Tropical Wave Could Be Next Tropical Depression

Historically speaking, September is the most active month of the Atlantic Hurricane Season. Recent years have been no different.

Busy, lately: September 2024 brought the first of the two devastating hurricane strikes of the season for the Southeast: Hurricane Helene. Helene caused massive flooding in the Appalachians and killed at least 250 people.

At least six September storms have formed each of the past seven years in a row. And the past eight Septembers have each delivered 3 or 4 hurricanes. That included a record 10 September storms in the frenetic 2020 hurricane season.

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What ultimately matters is how many of these storms strike land.

Once again, September tops all other months for U.S. hurricane landfalls since the mid-19th century, per NOAA-HRD.

The list of recent September landfalls is a virtual who's who of U.S. hurricanes this century, including Ian, Ike, Irma, Ivan and Maria.

Visualizing the peak: When examining a graph of storms and hurricanes, September sticks out as the peak of the mountain that is hurricane season, as you can see below.

When averaged over the historical record, the number of storms and hurricanes has usually been highest around the second week of September.

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What's usual: From 1991 through 2020, an average of four to five storms formed each September, according to data from the National Hurricane Center.

Of those September storms, two to three became hurricanes, with one reaching at least Category 3 or stronger.

Using a metric called the ACE index, which doesn't simply count storms but also factors how long-lasting and intense they are, September usually accounts for 45% of a total season's activity, according to data compiled by Colorado State University tropical scientist Phil Klotzbach.

The "major" hurricane generator: No other month churns out as many intense Atlantic hurricanes as September.

According to data from NOAA's Hurricane Research Division (HRD), just under half of all hurricanes of at least Category 3 intensity since the mid-19th century have happened in September (166, to be exact). That's more than August (94) and October (68) combined.

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Why it's so busy: Put simply, the favorable conditions for hurricane formation overlap best in September over the largest area of the Atlantic Ocean, as you can see in the map below.

September has the ideal overlap of low wind shear and ocean temperatures reaching their warmest. It also has less widespread surges of dry, thunderstorm-suppressing air from the Sahara than earlier in the hurricane season. It's in this favorable environment that a parade of disturbances known as tropical waves march westward off west Africa, occasionally the seeds of September hurricane development.

Not every September: A few years have had much quieter Septembers.

Eleven years ago, during a season that generated just eight total storms (2014), September only saw two storms form, neither of which struck the U.S.

And September 1997's only storm, Erika, avoided the Leeward Islands, then became the season's only Category 3 hurricane well east of Bermuda.

Be ready every September, regardless: Statistics and history illustrate the importance of having your hurricane plan ready to go, especially in September.

While some September storms develop in the eastern Atlantic Ocean and may offer many days warning, others can develop quickly and much closer to the U.S.