In the midst of the 2020 Atlantic hurricane season, Pete Dailey, vice president at RMS compares and contrasts 2005, perhaps the most memorable Atlantic season in recorded history, to 2020.
2020 has already proven to be “hyper-active”. Arthur and Bertha formed before the official Atlantic hurricane season kicked off on 1 June, 2020 and by 15 September, 2020, roughly the season’s midpoint, 21 tropical cyclones have developed, 20 of them named, nearly double the average for an entire season of about eleven.
Every named storm this year has been born — what meteorologists refer to as its “genesis” — prior to its 2005 counterpart. Tropical Storm Vicky formed nearly three weeks prior to Hurricane Vince that formed on 5 October, 2005.
The second half of the season has yet to play out, but if conditions persist, the 2005 record of 28 named storms in a single season could be broken this year, though storms are only relevant to the insurance industry if they develop damaging winds and make an impact on insured exposure.
Overlaying storm intensity onto the same chart (graphic 2), again for 2005 and 2020, shows that only seven of the 21 tropical cyclones at the season midpoint (Hanna, Isaias, Laura, Marco, Nana, Paulette, and Sally) reached hurricane strength. Four only achieved short-lived CAT1 status — though Laura made landfall as a CAT4 hurricane and produced widespread loss owing to both wind and flooding along the Gulf Coast. CAT1 hurricanes can be destructive, but pale in comparison to the disaster potential of a major hurricane (CAT3 and above).
By this point in the 2005 season, nine cyclones had reached hurricane strength, four were major hurricanes.
“Storm frequency matters, but storm intensity matters more”
Dennis reached CAT4 status; Emily reached rare CAT5 status with winds exceeding 160 miles per hour! Hurricane Dennis set the record for the strongest hurricane to form before August, a record broken just a week later by Emily.
At this point in mid-September, nobody could have predicted what was in store for the remainder of 2005 culminating in a record number of named storms, number of storms prior to August, number of hurricanes, major hurricanes, CAT5 hurricanes, and number of days with an active storm in the basin.
That remarkable season included Hurricane Katrina, the most devastating hurricane landfall on record, which itself broke a number of additional records that year.
What matters most: wind damage potential
Storm frequency matters, but storm intensity matters more. At the end of this year we’ll need to consider both the number of storms and their intensities to measure 2020 against 2005.
The Accumulated Cyclone Energy (ACE) index provides an integrated metric, combining frequency and intensity as a proxy for the total wind energy generated by storms over the course of an entire season. ACE approximates the wind energy of each tropical system for every six hours of its life cycle.
Seasonal ACE is the sum of ACE for each individual storm — a useful metric for risk managers, accounting for the number, intensity, and duration of storms.
The chart below shows the development of ACE over the 2005 season, and a seasonal value of about 250 — 2.5x the average seasonal ACE of 105. The large jumps in 2005 corresponds to the intensifying individual storms like Katrina, Rita, and Wilma. But even weaker storms contributed to ACE in 2005.
As of September 15, 2005, the ACE index had reached a value of 145, which is 138% of the wind energy expected in an entire season.
So far this year, the ACE index value is at 64, roughly equal to the long-term average (as indicated by the solid black line). The key difference—despite the rapid pace of genesis in 2020 — many tropical cyclones this season have been weak and short-lived, which detracts from the total ACE value.
“We’ll have to wait until later this year to assess the financial impacts of the 2020 season”
In contrast at this point in 2005, three fewer tropical cyclones had developed, but they strengthened and persisted, leading to an ACE value over double that of 2020.
ACE is a useful metric because it applies directly to damage potential as it accumulates each storm’s maximum winds over time. But there’s still an element of damage potential missing in ACE, namely the size of the wind footprint.
To take storm size into account, the TIKE index was developed. TIKE stands for Total Integrated Kinetic Energy and is similar to ACE, but incorporates the wind radius of each storm. It accumulates the total area over which damaging wind energy is produced for the entirety of each storm’s life cycle and then summed up for the entirety of each storm season.
TIKE provides us with a useful metric to compare overall damage potential from one season to the next.
Because accurate and dependable measurements of storm radii have only been available for the past couple of decades, we have a more limited historical record of TIKE.
We’ve calculated TIKE over the past 18 seasons, with the results shown in the chart below.
Note, the average seasonal TIKE value over this period is about 8.0 (8,000 terajoules), and the average value as of September 15 is about 3.8 (3,800 terajoules).
At this point in a typical season — nearing the peak, TIKE has accumulated about half of its season total.
By the end of 2005, TIKE had reached a value of 13.0, second only to the 2012 season in which Hurricane Sandy’s size, strength, and duration spiked the TIKE value late in that season. In 2005, not only was the wind damage potential extremely high, but much of that potential was realized in the form of landfalling hurricanes producing devastating damage in the Caribbean and US.
As of 15 September this year, the TIKE value has reached 3.6, slightly less than the long-term average of 3.8. At this point in September, many seasons over the last 18 years have recorded higher TIKE values, such as 2005 which had already reached a value of 6.5—70 percent higher than the long-term average and the TIKE value this season. So, from the perspective of integrated wind damage potential, 2005 eclipses the integrated wind energy so far this year and almost every year since 2002. The exceptions are 2004, another active season with many strong long-lasting hurricanes, and 2008, when by 15 September, TIKE had spiked due to long-lasting and strong hurricanes like Bertha and Ike.
When we look back at the 2020 hurricane season a few months from now, we will question whether reasonable comparisons to 2005 can be made. On its face, 2020 appears to be off to an unprecedented start with every named storm in 2020 developed prior to its 2005 counterpart. Dig a bit deeper and consider metrics important to quantifying damage and loss—namely storm intensity, duration, and size— we quickly realize that the level of wind energy and potential damage generated in 2005 sets a very high bar that will be difficult to surpass.
We’ll have to wait until later this year to assess the financial impacts of the 2020 season overall and make comparisons to past seasons like 2005.