A hurricane – one of Earth’s most extreme weather events – forms in the tropical ocean, and is powered by heat drawn up from the surface. Hurricanes have affected people since the dawn of time but – due to global warming – their frequency and intensity are increasing.
- What Is A Hurricane?
- What Is The Difference Between A Hurricane, Cyclone and Typhoon?
- How Do Hurricanes Form?
- Can Two Hurricanes Collide?
- Hurricane Categories
- How Are Hurricanes Named?
- Top 10 Worst Extreme Weather Events
- What Are The Dangers of Hurricanes?
- Is Climate Change Making Storms Worse?
- What Damage Do Hurricanes Cause?
- When Is the Hurricane Season?
- Hurricane Forecasting
What Is A Hurricane?
Hurricanes are the most violent weather events ever seen, and yet they are a natural part of Earth’s climate system around the world.
These massive, swirling tropical storms can reach 10 miles high and 1,000 miles across.
Hurricanes only ever form over the ocean near the equator. This is because they need warm, moist air and water as fuel. So when a hurricane reaches land, the force of the storm begins to die down.
The definition of a hurricane is a storm with winds of 119 kilometers per hour (74 mph) or greater. Winds are usually accompanied by rain, thunder and lightning. Hurricanes can last as long as three weeks.
The Eye of a Hurricane
Hurricanes have an area of low pressure in the center called the eye. Immediately surrounding the eye, is the eye wall. Spiraling and swirling out from the wall are clouds called rainbands. The rainbands contain violent thunderstorms with strong updrafts and downdrafts.
If you were standing in the eye of a hurricane, you could be fooled into thinking the hurricane has suddenly stopped. Generally, there are no clouds or wind, the sun comes out and you can see clearly all the way up into space. However, the eye wall is where winds are the fastest and most destructive, and as the hurricane passes on, the relief is short-lived and the storm can explode around you.
What Is The Difference Between A Hurricane, Cyclone and Typhoon?
Nothing. They are exactly the same phenomena, it’s simply that different names are used when they originate in different parts of the world. So, for example, a typhoon is simply a hurricane that forms in the Northwest Pacific Ocean.
Hurricanes: Form in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E.
Typhoons: Form in the Northwest Pacific Ocean, west of the dateline.
Cyclones: Form in the South Pacific and Indian Oceans.
Whatever they are called, these ocean storms all form in the same way.
How Do Hurricanes Form?
Meteorologists have divided the development and life cycle of a hurricane into the following four stages:
Stage 1: Tropical Disturbance
A tropical disturbance is the birth of a hurricane. The first ingredient for a disturbance is warm water, which is why hurricanes only form in tropical regions where the ocean is at least 26.5 degrees Celsius (80 degrees Fahrenheit).
The second ingredient is wind. In storms that form in the Atlantic Ocean, winds blowing from Africa provide the necessary fuel. As wind blows over the warm ocean surface, the water evaporates into water vapor and rises.
As the water vapor rises, it cools and condenses into a large column of cumulonimbus clouds. Evaporation and condensation continue building the column higher and wider. A pattern develops with wind circulating around the center, like water going down a drain. As the moving column encounters more clouds, it becomes a cluster of thunderstorm clouds, called a tropical disturbance. (See also: The Water Cycle Explained.)
Stage 2: Tropical Depression
When winds near the center reach 25 mph, the storm is called a tropical depression. At this stage, the storm begins to look slightly more circular although it has not yet developed an eye.
When seen from a satellite, tropical depressions appear to have little organization. However, a slight amount of rotation can usually be found when looking at a series of satellite images.
As the thunderstorms grow higher, the air at the top of the cloud column starts to cool and becomes unstable. A change in pressure creates more thunderstorms and the storm cloud column spins faster and faster.
Once a disturbance reaches this stage – the amount of time to reach the next stage – tropical storm – can take as little as half a day or as much as a couple of days. Or it may not happen at all.
