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- Hurricane Facts
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- What Causes a Hurricane?
- Hurricanes and Climate Change
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Pounding rain, raging winds, and devastating storm surge. When hurricanes make landfall, they bring a trifecta of threats capable of leveling communities and destroying lives and livelihoods. Named after the ancient indigenous god Hurican (the Carib god of evil), hurricanes are giant energy powerhouses. Here’s a look at what they’re made of, how climate change is affecting them, and how to limit damage from their wrath.
What Is a Hurricane?
A hurricane is an intense low-pressure weather system of organized, swirling clouds and thunderstorms that gain energy from warm tropical waters. While we’re using the term hurricane here, these systems are actually identical to typhoons or cyclones—with the name depending on where they occur. They’re called hurricanes in the Atlantic and in the central and eastern Pacific, typhoons in the northwestern Pacific, and cyclones in the Indian Ocean and South Pacific (more on this later). To be classified as a hurricane, wind speeds must reach 74 miles per hour (mph). That’s powerful enough to peel off roof shingles.
With their distinctive buzz-saw shape when viewed from above, hurricanes spin around a low-pressure center known as the eye—an area of calm and sometimes even clear sky. Journalist Edward R. Murrow, who flew through the eye of 1954’s Hurricane Edna, described it as “a great amphitheater, round as a dollar . . . a great bowl of sunshine.” The eye, which is typically 20 to 40 miles across, is surrounded by a circular “eye wall,” a dense wall of clouds and thunderstorms containing the most violent wind and rain. Beyond the eye wall and extending for as much as hundreds of miles, slowly rotating rain bands bring their own intense thunderstorms, capable of producing fierce winds and tornadoes.
Meteorologists measure a hurricanes’ strength based on the intensity of their sustained wind speeds and rate them using the Saffir-Simpson Hurricane Wind Scale. There are five categories of hurricane: a category 1 produces sustained winds of at least 74 mph, a category 2 storm begins at 96 mph, and a category 3—considered “major”—has winds of at least 111 mph. Categories 4 and 5—both considered “catastrophic”—generate winds of at least 130 mph and 157 mph, respectively.
The category of a hurricane reflects only the wind speed, not the overall potential for damage. In fact, the greatest risk comes from flooding associated with the storm surge or the intense rains the storms generate. Consider Superstorm Sandy, which arrived in New Jersey with 80 mph winds (barely over the category 1 minimum) but still proved devastating. Sandy lacked the extreme winds of a major storm, but the massive swell of water it generated slammed into New Jersey and New York, obliterating beaches and boardwalks, filling subway tunnels, inundating neighborhoods, and destroying massive amounts of infrastructure. Similarly, most of the damage caused by hurricanes Harvey and Florence were largely attributable to torrential rains, not wind or even storm surge in coastal areas.
For the Atlantic basin (comprising the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico), hurricane season runs from June through November. The Atlantic season peaks between mid-August and late October and produces an average of 6.2 hurricanes a year—with more than a third of them typically measuring category 3 or above. Hurricane season in the eastern Pacific, an area extending from the U.S. West Coast to 140 degrees west longitude (about due south of Alaska’s eastern border), lasts from mid-May through November. An average of 8.5 hurricanes a year appear in the eastern Pacific, with fewer than half measuring category 3 or above. The central Pacific, which includes Hawaii, typically sees four to five hurricanes a year during its season—June through November—with most storms appearing in August and September.
Fewer than two hurricanes make landfall in the United States in a typical year, according to data from 1851 to 2017, with an average of three major hurricanes pummeling the coastline every five years. About 40 percent of hurricanes make landfall in Florida, while nearly 90 percent of major hurricanes hit either Florida or Texas. Hurricane Michael in October 2018 was the first category 4 storm to strike the Florida Panhandle since record-keeping began in 1851—and the strongest to make landfall the United States in more than 25 years.
How Is a Hurricane Different from Other Storms?
The fact that hurricane, typhoon, and cyclone are all used for the same weather phenomena can be confusing. This explains where (and when) they occur, and how they’re different from other major rain and wind events.
A typhoon is tropical cyclone that occurs in the northwestern Pacific basin, covering eastern and southeastern Asia and Micronesia. Nearly one-third of the world’s big storms develop here, with an average of 16.5 typhoons a year, mostly between May and November. The world’s largest recorded tropical cyclone was Super Typhoon Tip, which slammed into Japan in 1979, producing winds of 190 mph and measuring 1,380 miles in diameter, about the distance from New York City to Dallas.
