordered two or three days in advance. Because the evacuation was well organized and roads were ready to accommodate the outflow, the evacuation saved many lives. Afterwards, however, supplies had trouble getting into the affected area, and people had trouble getting out of it, exacerbating the death toll. Carribean Islands, are a bit trickier to evacuate. In the aftermath of Maria in 2017, the entire island of Puerto Rico was devasted and the aid response was slow. A month after the hurricane many on the island were still without food, clean water, and power—circumstances that many call a humanitarian crisis. By contrast, after Hurricane Sandy hit New York in 2012, responders made food and water immediately available. After an impact, it is critical to have a well-organized and effective emergency response.

But well before the event, we need to pay attention to the other major player in a hurricane impact—the landscape that gets hit. Infrastructure can be designed with hurricanes in mind on a much larger scale than just boarding up windows before a storm hits (although that is an important precaution to take). Seawalls and artificial levees must be built strong and high enough to withstand storm surge. Power can be provided to towns and cities via microgrids , small-scale electric grids that are both self-contained, meaning they’re not connected to the regional power grid, and self-sufficient, meaning they have their own source of power such as a gas turbine or solar panels. When Hurricane Sandy hit New York City, New York University kept its students safe on a campus fueled by its very own microgrid. An entire city on microgrids would have a significantly reduced risk of widespread power outages during a hurricane.

As important as the infrastructure we install, however, could be the infrastructure that we don’t. Often, we’re better off leaving nature to erect its own barriers against hurricanes. Hurricane Katrina provides a case study. Between 1958 and 1968 a canal leading inland from the Gulf of Mexico was built. It was known as the Mississippi River Gulf Outlet, or MRGO, and nicknamed “the hurricane highway.” Experts believe that the canal system adjacent to New Orleans funneled floodwaters into the city during the storm. Moreover, MRGO, as well as other human infrastructure, replaced coastal wetlands on the Gulf Coast. In the half century prior to Hurricane Katrina, Louisiana lost 1,700 square miles of its wetlands to development. Similar patterns of wetland destruction occur in other hurricane-vulnerable locations across the globe, like Thailand.

Why do wetlands matter? Quite simply, they are the front line of protection against hurricanes. It’s far safer to have wetlands than hurricane-vulnerable infrastructure like a canal. Wetlands sponge up the energy of a hurricane from the moment it hits land. Because wetlands divvy up open water with natural levees and other obstacles like plants, they make it more difficult for the hurricane’s winds to whip up big waves. They also act like a strainer for the storm surge, decreasing its force and height. Each square mile of wetland, in fact, reduced the height of the storm surge by three inches when Hurricane Andrew hit Florida in 1992. Overall, each square mile of wetland loss corresponds to a loss of 8.55 million dollars in hurricane damages. These coastal ecosystems—ranging from marshes in Florida to mangrove forests in Thailand—may well be the best hurricane buffers we’ve got. In the ocean, coral reefs can play a similarly vital role in protecting against large waves. All we have to do is preserve these important natural barriers.

We know that climate can affect hurricane formation.  For example, when the climate phenomenon known as El Niño causes warmer-than-average water in the tropical Eastern Pacific, there is a corresponding decrease in Atlantic hurricane activity. Conversely, when the rainfall in the western Sahel region of sub-Saharan Africa increases, so does the number of especially intense Atlantic hurricanes. Scientists also recently discovered that hurricanes in the Atlantic intensify more rapidly now than when compared to 30 years ago. It is this 30 year time period that the Atlantic Multidecadal Oscillation , a cycle of Atlantic Ocean warming and cooling, was in its warm phase. This signals that human-caused climate change could also affect how hurricanes form and develop.

