Is 2021 a Destructive Hurricane Season ?

 

Hurricane Ida, August 2021  (Source: WUSA9)

With 20 tropical storms, of which seven became hurricanes, including four major ones, 2021 has been an active Atlantic hurricane season.  It’s also been a costly hurricane season with several very destructive storms that made landfall in the United States, including Henri, Ida and Nicolas.  NOAA estimates that Hurricane Ida caused $60 billion in damages, making it one of the costliest natural disasters in U.S. history.

Since the hurricane season continues through the end of November, there is a lot of time left for another storm to develop in the Atlantic Ocean Basin (that includes the Gulf of Mexico and Caribbean Sea).  Although the last six weeks of the season, typically gets much quieter, late October and November can still be quite active.  For example, November 2020 had three named storms, including two Category 4 hurricanes. 

Even if 2021 doesn’t see any more named storms, this season will finish among the Top 5 most active Atlantic hurricane seasons in terms of total number of named storms.  However, the overall number of tropical storms and hurricanes in a given season isn’t always a reliable metric of how busy a season is.  That’s because there can be a high number of weaker, short-lived systems that pad the total number of named storms. 

Another measure of how active a hurricane season is that meteorologists look at is the “ACE Index” which stands for “Accumulated Cyclone Energy.”  This index includes factors such as overall storm intensity, how long a hurricane remains a major Category 3 or higher storm, and overall storm duration. 

Although 2020 set a record season total with 30 named tropical storms, its final ACE Index ranking for the season did not put it among the Top 10 most active Atlantic hurricane seasons.  That’s because there were a significant number of weaker, short-lived systems, similar to this season.  Looking solely at the ACE Index, five of the 10 busiest Atlantic hurricane seasons have occurred since 1995.  That makes sense since the tropical Atlantic has seen an uptick in activity since 1995 compared to the previous 25-year period.

While the 2005 season set an Atlantic record with 15 hurricanes, including four Category 5 hurricanes, it finished narrowly behind the 1933 season for most active season based on the ACE Index.  Besides 2005, other recent seasons that finished among the Top 10 Atlantic hurricane seasons based on the ACE Index are 2004 and 2017.  What those seasons all had in common is how at least one Category 5 hurricane developed.  However, there have been other seasons with a high ACE Index that didn’t have a Category 5 hurricane, such as 1995.  2021 would need several more named storms to approach the list of Top 10 seasons on the ACE Index.