Accumulated Cyclone Energy ...is the 2020 Atlantic Hurricane Season really as active as some say?

 

Accumulated Cyclone Energy,  ACE measures the total wind energy realized over the entire life cycle of all storms in a tropical season. ACE is an index that combines the numbers of systems, how long they existed and how intense they became.  The ACE Index is intended to provide better insight into a seasons overall intensity than simply counting the number of storms. On average 76% of a seasons total ACE happens after August, 28. Historically, only two named storms form on average by early August. Based on this, our 2020 season is basically just getting started.

ACE comes to be especially important when trying to compare different hurricane seasons in an effort to show the differences in power used during the seasons. A hurricane season could have an above-average number of storms, but if they were all weak, the season could still score lower than a season that had fewer storms overall but also some major hurricanes.

A paper authored by Carl Drews asserts “The results show that the recent increase in Atlantic hurricane activity is primarily due to an increase in the number of storms per season, with increased hurricane intensity playing a secondary role.”

NOAA uses the ACE index of a season to classify the season into one of four categories. The categories break down as:  below average, near average, above average, and extremely active season and are based on the ACE index, number of tropical storms, hurricanes and major hurricanes over the 30 years between 1981 and 2010.

Atlantic basin

Category	ACE Index	Tropical storms
Average	105.6	12.1
Extremely active	Above 152.5	Not defined
Above-normal	Above 111	13 or more
Near-normal	66-111	10-13

Chart source Wikipedia

 

This year most weather outlets are forecasting the (Atlantic) ACE value to be somewhere between 150 and 200. Numbers that high would qualify 2020 as a hyperactive season.

 2005 and 1995 were very active years in the Tropical Atlantic. 2005 saw 28 named (including an unnamed subtropical storm added during post season analysis). Of the named storms, 15 were hurricanes with 8 of those being major, 4 of those major hurricanes obtained category 5 status: Emily, Katrina, Rita, and Wilma. The 2005 Atlantic hurricane season was the most active Atlantic hurricane season on record going back to 1851. But we have to keep in mind, that before the satellite era, tropical cyclones could have escaped notice. Seven of the named storms made landfall in the United States.

The 1995 Atlantic hurricane season was another hyperactive season with 19 named storms, 11 hurricanes and five major hurricanes: Felix, Luis, Marilyn, Opal and Roxanne.  One thing that really makes 1995 standout is the fact there were 5 named storms in the Atlantic Basin at the same time, Humberto, Iris, Jerry, Karen and Luis.

Based on ACE the 1933 hurricane season was the most intense season in the historic record going back to 1851.     1933 had a total ACE in the North Atlantic of 258.6.  The year in 2nd place based on ACE is 2005 with an ACE of 245.3. 

When looking at the number of named storms, 1933 was the 2^nd most active on record. It is estimated to have produced 20 named storms.  As I said before, without Satellite observation, if tropical cyclones stayed out to sea away from populated areas or shipping lanes, especially if they were short duration and relatively weak, could’ve remained undetected. Of the 20 storms during the season, 11 attained hurricane status. 6 of those were major hurricanes. This broke the record for most known named storms set back in 1887. Out of the 6 major hurricanes, 5 of them made landfall on the United States. Two of those major hurricanes made landfall one day apart. The 1933 Hurricane Season was notable in two respects. First, the 21 tropical disturbances recorded that year was a record in the Atlantic (eclipsed in 2005), and second, the majority of storms moved farther west than is usual. Seven of these made landfall between Corpus Christi and Tampico, Mexico

So, the total number of storms isn’t really telling the whole story about 2020. While we’re having a record setting pace for named storms; the ACE is lagging quite a bit.  So far, the total amount of energy produced in the North Atlantic has been 45.1, the vast majority of which consist of Isaias (9.19) and Laura (12.75), the rest is comprised by the rest of the pack, showing how weak and short lived those tropical cyclones were. We still in the peak of the Atlantic season with still half of the season to go. So, there is still plenty of time for total ACE to climb. The potential of more tropical cyclones impacting the Mid-Atlantic and Northeast are still quite high, based on the climatological average.   Just because most of the storms this season have been weak and short lived, doesn’t mean this will be the case for September and October. I don’t believe our region is done with tropical cyclones this season….so keep your guard up…

 

Source Colorado State University