Strong Storms

Most scientists agree that as the climate gets hotter because of human emissions of carbon dioxide and other greenhouse gases, hurricanes will likely get stronger. In fact, the hike in temperature between the 1970s and now is about the same for hurricane formation areas as it is for the global average. We know that the relationship between water temperature and hurricane formation is complicated, but broadly speaking, hotter water means more energy is available to be released, and more energy means a more intense hurricane. Scientists have recently run an elaborate computer simulation to predict how hurricane activity will change as we approach the year 2100. They found, interestingly, that the overall number of tropical cyclones will decrease—but that the number of Category 4 and Category 5 hurricanes will double. Although this prediction might vary from study to study based on the specifications of the model scientists use, this is still bad news, especially because Category 4 and 5 hurricanes are by far the most destructive of storms. They accounted for 48 percent of hurricane damage in the U.S. during the last century, even though they only constituted 6 percent of the storms that made landfall. Another simulation study found that in the next few decades hurricanes will have faster winds, move slower , and be on average 24 percent wetter. A slow hurricane means that the lingering storm has more time to dump rain in one area and cause flooding, more time for winds to pummel buildings and trees, and more time to affect storm surges which overall, creates a more punishing storm.

Increased Frequency

There have in fact been more Category 4 and 5 hurricanes in recent decades, although scientists disagree about how much of this pattern is due to human-caused global warming. Some think it’s none. Hurricane activity naturally varies in response to a climate cycle called the Atlantic Multidecadal Oscillation, which might account for the recent increase in Category 4 and 5 hurricanes—or there might be a human-caused increase on top of the natural variation. Also, global warming’s effect on the intensity of hurricanes may have been partially canceled out by the opposing effect of a group of atmospheric pollutants known as aerosols. It’s very hard to disentangle causes without a lot of long-term data , and in addition, the connection between hurricanes and climate has not been studied as much outside of the Atlantic basin. So while there is no scientific doubt that hurricanes will get stronger as the climate warms, there is some uncertainty about the timing of these changes.

As we move forward, one interaction between hurricanes and climate change is easy to predict: storm surges will become more destructive with rising sea levels . When the water gets higher, there is a corresponding increase in the height of a hurricane’s storm surge. And some regions that are already vulnerable to hurricanes, like the Gulf of Mexico coast, will also experience particularly high sea level rise .  In the case of Hurricane Sandy, eight inches of sea level rise over the course of the last century put an additional 75,000 people and $8.9 billion worth of property at risk of damage when the storm hit. Hurricanes are already one of the most destructive phenomena we experience, and they could get much more destructive in the future unless we act to limit climate change.

NASA's Earth Observatory NASA Hurricanes and Typhoons National Hurricane Center National Geographic Hurricanes 101

News Articles: The Weatherman Is Not a Moron (The New York Times)

Books: Isaac’s Storm: A Man, A Time, and the Deadliest Hurricane in History by Erik Larson The Perfect Storm by Sebastian Junger

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What is a hurricane? Facts to know

The official Atlantic hurricane season begins June 1 and runs through Nov. 30, although hurricanes can form for a few weeks before and after that window. In other parts of the world, like the western Pacific, hurricanes can form year-round.

What is a hurricane?

"Hurricane" is the name used for the most powerful tropical cyclones in the Atlantic Ocean and the northeastern Pacific Ocean — those bearing sustained winds of 74 mph and above. Hurricanes are generally called "typhoons" in the northwestern Pacific Ocean and "severe cyclonic storms" in the south Pacific and the Indian Ocean.

Tropical cyclones are rotating low-pressure systems carrying thunderstorms but no identifiable "front," which is the boundary that separates two air masses of different densities in most storm systems.

Tropical cyclones with sustained winds of less than 39 mph are called "tropical depressions," while those with sustained winds of 39 mph to 73 mph are called "tropical storms."

What are the hurricane categories?

A hurricane's power is measured on the Saffir–Simpson Hurricane Wind Scale, which was developed in 1971 by Herbert Saffir, U.N. civil engineer who died in 2007, and Robert Simpson, then the director of the National Hurricane Center, who died in 2014.

The scale separates hurricanes into five categories, with 1 being the weakest and 5 being the strongest. Category 3, 4 and 5 hurricanes are called "major hurricanes."

• Category 1 (74 mph to 95 mph): Very dangerous winds with some damage to homes and trees.
• Category 2 (96 mph to 110 mph): Extremely dangerous winds causing extensive damage to homes, trees and roads, often resulting in near-total power loss for several days to weeks.
• Category 3 (111 mph to 129 mph): Devastating damage to homes, trees and roads. Electricity and water are often unavailable for several days to weeks.
• Category 4 (130 mph to 156 mph): Catastrophic damage to homes, trees and power infrastructure. Most areas are uninhabitable and without power for weeks or months.
• Category 5 (157 mph and higher): Most homes and other structures are destroyed. Most areas are uninhabitable and without power for weeks or months.

