What Causes Hurricanes? How are They Formed?

© FotoKina/Shutterstock.com

Written by Dayva Segal

Updated: October 1, 2023

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Hurricanes are powerful storms, capable of tearing through communities and damaging neighborhoods beyond repair. To make matters worse, these storms often bring additional risks, like storm surge and tornadoes. Luckily, advanced warning systems typically give residents plenty of time to evacuate. However, some hurricanes, like Hurricane Katrina and Hurricane Harvey, have caused billions of dollars of damage, destroyed homes, and taken countless lives.

Ninth Ward New Orleans post-Hurricane Katrina

In 2005, Hurricane Katrina decimated New Orleans. The city’s Ninth Ward was hit particularly hard.

©Marc Pagani Photography/Shutterstock.com

What is a Hurricane?

Technically, hurricanes are a type of tropical cyclone. When one of these powerful storms forms over the Atlantic Ocean or the Northeastern Pacific Ocean, it is called a hurricane. Hurricanes that formed over the Atlantic Ocean are often called Atlantic Hurricanes, while those formed over the Pacific Ocean are often called Pacific Hurricanes.

When a tropical cyclone occurs in the Northwestern Pacific Ocean, Indian Ocean, South Pacific Ocean, or South Atlantic Ocean, it is called a typhoon.

Other names for tropical cyclones include:

  • Cyclonic storm
  • Tropical storm
  • Tropical depression
  • Cyclone

What Is a Tropical Cyclone?

Tropical cyclones are complex storms that have a center of low air pressure. The storm rotates rapidly around this center. Around the center, the storm has high winds, thunderstorms, and heavy rain. However, the center, also known as the eye of the storm, is often eerily calm.

Fun fact: All cyclonic storms spin counterclockwise in the northern hemisphere and clockwise in the southern hemisphere due to the earth’s rotation.

Tropical cyclones get their name from their spinning nature and the places where they usually form – tropical seas. They get their fuel from warm tropical water.

What Causes a Hurricane?

Hurricanes (and other tropical cyclones) are caused by a confluence of events creating “the perfect storm.” It starts as a simple low-pressure area over a warm ocean. In low-pressure areas, the air is thinner. Wind tends to blow into low-pressure areas because there is less resistance. In the case of a hurricane, the warm and moist ocean air from condensation and evaporation is sucked up into this low-pressure area. The air rises, forming clouds. But then, it cools off since it is no longer close to the warm water. This creates clouds and thunderstorms, eventually forming a hurricane.

Trade winds blowing towards the west push Atlantic Hurricanes towards the Caribbean, Central America, and the eastern and southern coast of the United States as they are forming.

Hurricane Katrina as seen from space

Hurricanes spin counterclockwise, the direction all cyclonic storms turn in the Northern Hemisphere.

©LiL SUS/Shutterstock.com

Do Hurricanes Like Warm or Cold Water?

Most experts agree that the ocean must be between 79- and 81-degrees Fahrenheit to form a tropical disturbance that will eventually turn into a hurricane. If the ocean is warmer than that, the storm may become more intense, or form even more quickly than usual.

When and How Often Do Hurricanes Form?

Hurricanes, as well as other types of tropical cyclones mainly form in the summer months, when the ocean is warmest. However, there have been tropical disturbances and depressions that have formed at any time of year, and hurricanes and tropical storms have formed in the winter months.

The Atlantic hurricane season is officially from June 1 to November 30.

During an average hurricane season, there are at least 12 named storms, meaning at least 12 tropical disturbances that eventually turned into a tropical storm or hurricane.

Where Do Hurricanes Form?

Even though hurricanes form close to the equator, due to the earth’s tilt and rotation, they cannot form within five degrees of the equator. Within that area, there is not enough force to cause the storm to spin.

Atlantic Hurricanes often start in Africa and then get fueled by warm tropical waters after being blown west by winds.

How do Hurricanes Form?

There are four stages to a hurricane’s formation.

Tropical Disturbance

First, the evaporated moisture and warm air from the ocean rise to form clouds as described above. This happens in a cycle, until a pattern of rotating winds develops, due to the way the air moves into the low-pressure system. Once it is a cluster of thunderstorms, it is called a tropical disturbance.

Tropical Depression

These patterns of growing clouds, higher winds, and more thunderstorms continue as the warm air on the ocean’s surface continues to enter the low-pressure area. The storm spins faster, establishing the rotational motion even further. When the wind speed is 25 miles per hour, the storm becomes a tropical storm.

Tropical Storm

As the storm continues to gain steam, fueled by warm ocean water and warm air near the surface of the ocean, the winds pick up further. Once they reach 39 miles per hour, it becomes a tropical storm. Once this happens, it is given a name. This stage is also when the eye of the storm forms more clearly, and the winds establish a rotational pattern around the eye.


When one of these rotating storms reaches wind speeds of 74 miles per hour, it is now officially a hurricane. The trade winds usually keep pushing Atlantic hurricanes westward until they make landfall. As they move further inland, they get weaker without the warm ocean water and air to fuel them. However, even as they weaken back into a tropical storm, they can still wreak havoc with high winds and heavy rain.

How Big Is a Hurricane?

In addition to having high winds of at least 74 miles per hour, a hurricane is also usually around 50,000 feet high and at least 125 miles wide. The largest cyclonic storm ever was Typhoon Tip, which had a diameter of 1,380 miles. The largest Atlantic hurricane was Hurricane Sandy, which was at least 1,000 miles in diameter. That may be the reason it caused so much widespread damage despite it being only a category 1 hurricane.

What Are Hurricane Categories?

Atlantic and Pacific hurricanes are categorized using the Saffir-Simpson Scale, which determines the likelihood of damage to property or people. This scale only measures wind speed. However, even storms with relatively low wind speeds can cause a lot of damage from flooding, tornadoes, or storm surges.

  • Category 1: Winds between 74 and 95 mph. Minimal damage. Some damage to roofs and home exteriors. Tree branches may fall. Power may be out for a few days due to damage to power lines.
  • Category 2: Winds between 96 and 110 miles per hour. Moderate damage. Homes may sustain significant damage. Small trees may become uprooted. Power will be out for a few days to a few weeks.
  • Category 3: Winds between 111 and 129 mph. Extensive damage. Many homes will be severely damaged. Trees may fall, blocking roads. Electricity and fresh water may not be available for a few days to a few weeks.
  • Category 4: Winds between 130 and 156 mph. Extreme damage. Homes may lose roofs and walls. Most trees and power poles will be uprooted. The area may not be inhabitable for a few weeks to a few months.
  • Category 5: Winds of 157 mph or more. Catastrophic damage. Most structures will be destroyed. Most trees and power poles will fall, causing the area to be cut off to road travel and electricity. The area may not be inhabitable for months.

The National Weather Service made a statement that while these wind-based categories are useful tools for people to know how to prepare for a storm, storm surge and expected coastal flooding levels must also be considered. Because of that, they have created several tools for tracking storm surges, including a storm surge risk map so you can determine if you live in a risky area.

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About the Author

Dayva is a writer at A-Z Animals primarily covering astrology, animals, and geography. She has over 12 years of experience as a writer, and graduated from Hofstra University in 2007 with a Bachelor of Science in Music and a Minor in French. She has also completed course work in Core Strengths Coaching, Hypnotherapy, and Technical Communication. Dayva lives in the SF Bay Area with her cute but very shy cat, Tula.

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