In August, 2005 a tropical depression grew into one of the most-destructive hurricane storms in American history – Hurricane Katrina.
Stage 3: Tropical Storm
When wind speeds reach 39 mph, the tropical depression becomes a tropical storm. This is also when the storm is given a name.
The rotation of a tropical storm is more recognizable as a hurricane. As the storm system rotates faster and faster, an eye forms in the center. Winds blow around the eye, the calm center of the storm.
If the storm forms north of the equator, it spins counterclockwise. If it forms south of the equator, it spins clockwise. This difference is because of Earth’s rotation on its axis, and the phenomenon is known as the Coriolis effect.
Tropical storms can cause immense damage without ever becoming a hurricane. Most of the problems caused by a tropical storm come from its heavy rainfall.
Stage 4: Hurricane
When wind speeds reach 74 mph, the storm is officially a hurricane. The storm is now at least 10 miles high, reaching well into the troposphere and around 125 miles across. The eye of the storm is around 5 to 30 miles wide.
Hurricanes usually weaken when they hit land, because they are no longer fed by the energy from the warm ocean waters. However, they can move far inland dumping huge amounts of rainfall and causing wind damage before they die out completely.
Did You Know?
Hurricanes cool the surface of the ocean. This is because hurricanes transfer heat from water to the atmosphere. Hurricane Katrina for example caused ocean temperatures to drop by more than 7 degrees Fahrenheit.
Can Two Hurricanes Collide?
Yes. If two hurricanes are within 900 miles of each other they can start to orbit around each other. This is known as the Fujiwhara Effect, first described in 1921 by Sakuhei Fujiwhara, who was director of the Central Meteorological Observatory of Japan.
If they pass within 190 miles of each other then they will collide or merge. This can result in two smaller storms or one much bigger storm. In rare instances, such as with hurricanes Hilary and Irwin it can throw a storm off course completely.
The Fujiwhara Effect is rare in the Gulf of Mexico but relatively common in the western Pacific.
What Was The Most Powerful Hurricane in History?
In 1961, Typhoon Nancy achieved sustained winds of 213 miles per hour with a central low pressure of 882 millibars. Fortunately by the time it hit land in Japan, Nancy had reduced to a category 2 hurricane. It cost $500 million and caused 200 deaths. 1
Hurricanes are rated on a scale of 1 to 5, using the Saffir-Simpson Hurricane Wind Scale. This scale is based on the hurricane’s wind speed and estimates the potential loss of life and damage to property. 2
|Category||Wind.Speed/mph||Damage at Landfall||Details|
|Minimal||Very dangerous winds will produce some damage:|
Possible damage to roof and gutters in well-constructed frame homes.
Large tree branches can snap and shallowly rooted trees fall.
Extensive damage to power lines can cause power outages that could last a few to several days.
|Moderate||Extremely dangerous winds will cause extensive damage: |
Possible major damage to roof of well-constructed frame homes.
Many shallowly rooted trees will snap, uproot and block numerous roads.
Near-total power loss is expected with outages that could last from several days to weeks.
|Extensive||Devastating damage will occur: |
Well-built framed homes can incur major damage or removal of roof decking and gable ends.
Many trees will be snapped or uprooted, blocking numerous roads.
Electricity and water will be unavailable for several days to weeks after the storm passes.
|Extreme||Catastrophic damage will occur: |
Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls.
Most trees will be snapped or uprooted and power poles downed.
Fallen trees and power poles will isolate residential areas.
Power outages will last weeks to possibly months.
Most of the area will be uninhabitable for weeks or months.
|Catastrophic||Catastrophic damage will occur: |
A high percentage of framed homes will be destroyed, with total roof failure and wall collapse.
Fallen trees and power poles will isolate residential areas.
Power outages will last for weeks to possibly months.
Most of the area will be uninhabitable for weeks or months.
How Are Hurricanes Named?