National Hurricane Center: About the Saffir-Simpson Hurricane Wind Scale (PDF)

How do hurricanes form?

Tropical cyclones develop when low-pressure systems gather heat and energy as they absorb warm ocean water near the equator. Evaporation from the ocean surface fuels them like giant heat engines, creating powerful winds twisting around a relatively peaceful center, called the "eye." (The winds rotate counterclockwise north of the equator and clockwise south of the equator.)

When a tropical cyclone makes landfall or crosses over cooler waters, its source of power disappears, so the storm begins to weaken.

How are hurricanes named?

Hurricanes and other tropical cyclones are given men's and women's names by the World Meteorological Organization to make them easier to keep straight.

Different lists of names are used for different regions, reflecting local naming customs (the letters Q, U, X, Y and Z are never used for Atlantic hurricanes). When a tropical cyclone is particularly deadly or damaging, its name is retired.

As of January, 82 Atlantic hurricane names had been retired . The most in any year, five, blew through in 2005: Dennis, Katrina , Rita, Stan and Wilma.

National Hurricane Center: Tropical cyclone names through 2022

Which modern hurricanes have caused the most damage?

Reliable records have been kept only for the last half-century or so. Ranking hurricanes by the extent of the damage they cause is difficult, because monetary inflation and ever-improving building codes make comparisons imprecise.

Here's a list of the deadliest Atlantic hurricanes since 1900:

• Hurricane Mitch , Central America/Yucatán Peninsula/South Florida, October-November 1998 — 11,374 people killed
• Hurricane Fifi-Orlene , Jamaica/Central America/Mexico, September 1974 — 8,200 people killed
• Hurricane Flora , Caribbean/Florida, September-October 1963 — 7,193 people killed
• Unnamed hurricane ("Galveston" hurricane), Caribbean/Texas, August-September 1900 — 6,000 to 12,000 people killed
• Unnamed hurricane ("Okeechobee" hurricane), Lesser Antilles/Puerto Rico/Florida, September 1928 — 4,075 people killed

And here's a list of the deadliest tropical cyclones around the world since 1900:

• Great Bhola Cyclone , Bangladesh, November 1970 — 300,000 to 500,000 people killed
• Super Typhoon Nina , China, August 1975 — about 171,000 people killed
• Cyclone 02B , Bangladesh, May 1991 — 138,866 people killed
• Cyclone Nargis , Myanmar, May 2008 — 138,366 people killed
• Unnamed typhoon , Swatow (now Shantou), China, July 1922 — about 100,000 people killed

SOURCES : U.S. National Hurricane Center ; Hurricane Research Division, Atlantic Oceanographic & Meteorological Laboratory ; U.N. Office for Disaster Risk Reduction ; World Meteorological Organization ; Centre for Research on the Epidemiology of Disasters , Catholic University of Louvain, Brussels; DisasterHistory.org , University of Manchester, England

ENCYCLOPEDIC ENTRY

Storm surge.

A storm surge is a rise in sea level that occurs during tropical cyclones, intense storms also known as typhoons or hurricanes

