Earth's Biggest Storms: Tropical Cyclones
Called hurricanes by some, these spinning megastorms have catastrophic impacts across the globe
On September 5th, 2017, Hurricane Irma made landfall in the Caribbean Islands. The National Hurricane Center reported sustained winds of up to 185 mph (298 km/h) making it one of the most powerful storms on record to hit the Atlantic.
Two weeks later Hurricane Maria made landfall in Puerto Rico, resulting in one the worst natural disasters in the island’s history. The storm resulted in 3,000 fatalities, and incurred millions of dollars in damage to infrastructure.
The environmental impact of Maria was also devastating. Thousands of trees were uprooted or damaged; sand dunes and shorelines shifted, changing the geography of the island. The fragile island ecosystems suffered significant loss of biodiversity.
As Earth’s temperatures rise, scientists predict an increase in the intensity of storm events, including cyclones like Hurricanes Irma and Maria. Read on to learn about these dynamic storms, and how they affect the people and environments in their paths.
While conducting search and rescue in Puerto Rico after Hurricane Maria, a US Customs and Border Protection helicopter located this home ( US Customs and Border Protection ).
UNDERSTANDING CYCLONES
Cyclones, also called hurricanes or typhoons, are intense storms that form over tropical or subtropical waters. These high-energy storms typically form in warm waters between the Tropics of Cancer and Capricorn, which are located at 23.5° latitude north and south of the equator. They don’t, however, form directly over the equator.
In order for a cyclone to form, several environmental conditions must be met. Among the catalysts is a low-pressure system that may accompany rain or a thunderstorm, water warmer than 80° F (27° C), and water depths of at least 150 ft (46 m).
Another key ingredient is wind. As the storm moves over warm surface water, some of that water evaporates into the air. Winds accelerate the evaporation process and push warm, moist air upward, where it begins to cool. The moisture condenses into clouds, eventually forming a thunderstorm. As these winds gain energy, the storm system starts spinning at a low altitudes in a circular motion. According to the National Hurricane Center , when sustained wind speeds reach 74 mph (119 km/h) for over one minute the storm system is considered a cyclone. While cyclones can vary wildly in size, a typical cyclone system averages 300 miles (186 km) in diameter and can reach 10 miles (16 km/h) upward into the atmosphere.
ANATOMY OF A CYCLONE
As a cyclone moves it displaces massive quantities of water. This causes storm surges and flooding when it makes landfall.
As a cyclone hits land, it loses its main source of energy, and eventually winds die down. However, the storm will continue to release significant amounts of moisture contained within the weather system, often causing flooding.
Data on hurricanes has been recorded since the mid-1800s, allowing researchers and meteorologists to study and understand where and how powerful these storms have been. The map below shows the frequency of hurricane events around the world from 1842–2019.
Historical cyclone tracks (1842–2019) provide insights into their frequency and intensity. The tracks in red show the most severe storms; blue tracks are the least intense. The ocean is broken into six basins, each of which has unique monitoring agencies.
Cyclones are seasonal, meaning that regions of the world experience them at different times of the year. From June to November cyclones are most active in the Atlantic Basin. From April to November they're more active in the Pacific and Indian Basins. The animation below shows when and where cyclones occur over the course of an annual cycle.
TROPICAL CYCLONE BASIN TERMINOLOGY
The ocean is divided into six regional basins, with the responsibility for handling oceanic storm event warnings assumed by regional centers. Each regional center has its own slightly different category and classification scales, as shown in the table below.
Earth’s average temperatures have been increasing over the last century. As ocean temperatures also continue to rise, a study published by the National Oceanic & Atmospheric Administration predicts that, among other effects, cyclones will have greater levels of intensity.
Galveston Island, Texas after Category 4 Hurricane Ike on September 13, 2008. ( U.S. Air Force )
HUMAN IMPACT
House on Avenue N after the Great Galveston Hurricane of 1900. ( Library of Congress )
People have always made their homes along coastlines. Cities, towns, and communities inevitably deal with severe storms and their effects with every cyclone season.
