As measured by the number of storms, hurricanes, major hurricanes and longevity, 2017 is among the top eight most active.
About one-sixth of an average Atlantic hurricane season is left.
The 2017 Atlantic hurricane season is now among the top eight all-time most active seasons on record, thanks to a frenetic stretch of long-lived, destructive hurricanes from mid-August through early October.
Through October 9, 15 named storms, nine hurricanes, and five 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 already a top 10 busiest season.
Through October 9, following the demise of former Hurricane Nate, 2017 was already the eighth most active Atlantic hurricane season of record, according to statistics compiled by Dr. Phil Klotzbach, 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. Each of those seasons ended up a top five active season overall, with 1933 occupying the top spot.
Roughly 16 percent of an average Atlantic season’s ACE index occurs after October 9, 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 season becomes even more compelling when comparing it to two of the most notorious recent hurricane seasons of the previous decade.
The nine-hurricane pace matches that from 2004, when four of those hurricanes hammered various parts of Florida, among other areas.
While 2017 is unlikely to touch 2005’s record 15 hurricanes through the entire season, it has already chalked up the same number of major (Category 3 or stronger) hurricanes through October 9 as that record-smashing 2005 season generated up to that point in the season.
In 2005, Dennis, Emily, Katrina, Maria (yep, same name) and Rita were at least Category 3 intensity through October 9.
A stretch of nine straight hurricanes from August 9 through October 6, in 2017 was a first in the Atlantic basin in 124 years.
Included in this stretch was catastrophic Category 4 Hurricane Harvey, followed by the long-lived saga of Hurricane Irma, then by long-lived Jose and catastrophic Hurricane Maria and finally by Nate.
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.
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 9.
Given that, 2017 may continue to climb the all-time list of notorious Atlantic hurricane seasons.
