What Causes Hurricanes?

Warm air and warm water combine to create destructive storms

Flooded streets in Hoboken, NJ after Hurricane Sandy
Flooded streets in Hoboken, NJ after Hurricane Sandy. Dennis K. Johnson/Lonely Planet Images/Getty Images

The two essential ingredients in every hurricane are warm water and moist warm air. That’s why hurricanes begin in the tropics.

Many Atlantic hurricanes start to take shape when thunderstorms along the west coast of Africa drift out over warm ocean waters that are at least 80 degrees Fahrenheit (27 degrees Celsius), where they encounter converging winds from around the equator. Others originate from unstable air pockets popping out in the Gulf of Mexico.

Warm Air, Warm Water Make Conditions Right for Hurricanes

Hurricanes start when warm, moist air from the ocean surface begins to rise rapidly, where it encounters cooler air that causes the warm water vapor to condense and to form storm clouds and drops of rain. The condensation also releases latent heat, which warms the cool air above, causing it to rise and make way for more warm humid air from the ocean below.

As this cycle continues, more warm moist air is drawn into the developing storm and more heat is transferred from the surface of the ocean to the atmosphere. This continuing heat exchange creates a wind pattern that spirals around a relatively calm center, like water swirling down a drain.

Converging Winds Create Hurricanes

Converging winds near the surface of the water collide, pushing more water vapor upward, increasing the circulation of warm air, and accelerating the speed of the wind.

At the same time, strong winds blowing steadily at higher altitudes pull the rising warm air away from the storm’s center and send it swirling into the hurricane’s classic cyclone pattern.

High-pressure air at high altitudes, usually above 30,000 feet (9,000 meters), also pull heat away from the storm’s center and cool the rising air.

As high-pressure air is drawn into the low-pressure center of the storm, the speed of the wind continues to increase.

As the storm builds from thunderstorm to hurricane, it passes through three distinct stages based on wind speed:

  • Tropical depression—wind speeds of less than 38 miles per hour (61.15 kilometers per hour)
  • Tropical storm—wind speeds of 39 mph to 73 mph (62.76 kph to 117.48 kph)
  • Hurricane—wind speeds greater than 74 mph (119.09 kph)

Are There Links Between Climate Change and Hurricanes?

Scientists agree on the mechanics of hurricane formation, and they agree that hurricane activity can surge in an area over a few years and die off elsewhere. That, however, is where consensus ends.

Some scientists believe that human activity's contribution to global warming, which is increasing air and water temperatures worldwide, is making it easier for hurricanes to form and gain destructive force.

Other scientists believe that any increase in severe hurricanes over the past few decades would be due to natural salinity and temperature changes deep in the Atlantic—part of a natural environmental cycle that shifts back and forth every 40-60 years.

For now, climatologists are busy examining the interactions between these facts:

  • Air and water temperatures are rising worldwide. Global temperatures reach a record high in 2015.
  • Human activities such as deforestation and greenhouse gas emissions from a wide range of industrial and agricultural processes are contributing to those temperature changes at a greater rate today than in the past.
  • At the same time, hurricane activity in the Atlantic basin has been in a relative lull for many years now. Pacific typhoons (the term used for hurricanes in the Pacific basin), on the other hand, have been increasing in frequency and severity.

Learn more about the greenhouse effect and what you can do personally to help reduce global warming.

Edited by Frederic Beaudry.

Format
mla apa chicago
Your Citation
West, Larry. "What Causes Hurricanes?" ThoughtCo, Mar. 29, 2017, thoughtco.com/what-causes-hurricanes-1203855. West, Larry. (2017, March 29). What Causes Hurricanes? Retrieved from https://www.thoughtco.com/what-causes-hurricanes-1203855 West, Larry. "What Causes Hurricanes?" ThoughtCo. https://www.thoughtco.com/what-causes-hurricanes-1203855 (accessed December 12, 2017).