“The street railway trestle was carried squarely against the side of the house like a huge battering ram; the house creaked and was carried over in the surging waters and torn to pieces.” —Galveston Weather Station Chief Isaac M. Cline, 1900
How a cyclone affects an area depends on many factors: where it hits, the intensity at landfall, the tidal cycle, the speed the storm is traveling, and the population density of the area.
Every storm behaves differently. Some sidle up to coastlines, moving along slowly or “sitting” and wreaking havoc for extended periods. Other storms come in quickly and move through areas with erratic and rapidly-changing trajectories and intensities. Whether a storm moves quickly or slowly, the people who live in coastal areas experience a dangerous mixture of storm surges, heavy rains, high winds, and even tornadoes.
What are the major impacts for humans?
Storm Surge | Heavy Rain | Flooding | High Wind | Tornado |
---|---|---|---|---|
Abnormal rise of water due to a cyclone's winds can reach heights in excess of 6 meters (20 feet) | Rainfall amounts are related to the local geography and the speed and size of the storm rather than to its strength. | Floods are dangerous and destructive and are the major threat to people from cyclones. | Sheltering or evacuating before the onset of cyclone-level winds is critical for survival. | Tornadoes can occur in thunderstorms, typically enclosed in rain bands away from the center of the storm. |
These surges can travel several miles inland and span hundreds of miles of coastline. | Slow-moving large storms produce more rain. | Flash floods happen when significant rainfall raises water levels rapidly. | These strong winds can destroy entire buildings and mobile homes. | They also can form near the eye wall. |
A storm tide can happen when there is a combination of a storm surge and the astronomical tide. | Mountainous terrain also enhances a storm's rainfall. | Longer-term flooding of rivers and streams can inundate areas for extended periods after the storm. | Home siding and roofing, small items left outside, or signs can turn into flying missiles when cyclone force winds arrive. | While cyclone-spawned tornadoes tend to be less powerful and short-lived, they do still pose a tremendous threat. |
Flooding destroys levees and communities in low-lying areas, while storm surges and strong waves demolish buildings, roads, and beaches. Extreme rains destroy agricultural areas while high winds topple trees and devastate critical infrastructure, crippling areas for extended periods of time. Tornadoes are also fairly common when hurricanes make landfall, causing intense damage to areas that are directly hit.
While landfall removes the energy source of the storm, causing it to lose strength, people inland may still suffer from high winds and heavy rains that create flooding from swollen rivers that can wash out bridges and cause deadly mudslides.
Local crews clear streets of sand from Hurricane Sandy ( FEMA )
From 1998 to 2017 storms caused 233,000 deaths globally, second only to earthquakes in terms of fatalities caused by natural disasters. During the same period 726 million people were directly affected through injuries, homelessness, displacement, and evacuation during the emergency phases of storms.
A World Food Programme helicopter delivers humanitarian aid to Bebedo, Mozambique, following Cyclone Idai. (U.S. Air Force photo by Staff Sgt. Corban Lundborg)
EXCEPTIONAL STORMS
Within the last 15 years Earth has experienced a series of exceptional storms that have had particularly catastrophic impacts for humans.
The following maps show individual cyclone tracks observed at three-hour intervals. Height and color indicate wind speed and category, as shown in the graphic on the left.
ECOSYSTEM IMPACT
Tropical regions, where cyclones are most common, are also known for their biodiversity . Biodiverse ecosystems are home large numbers of species. Scientist think many factors contribute to the biodiversity of the tropics, including their warm, humid climates and relatively stable temperatures. These happen to be the same atmospheric conditions that produce tropical storms.
Combining historical cyclone data with biodiversity information clearly illustrates that some of the regions with the highest biodiversity also experience a high frequency of cyclones.
Regardless of its strength or where it makes landfall, a cyclone alters the ecosystems in its path. From coral reefs to tropical rainforests, life is constantly moving, adapting, and evolving. One of the many evolutionary pressures in these areas are caused by cyclones.
The environmental impacts that Puerto Rico and the other islands in the Caribbean Sea experienced affected humans and many plant and animal species. When hurricanes Maria and Irma hit the region in the fall of 2017, they changed local ecosystems in astounding ways.