The World Meteorological Organization (WMO) is responsible for the lists of hurricane names. This is specific to storms that start in the North Atlantic Ocean. Other lists are in place for storms in the Pacific Ocean, the Indian Ocean and across Australasia.
The WMO has six lists, each with the name of 21 female and 21 male names. The lists are used in rotation and recycled every six years. When a hurricane is particularly damaging, like Katrina (2005), Irma (2017) and Florence (2018) – that name is retired. When a name is removed, the WHO replace it with another. For example, Katia is the replacement for Katrina.
Retired hurricane names in East Pacific include Pauline (1997), Patricia (2015) and Manuel (2013).
Retired hurricane names in Central Pacific include Paka (1997).
Top 10 Worst Extreme Weather Events
The following table provides a list of the world’s Top 10 climate-related disasters for absolute losses. Hurricanes account for the top five disasters.
|Hurricane Katrina – Sept 2005||USA||156|
|Hurricane Harvey – Aug 2017||USA||95|
|Hurricane Irma – Sept 2017||USA & Caribbean||80|
|Hurricane Maria – Sept 2017||Caribbean & USA||69|
|Hurricane Sandy – Oct 2012||USA & Caribbean||53|
|Floods – July & Aug 1998||China||44|
|Floods – Aug 2011 to Jan 2012||Thailand||43|
|Hurricane Ike – Sept 2004||USA & Caribbean||36|
|Hurricane Ivan – Sept 2004||USA, Caribbean, Venezuela||29|
|Hurricane Wilma – Oct 2005||USA, Mexico, Belize, Honduras, Caribbean||25|
What Are The Dangers of Hurricanes?
Every hurricane is different and can cause a variety of unique and life-threatening hazards to a given location.
Hurricane wind speeds can reach up to 155 mph (250 km/h), with gusts that exceed 224 mph (360 km/h). The danger to life and property is either a result of direct impact of the wind or by flying debris. The wind can damage crops, flatten entire forests, shake and even collapse tall buildings. The atmospheric or barometric pressure differences inside a hurricane can suck up a roof or entire building.
The rains that accompany hurricanes are difficult to predict. They can last several days or just a few hours. If rain is persistent and heavy it can cause structures to collapse with the weight of the absorbed water. Inland flooding can damage roads and bridges.
Landslides are a secondary hazard, particularly in areas where there are steep slopes. As part of their climate change adaptation strategy, governments are looking for ways to make their coastal towns and cities more ‘water-proof’. This includes the use of green construction and the creation of so-called Sponge Cities, where climate change challenges are taken into account in architectural design.
While hurricanes are known for destructive winds, usually a hurricane storm surge is the greatest threat.
A storm surge is a temporary rise in sea level causes by water been driven on-shore by hurricane winds. Storm surges present the greatest risk to coastal communities. 90 percent of hurricane fatalities are due to drowning caused by storm surges 4
If a storm surge hits normal high tide, it can rear up to 20 feet or more – causing extreme floods in coastal areas.
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. 5
Tornadoes are another occasional feature of hurricanes. Usually, they start on the fringes of hurricanes – the outer rainbands – which contain convective cells – thunderstorms – of their own. As long as a hurricane is over water, a tornado will not form. It is only when over land, where surface friction is higher, that a twister can be produced. Usually, tornadoes produced by hurricanes are relatively weak and short-lived, but they still pose a threat.
Which Is The Deadliest Hurricane Ever?
The deadliest Atlantic hurricane in recorded history was the Great Hurricane of 1780, which killed over 22,000 people. It struck Barbados most likely as a Category 5 hurricane.
In modern times, the deadliest hurricane was Hurricane Mitch in 1998 which hit central America and killed at least 11,000 people.
Is Climate Change Making Storms Worse?
