The Comparison of the 2020 and 2005 Seasons Raises the Question:  How Do You Quantify Tropical Activity?

As we have gone deeper into the 2020 Atlantic Hurricane Season, there has been more and more discussion about how the season stacks up against very active seasons of the past, namely the 2005 season.  In terms of the number of named storms and how quickly the list of storm names has been used up, you could say that the 2020 season is a record breaker.  However, if you compare the quality of the storms that have developed this year versus those in 2005, there is no comparison, the 2005 season is head and shoulders above this year.  The comparison does raise the question:  What is the best way to quantify tropical activity?

Looking at the numbers from this season:  18 depressions, 17 named storms, 4 hurricanes, and one major hurricane.  The one major hurricane, Laura, is currently the strongest storm in the Western Hemisphere this year with maximum sustained winds of 150 mph, and a minimum central pressure of 937 millibars, or 27.67 inches.  

Meanwhile, the 2005 season already had two Category Five Hurricanes by the first week of September: Emily, and Katrina.  Another was also a Category Four storm (Dennis).  The season would end up exhausting the alphabet of traditional storm names, and use up the Greek Alphabet, which had never happened before.  The 2020 season is more than likely to do that as well, but many of the storms this season have not really been that strong at all.  Many were just mild to moderate tropical storms.

Those that did manage to become hurricanes, didn’t become as intense.  Even Laura, as strong as it was, and causing all the damage and destruction that it did in Southwestern Louisiana, still pales in comparison to the intensity that Emily, Katrina, Rita, and Wilma reached.  By September 8, 2005, there had already been four major hurricanes, and ultimately, there were seven.  The 1969 Atlantic season had 18 named storms and 12 hurricanes with five of them becoming major hurricanes.

The 1995 season, the year that kicked off the current active cycle that we have been dealing with in the Atlantic, had 21 depressions, 19 named storms, 11 hurricanes, and five major hurricanes.  However, many of those major hurricanes:  Felix, Humberto, Luis, and Marilyn, stayed away from the United States.  Luis and Marilyn did cause considered damage in the Lesser Antilles.  The 2005 season had a number of deadly and devastating hurricanes such as Dennis, Emily, Katrina, Rita, Stan, and Wilma.  Katrina alone caused over $80 billion in damage.

So, how should we measure an Atlantic Hurricane Season?  Should it be measured in terms of the numbers of depressions, named storms, hurricanes, and major hurricanes?  Should it be quantified in respect to how much energy they generate or how long they last (ACE)?  Or perhaps, they should be analyzed in terms of the number of landfalling hurricanes, and the amount of damage and deaths caused?

Let’s take a look at several below average seasons:  1935, 1938, and 1992.  All three years ended up being below the historical averages in terms of the number of named storms and hurricanes.  All three seasons had single digit named storms, and averaged a little more than four hurricanes.  However, each ended up with a memorable storm that was powerful, devastating, and deadly.  

The 1935 season had the Labor Day Hurricane that swept through the Florida Keys, and set the standard for hurricane intensity for decades.  The 1938 season had the Long Island Express, a major hurricane that rapidly moved up the Eastern Seaboard like no other such storm has done since.  And then, there was Hurricane Andrew in 1992.  Andrew was a storm that may have served as a harbinger of all the powerful storms we have seen during this current active period.

Following a path close to that of the 1935 Labor Day Hurricane, Andrew grew to be a Category Four Hurricane when it came ashore near Homestead in South Florida.  Ten years later, the storm would be reclassified as a Category Five Hurricane.  More importantly, Andrew was a storm that shattered previous records for cost of damage.  The hurricane, which forced Florida, and particularly South Florida to re-evaluate how strong building codes were, ended up being responsible for some $27 billion in damage.

I always look at these three seasons as great examples of how numbers of depressions, storms, hurricanes, and major hurricanes in a particular season, or the collective energy of all the storms in that season don’t really matter as much.  There only really needs to be one storm to make a season.  A storm that makes landfall and causes significant damage and casualties.  The 1995 season is another good example since it is a year with a lot of activity, but not much in the way of damage and devastation to land.

Another issue to keep in mind is that the Atlantic basin is just reaching its statistical peak in terms of activity.  September 10th is historically the peak of the season.  However, when you read social media posts, you get the impression sometimes that the season is over as early as July or August.  The past two seasons have been classic examples.  A year ago, there were 5 depressions and 4 named storms for the season as of late August.

Then came the monster that was Hurricane Dorian.  It was a Category Five beast that devastated the Northern Bahamas.  Dorian ended up being the most powerful storm to ever affect that part of the world.  The storm also kicked off a period with 9 named storms, 4 hurricanes, 3 major hurricanes, and 2 Category Five Hurricanes.  It was the kind of activity that exceeded those of the 1935, 1938, and 1992 seasons in their entirety.

The moral of the story is, there is still a long way to go before the 2020 Atlantic Hurricane season winds up at the end of November.  The active period usually goes to about October 10th, and there is often a second peak towards the end of October.  There can even be storms in the month of December.  Storms such as Hurricane Opal (1995), Superstorm Sandy (2012), Hurricane Lenny (1999), Hurricane Kate (1985), and Hurricanes Michelle and Olga (2001) emerged during the latter portions of the Atlantic season.