Islands once teeming with life were completely devastated. The transformation that occurred over the course of the two storms altered the landscape so dramatically that some areas were almost unrecognizable.
LOST SAND DUNES
Cyclones can move massive quantities of sand due to heavy rain, storm surges, high winds, and widespread flooding. These can transform entire shorelines, moving and redistributing sediment into the ocean.
During Hurricanes Maria and Irma, areas occupied by dunes on the north shore of Puerto Rico were flattened and eroded, washing away sand that was redeposited in the ocean. These dunes are important to humans, protecting man-made infrastructures including roads, homes, and businesses by providing buffer zones between human-populated areas and the ocean.
The dunes protected low-lying areas from flooding during non-catastrophic storms. These dunes were critical for wildlife, providing beach habitat for several species including endangered sea turtles that nested on the shore.
EL YUNQUE TROPICAL RAINFOREST
Nearly 31 million trees were damaged or destroyed after hurricanes Irma and Maria hit Puerto Rico. In El Yunque National Forest , the only tropical forest in the U.S. Forest Service’s system, high-speed winds wreaked havoc. A lush, green old-growth rainforest teeming with life morphed into a brown, muddy mess in just under a month’s time.
The devastating force of Irma and Maria tore through forests, destroying twice as many trees as an average hurricane.
When the winds died down and the skies cleared, roughly 30% of the trees in El Yunque were strewn across the forest floor—a devastating setback for the old-growth forest that had been recovering from logging and the impacts of other storm events.
El Yunque will take years, if not decades, to fully recover from the habitat destruction incurred by Hurricanes Irma and Maria. As the magnitude of hurricanes increase, some wonder if the forest, and the habitat it provides, will ever be the same again.
COMPARING TWO SPECIES
El Yunque National Forest is also the only remaining natural habitat for the endemic Puerto Rican Parrot (Amazona vittata), the only parrot species native to the United States. This parrot relies on rainforest trees for food, and nests in hollow cavities of tall old-growth trees in rainforests. In 1989 Hurricane Hugo wiped out roughly half of the wild population, leaving just 20 birds. Conservation efforts since 1989 increased the wild population of the parrots; however, the severity of recent cyclones is a cause for concern for this species.
An endangered Puerto Rican Parrot and a Caribbean anole lizard. ("Puerto Rican parrot 1" Altered version of photo by Tom MacKenzie, USFWS is licensed under CC BY 2.0 , and Caribbean anole by Colin Donihue )
High speed video of a lizard experiencing hurricane-force winds, and then landing safely in a safety net. ( Colin Donihue )
Natural life on impacted islands is constantly evolving as better-adapted individuals survive these storm events in greater numbers. While some species are fighting a steep uphill battle, others, like the Caribbean anole lizard (Anolis scriptus), are adapting rapidly in surprising ways.
Evolutionary ecologist Colin Donihue had been studying Caribbean anole lizards in the Turks and Caicos Islands, near Puerto Rico, immediately before Hurricanes Irma and Maria.
He returned to the islands shortly after Hurricane Maria and made some interesting discoveries. He found that Caribbean anole lizards that live in locations that experience frequent extreme weather events, such as hurricanes, respond more rapidly to the than those in more sheltered locations.
After Hurricanes Irma and Maria, Donihue’s survey sample of the anoles that survived the hurricane showed the lizards had larger toe pads, longer front legs, and shorter hind legs than their less climate-vulnerable counterparts.
On the end of their fingers and toes, Anolis scriptus lizards have adhesive lamellae that help them cling to surfaces. ( Colin Donihue )
This means that the anoles that survived the storms were able to cling to trees more effectively than anoles with smaller toe pads and longer rear legs that got caught in the wind.
Species with rapid reproductive rates, such as anole lizards, can experience an evolutionary trajectory that holds relatively steady against the forces of hurricanes. The traits that helped this population of anoles survive these storm events will likely continue to be passed on to their offspring.
MOVING FORWARD
Living things affected by storm events are constantly evolving to adapt to the changing conditions—as does technology. We can mitigate storm event damage by taking advantage of advances in our technology.