Earth Science, Meteorology, Oceanography, Geography

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A storm surge is a rise in sea level that occurs during tropical cyclones , intense storms also known as typhoons or hurricanes . The storms produce strong winds that push the water into shore, which can lead to flooding . This makes storm surges very dangerous for coastal regions. Tropical cyclones are circular storms characterized by high winds and heavy rainfall. They form over warm, tropical oceans. The center of a cyclone is called the eye . The eye is surrounded by a ring of clouds called the eye wall , where the winds are strongest. Surrounding the eye wall are clouds that spiral outward, called spiraling rain bands. A storm surge is primarily caused by the relationship between the winds and the ocean’s surface. The water level rises where the winds are strongest. In addition, water is pushed in the direction the winds are blowing. The rotation of the Earth causes winds to move toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere —a phenomenon known as the Coriolis effect . If a cyclone develops in the Northern Hemisphere , the surge will be largest in the right-forward part of the storm . In the Southern Hemisphere , the surge will be largest in the left-forward part of the cyclone . Another factor contributing to storm surge is atmospheric pressure . Atmospheric pressure is the force exerted by the weight of air in the Earth’s atmosphere . The pressure is higher at the edges of a cyclone than it is at the center. This pushes down the water in the outer parts of the storm , causing the water to bulge at the eye and eye wall —where the winds have helped add to the rise in sea level . More factors contribute to the strength of a storm surge as the dome of water comes ashore. The water level can reach as high as 10 meters (33 feet) if the storm surge happens at the same time as high tide . The slope of the land just off the coast also plays a part: Water will more easily flood a shallow coast than a steep one. Storm Surges and Coastal Communities Tropical cyclones , and the storm surges they generate , are a serious hazard for coastal areas in tropical and subtropical regions of the world. Developing in the late summer months (July-August in the Northern Hemisphere , January-February in the Southern Hemisphere ), when the waters are warmest, tropical cyclones hit regions as far apart as the Gulf Coast of the United States, northwestern Australia and Bangladesh. When a cyclone hits land, the accompanying storm surge will most often flood the surrounding coastal area. Flooding is responsible for most deaths and economic damage associated with tropical cyclone landfalls. When a hurricane hit Galveston, Texas, in 1900, the storm surge was responsible for approximately 6,000 deaths. In East Pakistan (now Bangladesh), the Bhola cyclone killed as many as 500,000 people in 1970. The storm surge from the Bhola cyclone was estimated to be 10 meters (33 feet) high. Improvements in forecasting cyclones and issuing early warnings to the public have become indispensable as both coastal populations and the occurrence of extreme storms continue to rise.

However, even sophisticated meteorology and storm warnings do not always protect against devastating storm surges . Hurricane Katrina ’s storm surge flooded the U.S. coastal communities of Louisiana and Mississippi, as well as the urban areas of New Orleans, Louisiana, and Biloxi, Mississippi, in 2005. The flooding killed more than 1,500 people in New Orleans alone, and caused millions of dollars in damage. Homes, businesses, schools, and hospitals were destroyed. Still, improvements in forecasting greatly benefit regions like the Chesapeake Bay , in the U.S. states of Maryland and Virginia. The Chesapeake Bay suffered severe damage from Hurricane Isabel in 2003. Emergency managers failed to predict Isabel’s extreme storm surges , which caused widespread flooding in the region. Now, meteorologists and emergency managers monitor the storms forming in the southeast more closely. New computer simulations by the Federal Emergency Management Agency (FEMA) examined the effects of a Category 4 hurricane (131-155 mph winds ) landing in the U.S. states of North or South Carolina, hundreds of miles south of the Chesapeake. The simulation showed the hurricane could produce storm surges as high as 5 or 6 meters (18 or 20 feet) along the Chesapeake shoreline . FEMA used the latest version of its computerized SLOSH model to predict the surge. An acronym for "Sea, Lake, and Overland Surges from Hurricanes ,'' the SLOSH program is used by the National Weather Service and the National Hurricane Center. The Maryland Emergency Management Agency is now working with the U.S. Army Corps of Engineers and local officials to turn the SLOSH simulation data into updated maps for emergency planning. The new maps show how far inland flooding could stretch under certain conditions. With this new forecasting data , emergency planners and citizens will be better prepared for storm surges . Government agencies can arrange for residents to evacuate . Some residents don’t have cars and may require transportation to safer ground. Others may not have a place to go and require emergency shelter. Many residents, such as those in hospitals and prisons, are especially at risk. Advance warning of a strong storm surge also allows homes and businesses to prepare for damage. Business owners can relocate expensive machinery or tools to safe areas, and homeowners can board up windows to protect against strong floods or move furniture and other valuables to a second story. Wetlands Coastal residents can reduce the damage done by a storm surge by protecting local wetlands . Wetlands , such as swamps , estuaries, and mud flats , act as sponges for tropical cyclones . As the cyclone makes landfall, the marshy land and plants absorb the water and the energy of the storm surge . Silt and swamp vegetation prevent the most intense part of the storm surge from hitting homes and businesses. Estuaries are such an important part of our natural environment that the U.S. Environmental Protection Agency (EPA) created the National Estuary Program in 1987. This program seeks to improve the quality of estuaries to protect important wildlife habitats , public water supplies, and coastal regions affected by severe storms . The development of coastal wetlands for housing, industry, or agriculture reduces the natural barrier that wetlands provide. Communities can protect themselves against storm surges by maintaining healthy coastal wetland ecosystems .

