How does a storm become a hurricane? The dangers in 5 categories

Severe weather can strike any part of the world, but each year the Atlantic hurricane season brings heavy rain, strong winds, storm surges and sometimes catastrophic devastation to places from the Caribbean islands and Central America to the United States and Canada.

Meteorologists at the Miami-based National Hurricane Center monitor storms from their formation to their dissipation. This year, the 2024 season was expected to be extremely active, producing the earliest Category 5 Atlantic hurricane on record.

But how do these hurricanes form and what do the categories mean? A look at the facts:

What causes a hurricane?

According to the National Oceanic and Atmospheric Administration, hurricanes often begin as tropical waves that combine with warm ocean water. They can also be fueled by thunderstorms. The weather system is moving westward as warm ocean air rises into it, creating a low pressure area underneath, NOAA said. Air rises and cools, forming clouds and thunderstorms.

Hurricanes have maximum sustained winds – the highest average wind speed in a minute at a given time – of 74 mph (120 km/h) or more. When a tropical cyclone has maximum sustained wind speeds between 39 and 73 mph (63 km/h to 120 km/h), it is called a tropical storm. If the maximum sustained wind speed is less than 60 km/h, it is called a tropical depression.

Hurricanes typically occur during hurricane season, which occurs in the Atlantic basin from June 1 to November 30 each year.

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What different hurricane categories are there?

The Saffir-Simpson Hurricane Wind Scale rates hurricanes on a scale of one to five. Category 1 hurricanes reach speeds of 74 to 95 miles per hour and can bring very dangerous winds that can damage even sturdy homes. Category 1 is the weakest hurricane, and storms strengthen up the scale from there.

If a hurricane is Category 3 or higher, it is considered a major hurricane. Category 3 hurricanes begin with maximum sustained winds of 111 mph (180 km/h).

How severe is a Category 5 hurricane?

Catastrophic. A Category 5 hurricane destroys homes, knocks out power to large areas, and isolates communities due to downed trees and downed utility poles. It can also cause severe damage to infrastructure such as roads, bridges and dams. A Category 5 hurricane can make large areas uninhabitable for weeks or longer.

What destruction do hurricanes cause?

The damage caused by a hurricane depends on its strength and where it makes landfall. Even a relatively weak hurricane can cause extensive damage and many deaths if it hits a vulnerable community or damages a key piece of infrastructure. A moderate hurricane like Hurricane Jeanne in Florida in 2004 will cause devastating damage to homes, infrastructure and the power grid. Deaths are also often attributed to flooding, accidents, injuries, and other disruptions caused by the storm.

What was the deadliest hurricane in the US?

The 1900 Galveston hurricane in Texas is the deadliest natural disaster in U.S. history, according to NOAA and other agencies. The storm killed at least 8,000 people, destroyed thousands of buildings and left hundreds of millions of dollars in damage by today's standards. Other exceptionally deadly hurricanes in recent history include Hurricane Maria, which killed more than 3,000 people in 2017, and Hurricane Katrina, which killed more than 1,300 people in 2005.