Yes. Climate change is increasing both the frequency and severity of hurricanes, cyclones and typhoons. A recent study by NOAA shows that the odds of Category 3, 4 and 5 hurricanes are increasing because of human-caused global warming. This finding builds on previous research which had identified a trend, but was not statistically robust. 6
This connection – between hurricanes and climate – is hardly surprising. Hurricanes are powered by warm ocean water, and climate change causes significant ocean warming in the upper layers.
In addition, climate change is a major driver of sea level rise, which gives storm surges a higher starting point. This can exacerbate the destructive power of the hurricane when it makes landfall.
Given that hurricanes get their energy from warm ocean waters and water vapor in the air, these findings are consistent with what scientists expect to happen as the world warms. For example, we now know that the rainfall from Hurricane Harvey was 15 percent more intense and three times as likely to occur, because of anthropogenic climate change.
For more, see: Effect of Global Warming on the Oceans.
What Damage Do Hurricanes Cause?
Loss of Life
Hurricane Katrina which flooded the coastal communities of Mississippi and Louisiana in 2005 killed more than 1,500 people in New Orleans alone, and caused millions of dollars in damage. Homes, schools, hospitals and businesses were destroyed.
The above chart gives the breakdown of how people died in hurricanes between 1963 and 2012. It shows that roughly 90 percent of deaths occurred in water-related incidents, mostly by drowning. Storm surge was responsible for about half of the fatalities (49 percent). Floods and mudslides induced by rainfall accounted for 27 percent of deaths. Between 100 and 150 people perished near the shoreline from rip currents, large waves, etc. About the same number, drowned in marine incidents offshore. About 3 percent of victims died in tornadoes.
Global natural disasters exacerbated by the climate crisis, caused $210 billion in losses in 2020 as several countries, including the United States, Australia and China, battled hurricanes, floods and wildfires. This was up from $166 billion the year before – a jump of 26 percent.
Hurricane Laura, which hit Louisiana in August 2020, was the most destructive event in the United States that year, costing $13 billion. Overall losses from the hurricane season in North America came to $43 billion.
Additionally, severe thunderstorms in the Midwest cost $40 billion in overall losses, up 33 percent compared to 2019. 7
When a major hurricane comes ashore, the effects ripple throughout the economy. The United States, with thousands of miles of shoreline, is particularly vulnerable to hurricane damage. Coastlines are an important part of the economic engine. According to the National Oceanic and Atmospheric Administration (NOAA), coastal counties create 40 percent of America’s jobs and they are responsible for 46 percent of the nation’s GDP.
Unfortunately, the continued warming of the earth’s climate system means that we can expect more severe and destructive cycles of droughts, flooding and hurricanes, all of which are influenced by the combined effect of (a) rising temperatures over land, (b) decreased equator-versus-pole temperature differences, and (c) increased humidity. 8
Furthermore, individual hurricanes will cause even more rainfall in the future since warmer air can hold more water vapor. 9
High wind and rainfall associated with hurricanes can result in severe damage to local ecosystems, causing mortality among wildlife.
However, a hurricane’s after-effects may have a more profound effect on wildlife populations. These include loss of nests, food supplies, increased vulnerability to predators, micro climate changes and increased conflict with humans.
Bird species which require large old trees for roosting or nesting are particularly vulnerable to hurricanes, as these trees are often the first to be uprooted. Loss of forest canopy can also effect the micro climate on the forest floor. 10 11
Positive Effect of Hurricanes on Ocean Life
Scientists have a good understanding of how hurricanes impact the surface layer of water, the sunlight zone where photosynthesis occurs. Strong winds churn colder water from below, bringing up nutrients like phosphorus and nitrogen which can stimulate growth of phytoplankton algae. Technically this is termed nutrient upwelling into the photic zone.
What scientists know less about, is the deep ocean. But there is now evidence that hurricanes also affect the ocean’s biological pump.
