Hellish September for hurricanes finally comes to a close

Records fall, even with a quarter of storm season to come

Farewell, September. Don’t let the door hit you on the way out.

By some measurements, September marked the single worst month for Atlantic hurricanes ever recorded.

In a statistic known as Accumulated Cyclone Energy (ACE), Hurricanes Irma, Katia, Jose, Lee and Maria generated the largest amount of energy for any month on record, said Colorado State University meteorologist Phil Klotzbach.

ACE is calculated by adding each tropical storm or hurricane’s wind speed through its life cycle. Longlived, intense hurricanes have a high count (Irma’s ACE measured 67.5), while short-lived, weak tropical storms have a lower values (Katia came in at 6.1), according to Weather.com.

Irma and Maria soared to Category 5 strength, the top of the Saffir-Simpson scale of hurricane intensity. Irma’s landfall on Barbuda and Maria’s landfall on Dominica makes 2017 only the second season on record to feature two hurricanes of Category 5 strength.

The Atlantic Basin, which includes the Gulf of Mexico and the Caribbean Sea, also generated 35 “hurricane days” in September, the most ever recorded in the Atlantic, Klotzbach said.

A “hurricane day” is tallied each time a hurricane spins for 24 hours somewhere in the Atlantic, meaning there can be multiple “hurricane days” in a single 24-hour period.

These statistics don’t necessarily gauge a hurricane season’s impact on people and property, however.

Irma killed 87 people in the U.S. and its territories; the U.S. death toll from Maria now stands at 24, all in Puerto Rico.

September wrought catastrophic damage to the southeastern U.S. and Puerto Rico, in addition to several other Caribbean islands, primarily because of Irma and Maria. When the destruction from Harvey in August is lumped in, this year’s crop of devastating storms could make it the costliest hurricane season ever for the USA.

“There is no question that this is already going to be one of the costliest Atlantic hurricane seasons on record — and we’re only in September,” said meteorologist Steve Bowen of global reinsurance firm Aon Benfield.

Hurricane season isn’t over, unfortunately. Based on historical averages, we still have about 25% of the season left. On average, 1.5 hurricanes form each year in the Atlantic in October and November, the NOAA said.

As Maria and Lee race out to sea away from the United States, the National Hurricane Center is watching a small area of disturbed weather spinning near Cuba. The disturbance has a 40% chance of becoming a named storm over the next five days.

In October, forecasters usually look closer to home in the Caribbean, Gulf of Mexico or Atlantic Ocean for developing storms and hurricanes. The long-lived hurricanes that form near Africa and move slowly across the ocean, like Irma and Maria, are not as common this time of year.