2017 Atlantic Hurricane Season Now Seventh Most Active in History

At a Glance

• As measured by the number of storms, hurricanes, major hurricanes and longevity, 2017 is among the top seven most active.
• About one-sixth of an average Atlantic hurricane season is left.

The 2017 Atlantic hurricane season continues to climb the ranks of the all-time most active seasons on record, thanks to a frenetic stretch of long-lived, destructive hurricanes from mid-August through early October.

(MORE: Hurricane Central)

Through Oct. 14, 15 named storms, 10 hurricanes, and six major (Category 3 or stronger) hurricanes had formed in the 2017 Atlantic hurricane season.

By one measure of activity called the ACE (Accumulated Cyclone Energy) index, which adds each tropical storm or hurricane's wind speed through its life cycle, the 2017 season is easily a top 10 busiest season.

Through Oct. 14, this year is already the seventh most active Atlantic hurricane season of record, according to statistics compiled by Dr. Phil Klotzbach a Colorado State University tropical meteorologist.

Long-lived, intense hurricanes have a high ACE index, while short-lived, weak tropical storms have a low value. The ACE of a season is the sum of the ACE for each storm and takes into account the number, strength and duration of all the tropical storms and hurricanes in the season. 

According to a National Hurricane Center report, only 1933 and 2004 had a faster ACE pace through the end of September than 2017. As the graph above shows, each of those seasons ended up a top five active season overall, with 1933 occupying the top spot.

Roughly 15 percent of an average Atlantic season's ACE index occurs after October 15, according to Klotzbach's climatology.

Just an average amount of ACE the rest of this season would place 2017 close to the top five most active seasons in the satellite era. 

How This Compares to 2004 and 2005

This year has had the same number of named storms (15) as 2004, one more hurricane than that year (10), and an equal number of major (Category 3 or stronger) hurricanes (6).

While 2017 is unlikely to touch 2005's record 15 hurricanes through the entire season, it has chalked up almost as many major (Category 3 or stronger) hurricanes as that record-smashing 2005 season which had seven.

(MORE: Four Hurricanes Made a U.S. Landfall in 2017, a First in 12 Years)

The 30-year average number of hurricanes for an entire Atlantic season is six. The entire 2016 season generated a total of seven hurricanes, needing Hurricane Otto over Thanksgiving to get to that season total. 

(MORE: How a Borderline La Niña Could Impact the Rest of the 2017 Hurricane Season)

In all, September 2017 was the single most active month for Atlantic tropical cyclones on record, topping the previous record from September 2004. 

According to the National Hurricane Center, an average hurricane season typically sees another two named storms, one of which attains hurricane intensity, after October 15.

Given that, 2017 may continue to climb the all-time list of notorious Atlantic hurricane seasons.

Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.