A cyclone—or a “tropical cyclone” or “severe tropical cyclone”—occurs in the Indian Ocean and South Pacific and is the equivalent of a hurricane or typhoon elsewhere. Cyclones generally occur from May to November in the northern Indian Ocean and between November and April in the southern Indian Ocean and South Pacific. Areas impacted by cyclones include Southeast Asia, northern Australia, the South Pacific islands, India, Bangladesh, and some parts of East Africa, including Indian Ocean islands such as Mauritius and Madagascar.
Although both storms are known for their spiraling, violently destructive winds, the similarity between tornadoes and hurricanes ends there. A hurricane forms over tropical waters and can span several hundred miles, last for days to weeks, and be predicted well in advance. A tornado, on the other hand, forms over land as a tall, rotating column of air that extends from the base of a thunderstorm (including those produced by hurricanes) to the ground. The largest tornadoes are just over a quarter mile wide and typically last for no more than an hour, though they can pack a punch in terms of wind speed—as high as 300 mph. (Most hurricanes top out around 180 mph.) Advance warnings for tornadoes are typically less than 15 minutes.
Similar to a hurricane, a monsoon can produce torrential rains that lead to damaging floods, injury, and death. But while a hurricane is basically a single weather event, a monsoon is a seasonal change in the prevailing winds that move from ocean to land—and vice versa—and can produce months of wet (or even dry) conditions. Although most often associated with Southeast Asia, monsoon winds exist around the world, including the U.S. Southwest.
Hurricanes leave a trail of devastation in their wake, piling up costs in terms of lives and livelihood. Here are some of the ways these storms impact communities and the surrounding environment.
How Hurricanes Impact Communities
Hurricanes create a range of short- and long-term health and economic woes, with socially vulnerable populations often shouldering the greatest burden.
Flooding isn’t just the deadliest threat; it also causes tremendous damage to homes, buildings and infrastructure, whether from storm surge or flooding after extreme rains. In fact, flooding was the main cause of damage for many of the costliest hurricanes. The trend toward storms with heavier rainfall has put a strain on the National Flood Insurance Program (NFIP), which has been in debt since Katrina caused $16.3 billion in flood-related damages in 2005. More than 80 percent of the program’s payouts to cover losses have occurred since 2000, even though it was created in 1968.
Hurricanes are the costliest form of weather disaster, accounting for more than half of the total damages from billion-dollar U.S. weather events since 1980. Through September 2018, when Hurricane Florence battered the East Coast, 41 hurricanes each averaged nearly $22 billion in losses (the data do not include Hurricane Michael). That figure includes everything from wrecked homes and waterlogged hospitals to mangled material assets such as cars and boats. It also includes damage to public infrastructure such as roads, bridges, and power lines, along with lost wages and income-generating assets such as crops, livestock, and businesses. It does not include health-related costs or values related to lost lives.
Climate change is expected to further increase the tab, with potential future losses from hurricanes and other extreme weather events projected to as much as double by 2100.
Hurricane Maria, which struck Puerto Rico in 2017 and is considered the deadliest hurricane in recent U.S. history, shows how a storm can overwhelm the local electricity, water, and medical infrastructure and take a long-term toll on human health, including mental health.
The second-most deadly storm in recent years, Hurricane Katrina struck the U.S. Southeast in 2005 and claimed more than 1,800 lives. The majority of Katrina’s victims perished from the storm surge, which is the cause of about half of all U.S. fatalities related to a hurricane's force. Flooding from rainfall is the second-gravest danger, resulting in about a quarter of immediate deaths. While a storm’s strength is based largely on wind speed, deaths from falling debris and other wind-borne hazards—including tornadoes spawned by the hurricane—account for a little more than one-tenth of fatalities. Drownings, either near shore or out at sea, account for 12 percent.
These statistics don’t tell the full story of how a hurricane impacts health, however. Flood-induced sewage overflows from wastewater treatment plants can dump fecal bacteria into floodwaters and waterways, increasing the risk of skin, eye, ear, and gastrointestinal infections. Runoff from toxic waste sites and factory farms can expose nearby residents to hazardous waste. After the storm has passed, flooded, water-damaged homes can harbor bacteria and mold, making the air unhealthy to breathe. Mold can be a particularly pervasive health hazard, since it starts growing immediately and can be hard to detect and remove.
Who are the most vulnerable?
