Cape Verde Hurricanes Don't Often Strike The US; The Threat Is Usually 'Homegrown' (ANALYSIS)

C​ape Verde hurricanes are some of the Atlantic Basin's most powerful and unsettling hurricanes. While they don't often make it to the mainland U.S., they're often destructive when they do.

W​hy Cape Verde? Every hurricane season, meteorologists focus on a parade of weather disturbances known as African Easterly Waves, or tropical waves, that march westward off the coast of western Africa and into the Atlantic Ocean. According to the National Hurricane Center, about 85% of major hurricanes and about 60% of other tropical storms and hurricanes develop from these disturbances.

Sometimes one of these tropical waves wastes little time strengthening into a tropical storm and then a hurricane after moving off Africa and into the open waters of the Atlantic.

These early developers are called "Cape Verde hurricanes," after the group of islands near which they often first become tropical storms, now known as the Republic of Cabo Verde.

When and how often do they develop? Cape Verde hurricanes are usually an August or September occurrence. That's when the eastern Atlantic Ocean, not to mention much of the tropical Atlantic Basin, is most favorable for development.

T​hat said, there aren't usually many Cape Verde hurricanes. Some hurricane seasons may have as many as five. Others, such as 2022, fail to produce a single Cape Verde hurricane.

What are some examples? The most recent Cape Verde hurricanes were in 2021, when both Larry and Sam intensified quickly between Africa and the Lesser Antilles.

Another recent example was 2019's Hurricane Lorenzo. Lorenzo not only developed south of the Republic of Cabo Verde, but also exploded into the strongest hurricane on record in the eastern Atlantic Ocean.

How often are they a U.S. threat? Weather.com analyzed 217 hurricane tracks from 1995 through 2022 to find out just how much of a threat to the U.S. these Cape Verde hurricanes have been.

That period was selected because hurricane seasons have generally been more active since 1995.

The analysis revealed these hurricanes don't often reach the mainland U.S., but when they do, they tend to be destructive.

Of those 217 hurricanes, 54 either made landfall or brushed very close to the mainland U.S. to produce some direct impacts. That's an average of about two U.S. hurricanes per season since the mid-1990s.

But the analysis found that only eight out of 54 hurricanes that reached the U.S. were of the Cape Verde variety.

Why do so few Cape Verde hurricanes reach the U.S.? Just because a hurricane develops quickly in the eastern Atlantic Ocean doesn't mean it will ultimately threaten the mainland U.S.

There are several reasons for this beyond the relatively few number of them each year mentioned earlier.

Cape Verde hurricanes have thousands of miles of ocean to cover to make it to the U.S. A lot of things often go awry along the way.

They can be carried farther north into the central Atlantic Ocean if the Bermuda high is weaker or less expansive than normal. These recurving storms then curl around the weaker high well off the U.S. East Coast.

Surges of hot air from the Sahara Desert known as Saharan Air Layers move off the African coast every 3 to 5 days from late spring through early fall.

Wind shear is another factor that doesn't allow development in the eastern Atlantic Ocean early in the season. These differing winds with height can rip apart a system trying to become a tropical storm.

All of this means that Cape Verde hurricanes are usually confined to that narrower window of the hurricane season, typically either August or September.

Those that made it were very impactful. While Cape Verde hurricanes are few and make up a small fraction of U.S. hurricane landfalls, those that have made the entire voyage were almost always very destructive.

September 2018's Hurricane Florence was the last Cape Verde hurricane to hit the U.S. Despite downshifting its winds before landfall, its slow crawl over the Carolinas triggered catastrophic flooding.

Others included Irma (2017), Ike (2008), Ivan (2004), Frances (2004), Isabel (2003), Georges (1998) and Bertha (1996).

All but one of these - Bertha in 1996 - were so damaging their names were retired from future use.

In these cases, there was not enough dry air or wind shear to put a lid on their intensification, and expansive, strong high pressure to their north ensured they would be steered to the U.S.

U​.S. threat is usually "homegrown." The bigger hurricane threat for the U.S. usually comes from storms that develop much closer.

As the map below shows, of the 54 U.S. impacting hurricanes from 1995 through 2022, only 10 of them first became hurricanes between the Lesser Antilles and Africa.

The large majority of them first became hurricanes in the Caribbean Sea, Gulf of Mexico or near the Southeast coast.

One reason for this more homegrown hurricane threat is simple geography. The closer to the U.S. it becomes a hurricane, the better chance of a U.S. hurricane landfall.

For instance, a Gulf of Mexico hurricane has nowhere else to go except Mexico or the U.S. if it doesn't fizzle first.

But sometimes the tropical wave encounters a hostile environment of dry air and wind shear elsewhere in the Atlantic, only to find a much more hospitable environment closer to the U.S.

Deep, warm water is typically most plentiful in the Caribbean Sea and Gulf of Mexico, so development in this part of the tropics isn't simply limited to August and September.

Wind shear ripped apart Tropical Storm Harvey in the eastern Caribbean Sea only for it to roar back as Cat. 4 Hurricane Harvey in the Gulf. It then slammed and flooded out parts of coastal Texas.

Every hurricane should be taken seriously, particularly those in the Caribbean Sea, Gulf of Mexico, or off the Southeast coast.

But much more often than not, Cape Verde hurricanes – even stronger ones – have to clear some atmospheric hurdles before they become a U.S. threat.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. His lifelong love of meteorology began with a close encounter with a tornado as a child in Wisconsin. He studied physics at the University of Wisconsin-Madison, then completed his Master's degree working with dual-polarization radar and lightning data at Colorado State University. Extreme and bizarre weather are his favorite topics. Reach out to him on X (formerly Twitter), Threads and Facebook.

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