Conservation efforts to save the Puerto Rican Parrot started decades ago. The ongoing support provided by the people of Puerto Rico improves the odds that this species will make a recovery.
Scientists have been able to use geographic information systems, or GIS, to track parrot populations and the health of their habitat in order to determine the greatest threats to these birds. By analyzing data, biologists are reducing threats, managing conservation efforts and captive breeding programs, and helping to increase parrot populations. The parrots that hatch in protected facilities can then be released into the wild with increased odds of survival.
Progress is being made in the rainforest as well. New plants and trees are returning to storm-scarred areas, turning the forests verdant again.
A Caribbean anole drinks water from a leaf. ( Colin Donihue )
The abundant Caribbean anole lizards will continue to be of interest to scientists. Anole lizards are able to adapt rapidly to changing environmental conditions caused by cyclones. As anoles reproduce quickly, their populations are not at risk of extinction. However, the anoles are providing clues to biologists who are studying how these lizards adapt. These clues may be able to help us learn how better to support other species in the aftermath of natural disasters.
HUMAN RESILIENCY
As for human impacts in cyclone-affected areas, we can also be hopeful. By using constantly-evolving technology, humans are able to help other people, sometimes even from thousands of miles away.
Residents of Loíza, Puerto Rico, attending an event to prepare the community for the 2019 hurricane season. ( FEMA/Eduardo Martínez )
If you live in a cyclone-prone area, the best time to prepare is now. Having a plan in place ahead of time will help ensure your safety in the event that you need to evacuate, reinforce parts of your home, or take other actions.
TECHNICAL ADVANCEMENTS
Two USGS hydrologic technicians install rapid water gauge devices to measure water levels in preparation for storms. ( Chris Henry, USGS )
Weather forecasters and government agencies continue to advance their predictive models to improve the accuracy of storm forecasts. For example, these models include calculating the maximum extent of storm surges and their resulting flooding, the cause the most fatalities in cyclones.
These early warnings can help prevent loss of human life by providing more time for people to prepare their homes and to evacuate to safety.
Collecting storm data in real time is another way that GIS is being used. Tracking weather data as storms are happening allows emergency management officials to redirect resources and, if necessary, update warnings.
After Hurricane Maria, a homeowner in Puerto Rico used hurricane-resistant materials to rebuild their house. ( FEMA/Andrea Bajandas )
GIS software also offers opportunities for urban planners to incorporate mitigation plans to minimize and prevent damage from future storms. By using storm-resistant techniques and materials to rebuild homes, businesses, and infrastructure, we can decrease the economic and human costs of future storm events.
The National Weather Service has developed projections for where the most significant damage is likely to happen. Community leaders are now equipped to plan optimal evacuation routes, as well as locate emergency shelters where they will be needed the most.
Hurricanes Irma and Maria have also exposed weaknesses in existing records and data infrastructure. Many places, especially rural areas in the Caribbean, were not well mapped before the hurricanes. In order to provide supplies and assistance, relief workers need accurate maps. When word spread about inadequate maps via media reports, thousands of citizen volunteers from all over the world answered the call for help. Volunteers used satellite imagery and mapping software to add building locations, even adding whole villages to maps using Humanitarian OpenStreetMaps .
Esri's Disaster Response Program helps communities during the emergency stages and recovery from a cyclones hit.
Despite the fact that volunteers may be thousands of miles away from the locations of natural disasters, their contributions are often invaluable. Through technology, hard work, and determination, these volunteers have helped bring hope to areas overwhelmed by cyclones.
Esri’s Disaster Response Program (DRP) assists organizations responding to disasters and crises worldwide as part of its corporate citizenship efforts. The program helps ensure that communities get the help they need to understand current conditions, make better decisions, and respond more effectively during a crisis.
GET INVOLVED
One of the best ways you can help is by directly supporting land and habitat conservation organizations. Other ways to help include advocating for reducing greenhouse gas emissions—and minimizing your carbon footprint—to reduce the rate of climate change.
People interested in volunteering to help map areas affected by disasters can go to the Humanitarian OpenStreetMaps site or support the work the Red Cross Hurricane Relief efforts.