While hurricanes impact everyone living in a storm-affected area, those impacts aren’t shared equally. Low-income communities, people of color, and the elderly are disproportionately exposed to storms. These populations often live in suboptimal housing situated in areas particularly vulnerable to storm threats—sometimes close to polluting industries that raise the risk of contamination via pipeline or facility leaks or chemically contaminated floodwaters. Due to limited mobility, lack of funds, or insufficient storm-warning information, these communities often face greater challenges in escaping impending storms as well. Often they may be unable to bounce back as quickly after a hurricane has passed, facing challenges in accessing public disaster relief, job assistance, and affordable housing.
How Hurricanes Impact the Environment
Ravaged homes and submerged streets are the images most often seen on the news after a hurricane strikes, but coastal ecosystems—both on land and at sea—experience their own forms of devastation as well.
When seawater surges into wetlands, bays, and estuaries, the onslaught of salt can harm freshwater marsh grasses and plants as well as crabs, minnows, and other marine life. When saltwater washes over land, it can harm or even kill bottomland forests and coastal trees unaccustomed to the uptick in salinity. The opposite can happen, as well: Heavy rains can cause freshwater to flood into coastal basins, decreasing the salinity of typically brackish waters and imperiling the species that depend on them.
Dislocation of species
Both strong winds and the relative calm of a hurricane’s eye (which acts as a natural cage) can push birds, particularly seabirds and water fowl, hundreds of miles from home. Meanwhile, floodwaters—from both storm surge and overflowing rivers and streams—can strand animals far from their natural territory.
Hurricane-force winds can uproot trees and bushes or strip them of their leaves, seeds, fruit, berries, and branches, damaging entire wooded ecosystems. This can not only create short-term food shortages for species, but also change the face of an entire area. Once a forest canopy is damaged, a once cool, damp, and shady area may become a sun-filled, hot, and dry space—effectively creating new habitat for some invasive species while destroying ideal conditions for other, longer-term inhabitants.
Wetland, dune, and beach loss
Storm surge, waves, and winds can destroy wetlands and erode dunes and beaches, which provide critical habitat and important nesting grounds for a wide variety of wildlife species. These areas provide a first line of defense from storm surge for us humans as well. Wetlands alone prevented an estimated $625 million in flood damage to East Coast communities during Hurricane Sandy.
Heavy rainfall and flooding can wash everything from soil and sediment to nutrient pollution to hazardous waste from wastewater treatment plants, refineries, and Superfund sites into marine, coastal, and freshwater environments. The introduction of mud and debris can smother marine life, such as oysters, and damage grasses and agriculture; poisonous contaminants can accumulate in fish and shellfish (and then be eaten by us); and nutrient pollution can contribute to coral bleaching.
What Causes a Hurricane?
Whether you call them hurricanes, typhoons, or cyclones, these systems result from the interplay of four main ingredients: warm ocean water, cooperative wind patterns, stormy weather, and a dose of bad luck (since the first three ingredients alone aren’t always enough).
How Do Hurricanes Form?
While any tropical disturbance can spawn a hurricane, the origins of nearly 85 percent of major Atlantic hurricanes (category 3 and up) come from north Africa, where the Sahara’s scorching summer heat meets the cooler, more humid air that rises from west Africa’s forested coastal regions. The contrast in temperatures forms an area of strong high-altitude winds known as the African easterly jet, which moves from east to west. Because of the difference in land temperatures over which it crosses, the jet wobbles from north to south, creating atmospheric troughs—basically V-shaped tropical waves—of low-pressure areas that get pushed along by the winds. These tropical waves, which can trigger clusters of thunderstorms, emerge near the Cape Verde Islands, just west of Africa (hence the term Cape Verde hurricane) and continue westward across the Atlantic Ocean.
About 60 tropical waves typically track across the Atlantic Ocean each year, peaking in summer and early fall—around the same time that the ocean is at its warmest. And that’s the kicker: When seawater with a temperature of at least 80 degrees Fahrenheit and a depth of about 165 feet meets a low-level weather disturbance like a tropical wave, conditions grow favorable for hurricane development. As a storm system moves across tropical ocean waters, the evaporation of warm water pushes more moist air up into the clouds, creating a low-pressure pocket near the sea’s surface and fueling the storm. Like water going down a drain (but inverted), moist air from surrounding areas rushes in to fill the atmospheric void, then evaporates as well, further fueling the formation of clouds and thunderstorms. As winds pick up and the energy-generating process continues, what was once a tropical disturbance can develop into a tropical depression and then a full-blown hurricane.
Hurricanes and Climate Change
As we continue to heat the planet by burning fossil fuels, we’re altering both the earth’s longer-term climate systems and its shorter-term weather, increasing the threat and cost of extreme weather events. Here’s a look at how the consequences of climate change—and global warming, in particular—affect hurricanes.