The Saffir-Simpson Scale Just before the 2010 hurricane season, scientists removed storm surge from the Saffir-Simpson Hurricane Wind Scale, a five-category system that describes the strength of the storms. The problem, scientists said, is that the size of a storm surge doesn't always match up with the strength of a hurricane. It was the first change to the scale in about a decade. Storm surge forecasts will still be part of hurricane advisories.

Different Names, Same Storm Hurricanes and typhoons are the same as cycloneswhich name is used depends on what part of the world the storm is in. The storms are called hurricanes in the North Atlantic Ocean, the Northeast Pacific Ocean, or the South Pacific Ocean. They are called typhoons in the Northwest Pacific Ocean.

Storm Tide If a cyclone makes landfall while the tide is rising, the tide and the cyclone can create an especially high storm surge. This is sometimes referred to as a "storm tide."

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Related Resources

• What is a Hurricane?

A hurricane is a large, swirling tropical storm that forms in the open ocean and moves towards land at speeds of over 72 miles per hour. Hurricanes form over the Northeast Pacific or the North Atlantic Ocean. They are known as cyclones in the Indian Ocean and South Pacific, and typhoons when they form in the Northwest Pacific.

How Are Hurricanes Formed?

Hurricanes begin forming as tropical disturbances in areas of the ocean that are warmer with temperatures of at least 80 °F. These disturbances are because of low pressure caused by the warm seas. If the ocean temperature continues rising, a storm forms. The speed of the storm may vary, but when it reaches 38 miles, it becomes a tropical depression. The tropical depression gradually develops into a tropical storm and acquires a name when it reaches wind speeds of 39 miles. When the storm sustains wind speeds of 74 miles/h, it is declared a hurricane. Hurricanes produce a staggering amount of energy by absorbing the moist and warm ocean air and releasing it through condensation during thunderstorms. Hurricanes revolve around a calm low-pressure center (eye) that can be 20- to 30-mile wide. The spinning part of the hurricane is known as the “eyewall,” and it is responsible for the strong winds and rain.

Damaging Effects of Hurricanes

When a hurricane reaches land, it causes damages that can be catastrophic and results in a storm surge that can rise to 20 feet and extend for about 100 miles. In fact, storm surges result in 90% of the deaths caused by hurricanes. The winds not only cause massive damage but can also spawn tornadoes. Excessive rainfall cause floods that may occur miles inland. The best way to defend against a hurricane is to get out of its way; most of the hurricanes are forecasted and warnings issued to the communities that may be affected 24 hours prior to the hurricane.

Classification of Hurricanes

The Saffir–Simpson hurricane wind scale is used to classify hurricanes. The scale measures the wind-speeds to determine the intensity of the hurricane. There are five levels of the scale known as categories.

Category 1: Winds 74-95 mph (119-153 km/hr.)

Category 2: Winds 96-110 mph (154-177 km/hr.)

Category 3: Winds 111-129 mph (178-208 km/hr.)

Category 4: Winds 130-156 mph (209-251 km/hr.)

Category 5: Winds more than 157 mph (252 km/hr.)

Naming of Hurricanes

Hurricanes are named because several can occur at the same time. Names make it easier to track and ensure that people are talking about the same thing. A storm is named after it graduates to a tropical storm and the name sticks if it develops into a hurricane. Before the early 1950s, hurricanes were named by the year and the order they occurred within the year. Metrologists realized that shorter names were much easier to remember and reduce confusion when citing a hurricane and the use of female names was adopted in the US. By 1978, the Northern Pacific storms were named using both male and female names.

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Stormy Daniels Takes the Stand

The porn star testified for eight hours at donald trump’s hush-money trial. this is how it went..

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This episode contains descriptions of an alleged sexual liaison.

What happened when Stormy Daniels took the stand for eight hours in the first criminal trial of former President Donald J. Trump?

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On today’s episode

Jonah E. Bromwich , who covers criminal justice in New York for The New York Times.

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In a second day of cross-examination, Stormy Daniels resisted the implication she had tried to shake down Donald J. Trump by selling her story of a sexual liaison.

Here are six takeaways from Ms. Daniels’s earlier testimony.

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