Organic material from the upper ocean is carried deep down into the ocean during the storm. This provides a big boost for marine-life biomes where sunlight doesn’t reach. For example, October 2016, Hurricane Nicole increased zooplankton and microbial biomass by 30–300 percent at 1,500 m depth and 30–800 percent at 3,200 m depth.
When Is the Hurricane Season?
The Atlantic season officially runs from June 1 to November 30. In the East Pacific, it runs from May 15 to November 30. Hurricanes have occurred outside of the official season, but these 6 months encompass over 97 percent of tropical activity. 13
On average the Atlantic hurricane season has 12 named storms and 6 hurricanes, according to NOAA.
In 2020, the season saw 30 named storms, 13 of which were hurricanes.
Meteorologists use data from satellites, ships, reconnaissance aircraft and land based platforms such as radars to monitor storm activity. Warnings are issued by NOAA’s National Hurricane Center (NHC) and other hurricane forecast centers around the world. Data observations are fed into a climate model to make predictions.
Hurricane Technical Terms
Central Dense Overcast (CDO): A dense cirrus cloud pattern that forms near the center of a tropical storm and its rainbands. It is also known as the eye wall. CDO can be seen in satellite photos and is the hall mark of an intensifying tropical storm. Once a storm reaches the hurricane strength threshold, usually an eye can be seen in either the infrared or visible channels of the satellites. The eye can be clear of clouds (clear eye) or it can be filled with low and mid level clouds (filled eye).
Tropical Upper Tropospheric Trough (TUTT): A trough is an elongated region of low atmospheric pressure. TUTT is a trough situated in the upper-level of the tropics, and TUTT movement affects the formation of tropical cyclones. TUTTs are important for tropical cyclone forecasting as they can force large amounts of vertical wind shear over tropical disturbances and cyclones slowing down their strengthening. They can also do the opposite, intensifying tropical cyclone genesis by providing for an efficient outflow channel in the upper troposphere and by providing additional force near the storm center. 14
Dvorak Technique: The Dvorak technique is a way to estimate a tropical cyclone’s intensity from satellite pictures. A tropical cyclone satellite image is compared to other possible pattern types: Shear Pattern, Eye Pattern, Curved band Pattern, Central Dense Overcast (CDO) Pattern, Embedded Center Pattern or Central Cold Cover Pattern.
If infrared satellite imagery is available, this can be used to analyze the difference between the temperature of the warm eye and the surrounding cold cloud tops. The larger the difference, the more intense the tropical cyclone is likely to be. From this, scientists get a “T-number” and a “Current Intensity (CI) Number”.
- “The 10 Most Powerful Hurricanes, Cyclones, and Typhoons in History.” Thoughtco.
- CRED and UNISDR Report – https://www.preventionweb.net/files/61119_credeconomiclosses.pdf
- Edward N. Rappaport. 2014. How Hurricanes Kill People.
- “Storm Surge”: A storm surge is a rise in sea level that occurs during tropical cyclones, intense storms also known as typhoons or hurricanes. National Geographic.
- “Global increase in major tropical cyclone exceedance probability over the past four decades.” J.P. Kossin et al. June 2020.
- “Natural Disasters Cost $210 Billion Worldwide in 2020” 2020 losses were up 26.5% from 2019. Investopedia. January 2021.
- Field, 2012.
- Emanuel, 2017.)
- “Effects of hurricanes on wildlife: implications and strategies for management.” Joseph M et al. 2018.
- “Long‐term population dynamics reveal that survival and recruitment of tropical boobies improve after a hurricane.” Sergio Ancona et al. 2016.
- “Hurricanes Enhance Labile Carbon Export to the Deep Ocean.” R. Pedrosa‐Pàmies et al. 2019.
- “Hurricane Season Information.” NOAA’s Atlantic Oceanographic and Meterological Laboratory.
- See also: “How Do the Monsoon Trough and the Tropical Upper-Tropospheric Trough Affect Synoptic-Scale Waves: A Comparative Study.” Tao Feng et al. 2020.