For a large portion of the world, the summertime brings more than just warm temperatures—every year is a looming threat of potential hurricanes.

This form of extreme weather was estimated to impact nearly 800 million people in 2019.

Historic storms like Hurricane Katrina, Hurricane Irma, and Hurricane Maria have ravaged cities, destroyed infrastructure, and reshaped the future of coastal communities. Flooding has left long-term impacts, at times forcing localities to relocate entirely. With projections that hurricane formations are only becoming more powerful and more frequent, here’s everything you need to know about hurricane season.

How are hurricanes classified?

Hurricanes, or intense tropical cyclones, are defined as “a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has a closed low-level [pressure] circulation,” according to the National Hurricane Center. Other parts of the world refer to hurricanes as typhoons or cyclones.

Depending on wind speed, these tropical cyclones fall into one of four categories:

tropical depression (less than 38 mph), tropical storm (39-73 mph), hurricanes (74 mph or higher), and major hurricanes (111 mph and higher).

For the most intense hurricanes, scientists use the Saffir-Simpson wind scale, which designates categories 1-5 for hurricanes based on wind speed and projected damage.

Category 1 hurricanes have winds between 74 and 95 miles per hour—some damage will occur including damage to power lines that could impact access to electricity for a number of days. Category 2 hurricanes are between 96 and 110 miles per hour with extensive damage leading to near-total power loss that could last upwards of several weeks.

Category 3 hurricanes can lead to “devastating” damage with wind speeds between 111 and 129 mph. Category 4 brings winds 130-156 miles per hour and can lead to power outages for months. The most destructive, Category 5, involves wind speeds more than 157 mph and leaving areas affected uninhabitable for several months.

When is hurricane season and where does it hit?

Since hurricanes and tropical cyclones form over different bodies of water, the world is split up into seven different hurricane basins. The United States is impacted by both the North Atlantic and Eastern Pacific basins.

Officially, the Atlantic hurricane season begins June 1 and ends Nov. 30. The territories in this basin include the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. The Pacific season begins on May 15 and ends Nov. 30, stretching from Mexico to Central America.

Is hurricane damage getting worse?

Through analysis of previous storm patterns, scientists have identified how things like higher sea levels and hotter temperatures are impacting hurricanes.

Warmer ocean water and warmer atmospheric temperatures have led to greater wind speeds, higher rainfall, and increased flooding. One estimate found the effects of climate change increased the likelihood of extreme rainfall during Hurricane Harvey in 2017 three times more likely, according to the BBC.

While there is limited evidence that hurricanes are actually increasing in frequency, extreme damage from powerful hurricanes is becoming more common in the United States. Increased population growth along the coasts and raised sea levels shows greater costs and destruction compared to 100 years ago.

In 2017, Houston saw massive flooding after Hurricane Harvey. Analyses show that increased growth and development, in lieu of a proper zoning code, led to the reduction of green areas that previously prompted water absorption and runoff. This, in combination with increased rainfall, brewed the perfect storm for a disaster that claimed the lives of dozens and cost $125 billion in damages.

Experts point toward an overhaul of current procedures, zoning, and infrastructure to mitigate any future devastation from hurricane severity. Patterns and predictions call on the need for wetland preservation, building elevation, improving awareness initiatives, and reinvestment in planning for climate risks.

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