How Does Climate Change Affect Hurricanes?
Warmer ocean temperatures
Over the past 50-plus years, the earth’s oceans have absorbed more than 90 percent of the extra heat generated by man-made global warming, becoming warmer as a result. Since warm sea surface temperatures fuel hurricanes, a greater temperature increase means more energy, and that allows these storms to pack a bigger punch. Indeed, some weather analysts suggest a link between the intensity of Hurricane Florence—a Cape Verde storm that drowned the Carolinas with record-breaking rains—and warmer-than-normal Atlantic waters.
Rising air temperatures
The burning of fossil fuels and other human activities have caused an estimated 1 degree Celsius (1.8 degrees Fahrenheit) of global warming since preindustrial times. Since a hotter atmosphere can hold—and then dump—more water vapor, a continued rise in air temperature is expected to result in storms that are up to 15 percent wetter for every 3.6 degrees Fahrenheit of warming, meaning an even greater capacity to generate flooding.
Sea level rise
As the ocean warms and expands and as terrestrial glaciers and ice sheets melt, sea levels are expected to continue to rise. That increases the threat of storm surge—when powerful winds drive a wall of ocean water onto land—for coastal areas and low-lying nations. Hurricane Katrina’s 28-foot storm surge overwhelmed the levees around New Orleans in 2005, unleashing a devastating flood across much of the city.
Research suggests that global warming is weakening the atmospheric currents that keep weather systems like hurricanes moving, resulting in storms that linger longer. Sluggish storms can prove disastrous—even without catastrophic winds—since they can heap tremendous amounts of rain on a region over a longer period of time. The stalling of Hurricane Harvey over Texas in 2017, as well as the slow pace of Hurricane Florence, helped make them the storms with the greatest amount of rainfall in 70 years.
Have Hurricanes Increased in Number?
While there may seem to be a growing number of hurricanes snatching headlines each year, the Intergovernmental Panel on Climate Change (IPCC) does not see a general global trend toward increasing hurricane frequency over the past century. The exception is the North Atlantic, which the United Nations body notes has seen an increase in the frequency and intensity of its hurricanes—though as some researchers note, the uptick may be due in part to improvements in monitoring. Looking forward, the IPCC projects that while there might be a slight decrease in hurricane frequency through 2100, the storms that do make landfall are more likely to be intense—category 4 or 5—with more rain and wind.
Are Hurricanes Getting More Intense?
We may not be experiencing more storms, but we are riding out stronger ones, with heavier rainfall and more powerful winds (hence all those news headlines). Recent research, for example, estimates that Hurricane Harvey dumped as much as 38 percent more rain that it would have without climate change. Another Harvey analysis indicates that the likelihood of a storm of its size evolved from once per century at the end of the 20th century to once every 16-years by 2017—again, due to climate change. Looking forward, the intensity of hurricanes that make landfall is expected to increase through the end of this century, with more category 4 and 5 storms.
As the evidence makes clear, the force, strength, and impact of today’s natural disasters is inextricably tied to society’s past choices. Our centuries-long reliance on dirty fossil fuels has driven the global warming trend, and we’re now experiencing the repercussions in the form of more severe weather events, including catastrophic hurricanes.
Of course, hurricanes are natural phenomena, and there is nothing we can do to halt any single storm in its path (though some people may try). We can, however, forgo the burning of carbon-emitting oil, coal, and gas for more efficient renewable energy options—such as wind and solar—and thereby reduce future warming and the ferocity of tomorrow’s storms.
And that’s a big point of the Paris Agreement, which was signed by nearly every nation on earth in 2015 and aims to curb the consequences of climate change by limiting global warming since preindustrial times to, ideally, 1.5 degrees Celsius. But getting there will require serious heavy lifting in the form of immediate, transformative global action, as the IPCC noted recently in a stark report drafted by some 91 climate scientists representing 40 countries. It will mean slashing global carbon emissions by nearly half by 2030, relative to 2010 levels, zeroing out emissions entirely by about 2050, and meeting as much as 87 percent of global energy needs with renewable sources. The alternative, as laid out by the IPCC, is clear: With a business-as-usual approach, the “extreme” weather of today will seem commonplace by tomorrow.
Think Globally, Act Locally
Unfortunately, the Trump administration ignores the overwhelming evidence from climate scientists worldwide and has instead chosen to double down on fossil fuels and undermine policies designed to reduce carbon emissions and boost clean energy. The administration has committed to withdraw from the Paris Agreement, ditch carbon-cutting policies such as the Clean Power Plan, weaken fuel efficiency standards for cars, and roll back wide-ranging environmental safeguards.
