© Shutterstock

What is a hurricane? -

In appearance, a hurricane resembles a colossal whirlpool, a gigantic mass of revolving air. But how exactly do hurricanes and other tropical storms form, and why do they have an eye?

© Getty Images

A tropical cyclone -

The National Oceanic and Atmospheric Administration (NOAA) defines a hurricane as a type of storm called a tropical cyclone, which forms over tropical or subtropical waters.

© NL Beeld

Storm characteristics -

Hurricanes are typically marked by wind speeds over 74 mph (119 km/h), and a circular rotating motion with a clear, low pressure center: the eye.

© Getty Images

Origins of storms -

These storms are called hurricanes when they originate over the Atlantic Ocean and typhoons or tropical cyclones when they form elsewhere. However, when a storm's maximum sustained winds reach 74 mph, it is often just referred to as a hurricane.

© Shutterstock

Warm water and wind -

In order to come to life, a hurricane needs two basic ingredients, namely warm water and wind. It begins to take shape from a cluster of thunderstorms that suck up the warm, moist air and move it high into Earth's atmosphere.

© Shutterstock

How a hurricane is powered up -

This humid air mass generates a region of low pressure, which in turn creates a storm system that converts the warm air into energy, thus powering the hurricane's circular winds.

© Getty Images

Cycling of air -

The winds and storm system spin because of this cycling of the air. But momentum is also achieved by something called the Coriolis effect.

© Shutterstock

What is the Coriolis effect? -

Simply put, the Coriolis effect describes the pattern of deflection taken by objects not firmly connected to the ground as they travel long distances around Earth. It causes air and water to curve as they travel, and is responsible for many meteorological and oceanographic phenomena.

© Shutterstock

Winds of change -

For example, due to the Coriolis effect hurricanes in the Northern Hemisphere spin in a counterclockwise direction, while hurricanes in the Southern Hemisphere (known as cyclones) spin in a clockwise direction. And the greater the speed of the hurricane's rotation, the greater the strength of the Coriolis effect.

© Getty Images

What exactly is the eye of a hurricane? -

The eye of a hurricane or tropical cyclone is a region of mostly calm, clear weather in the center of the storm. This central area is of very low barometric pressure, in fact as much as 15% lower than that of the surrounding storm.

© NL Beeld

Seeing into the eye -

The eye is roughly circular in shape, typically 19–40 miles (30–65 kilometers) in diameter. It is surrounded on all sides by the storm.

© NL Beeld

What happens around the eye? -

The hurricane rotates around the eye, which itself is an area of light wind speeds and no rain.

© Shutterstock

The eyewall -

The barrier between the storm and the eye is called the eyewall. This is a ring of towering thunderstorms where the most ferocious weather and highest winds of the storm occur. It's the most devastating region of any hurricane.

© Shutterstock

The stadium effect -

An eye is always larger at the top of the storm, and smallest at the bottom of the storm. This is because the rising air in the eyewall follows isolines (contour lines) of equal angular momentum, which also slope outward with height. This sometimes gives the eye an appearance resembling a sports stadium from the air.

© Public Domain

Size matters -

Generally speaking, the more powerful the hurricane the smaller the eye tends to be.

© Getty Images

Eyewall replacement cycles -

Eyewalls can replace themselves. In meteorology, eyewall replacement cycles naturally occur in intense tropical cyclones with maximum sustained winds greater than 74 mph. In this satellite image of Cyclone Emnati, the inner wall of the storm is being replaced by a new outer wall.

© Public Domain

The cause of eye formation -

The cause of eye formation is still not fully understood. One theory is that the Coriolis effect causes wind to be deflected from the center of the storm, creating the calm eye.

© Public Domain

Role of the eyewall -

Scientists have also suggested that the eyewall itself plays a role in the formation of the eye. As a tropical storm strengthens into a hurricane, one section starts to rotate faster, forming the eyewall, which borders the eye on all sides.

© Getty Images

Air speed factor -

Most experts agree that the eye is  probably related to the conservation of angular momentum combined with centrifugal force. In science speak, conservation of angular momentum means that objects will spin faster as they move toward the center of circulation. In other words, air increases its speed as it heads toward the center of a hurricane or tropical cyclone.

© Getty Images

Eye-openers -

And while eyes are easy to spot using weather radar, the only way to investigate them properly is to fly, quite literally, into the "eye of the storm."

© Public Domain

Hurricane hunters -

Hurricane hunters are aircrews that deliberately fly into hurricanes and tropical cyclones to collect data. The Lockheed WP-3D Orion (pictured) is the NOAA's primary hurricane research platform, capable of flying directly through the hurricane's eyewall and conducting various experiments requiring flight patterns in various parts of the storm.

© Getty Images

The view from above -

The US Navy also deploy lighter, more maneuverable F9F-8P Grumman aircraft to gather photographic data by flying high above the eyes of hurricanes.

© Getty Images

Air reconnaissance -

The NOAA also use a modified Gulfstream G-IV jet as a preliminary reconnaissance vehicle to survey storm patterns. In this 2005 image, the aircraft is passing the eyewall on the backside of Hurricane Rita.

© Getty Images

Inside the eye of a hurricane -

This remarkable photograph shows the eyewall of Hurricane Katrina viewed from a highly modified P-3 Orion as it flew through the eye of one of the most destructive tropical cyclones ever to make landfall in the contiguous United States.

© Public Domain

Center of the storm -

This similar view of Katrina's eyewall includes the aircraft's antenna, used for collecting weather information.

© Public Domain

Flying into the unknown -

The P-3 Orion used by the NOAA bristles with high-tech radar and instrumentation and is uniquely designed to withstand the enormous forces of nature that pummel the fuselage. This is the view from the cockpit as a P-3 approaches daunting Hurricane Dorian in 2019.

© NL Beeld

Satellite tracking -

Satellites use infrared imagery to help meteorologists identify the areas of the greatest intensity within large storm systems, such as the areas with the most intense convection, known as overshooting cloud tops (dark orange), surrounding the eye and along the outer bands.

© Getty Images

Eyes wide shut -

As a hurricane begins to weaken, the lack of a tight spiral gyre sees the eye less well defined. In fact, as it closes the eye is often obscured by dense central cloud cover.

© Getty Images

The effects of climate change -

Hurricane Helene, which struck the Southeastern United States in late September 2024, is the latest in an increasingly catastrophic series of tropical storms to make landfall around the world. But how does climate change relate to this increase in hurricane strength?

© Getty Images

More of the same, only more destructive -

The oceans are heating up, and, as warm water is needed to fuel a hurricane and nourish its growth, it's inevitable that bigger and more powerful storms will become commonplace. And that's something scientists are keeping an increasingly concerned eye on.

Sources: (NOAA) (BBC) (Hurricane Science)

See also: What can you do to help combat climate change?

© Getty Images