But while the Trump administration is shirking its climate responsibilities, many American leaders—and much of the rest of the world—are pushing ahead. Mayors, governors, companies, and utilities are charting their own course, finding ways to tackle climate change.
That’s where individuals come in, too—especially everyday Americans, who on average produce nearly four times more carbon pollution than citizens elsewhere. As customers, we can support companies invested in meaningful climate action. As U.S. citizens, we can urge political leaders to prioritize clean energy and energy efficiency. And as global citizens, we can take myriad steps to slash carbon pollution from our own daily lives. As the IPCC report shows, there’s still enormous work to be done, but it is only the ramping up of these efforts that will move the needle on climate change.
Reduce Damage and Loss
While we may not be able to prevent the next hurricane, there are ways to reduce the widespread destruction these storms leave in their wake. First, communities, cities, and states should work together to improve climate resiliency and ensure that public safety is a primary factor in determining where and what we build.
A critical component of this effort would be an overhaul of the NFIP, the federal flood insurance program that covers more than five million property holders and incentivizes the rebuilding of properties in flood-prone areas rather than helping victims move out of harm’s way. More than 30,000 U.S. properties have been flooded an average of five times each (with some homes flooded 30-plus times) and then reconstructed with the aid of NFIP. With some commonsense reforms, such as helping homeowners relocate, updating flood maps to reflect new climate realities (including sea level rise and its effects on local storm surge levels), and sharing data on flood hazards, the program could better keep America safe and dry.
Another way to build hurricane resiliency would be to reinstate the Obama administration’s 2015 federal flood protection standard, designed to keep communities safe and to reduce damages from natural disasters. The program, which President Trump scrapped, ensured that any new, federally funded infrastructure projects, such as schools, hospitals, public housing, and police stations, would be built outside flood-prone areas or at least made more resistant to flooding.
Measures such as these could result in major cost savings. Indeed, according to a report by the National Institute of Building Sciences, every $1 spent by the federal government on hazard mitigation today—for example, reducing the number of homes in flood-prone areas and increasing the weather resilience of buildings—could save $6 in future disaster-related expenses.
How to Prepare for a Hurricane
If you live in an area considered at risk for hurricanes, knowing what to do before, during, and after a storm will go a long way toward keeping you safe. Below are a handful of hurricane safety tips.
Hurricane Preparedness List
- Put an emergency action plan in place to ensure that you and your family know what to do, where to go, and whom to contact in case of a hurricane.
- Visit your local government website to find out if you live in a hurricane evacuation area and to familiarize yourself with your area’s evacuation plans, routes, and shelters.
- Prepare a disaster supply kit with enough water and food to sustain your family and pets for three days, plus basic household items such as power sources and a first-aid kit.
- Before a storm hits, add last-minute essentials such as medications, important documents and medical records, and cash, which can prove essential if the power goes out.
- If a storm is possible, fill the gas tank for vehicle or generator in advance.
- Review your homeowner’s insurance policy, and consider insuring your property against the extreme weather events you may face in your area.
- At the start of hurricane season, inspect your home for vulnerabilities. Fix loose shingles, clear drains and gutters, and remove tree branches that could pose a threat during high winds and heavy rain.
- To avoid flood damage, consider home improvements such as elevating boilers and central air-conditioning units, installing a sewer backflow valve, and landscaping to guide water away from your house.
- Before a hurricane’s arrival, secure your property by protecting windows with hurricane shutters or plywood and removing outdoor furniture, trash cans, and other items that could blow away.
- Sign up for local weather alerts to stay on top of storm developments. And keep in mind this key terminology: A “hurricane watch” indicates a storm may happen within 48 hours, while a “hurricane warning” means a storm is expected within 36 hours.
What to Do During a Hurricane
Before, during, and after a storm, follow the instructions of local authorities. If told to evacuate, do so immediately. As a storm develops, evacuation routes may close.
If forced to weather a storm in place, stay away from windows, skylights, and glass doors. Head to an interior room, bathroom, or closet. If floodwaters are a threat, head to the highest floor—excluding closed attics, where you could be trapped if floodwaters go high enough. Do not operate gasoline-powered machinery such as generators inside.
Remain indoors until officials give the “all clear” on a local website or a radio or television station. If you do venture outside, avoid floodwaters, which may contain dangerous debris or hide downed power lines. And remember: Six inches of fast-moving water can sweep you off your feet, and just one foot of moving water can wash a vehicle away. Finally, if you’re feeling emotional distress, don’t hesitate to reach out for help.
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