Storm Activity in the Atlantic Basin

Most Americans have a relatively firm grasp on how far a mile is. You know how long it would take to walk, bike or drive and how tired you would be after running one. Despite that understanding, it's difficult to use that as a baseline for understanding the size of a major tropical storm. When you say 'take a mile and multiple it by a few hundred', we lose our comprehending. Perhaps a better way to think about the size of a massive hurricane is to think in relative terms, so imagine for a moment that you are planning a road trip. Perhaps you are legging it from Boston to Baltimore, Chicago to Minneapolis or San Francisco to Los Angeles. If these distances seem far, it's because they are.

Your trip will take, depending on traffic and how heavy your foot is, around 6 hours. In another universe, you just drove the wall to wall width of a category 5 major hurricane.

While the size of these storms are difficult to fathom, possibly even more perplexing is what lies at the heart of the storm. Surrounded by an unrelenting mayhem of torrential rain and fierce winds lies a calm oasis. A half-time of sorts, this part of the storm lets the victims in its path breathe for a moment before continuing the latter half of its assault.

Storms vary in just about every trait — size, shape, path, winds, pressure and duration to name several. Consensus in the scientific community allows us to know that as the environment is impacted by human activity, the severity of storms increases. Human-accelerated climate change warms the oceans and warmer oceans act as a fuel source for storms to gain strength. Something I'd like to learn more about is how human activity impacts the frequency of these storms. Even a slight change in frequency or severity of such behemoth weather events could have widespread rippling effects.

To look at changes in frequency over time, it's best to look at changes on a time period longer than one hurricane season. While single seasons and even single storms can say a lot about underlying conditions, I am most interested in how things are changing over time.

This chart is a mess. There isn't much to deduce at first glance, except that the year-to-year variability is enormous. If you squint, you'll see the gold and red bars poking out over the top more often than the blue ones. It's worth mentioning that 2020 was the most active season in history and 2024 produced 11 hurricanes — the most in any season since 2005. To better dissect this view, let's look at how that activity distributes across the months of the year.

We can more clearly see some trends here. The first thing you may notice is that there is generally more variability between years as time progresses. The second is a gradual but consistent increase in storms over time. This is evident on an annual and a monthly basis. Here is a more concise look at the changes we can observe over time:

Pick any measure you like and adverse changes are present. Over time, storms are starting earlier and happening more often. In most measures, there seems to be a larger change from the 90's to 00's than any other decade. This makes sense, as we know that 2005 was one of (maybe the, depending on how you measure) worst hurricane seasons ever.

What About Severity?

Similarly, I'm interested in changes over time, but can also appreciate the immediacy and grandeur of changes in severity of individual storms. Let's look at both.

First thing first, what does it mean for a storm to be more severe? A commonly used metric by storm trackers is Accumulated Cyclone Energy (ACE). This calculation is a measure of a storm's sustained winds for the duration of its life and can be combined with the ACE of other storms to give a view of their combined strength.

Here is a chart showing the combined ACE of storms in each year from 1980 – 2024. Each dot represents a year.

As with the first chart, this one is a mess but there are some things you notice when you squint. Is this the case because, as we established earlier, frequency is up? More storms in a season = more total ACE in that season. Said differently, higher ACE in a season does not necessarily mean that severity is up. Here is annual ACE adjusted for the number of storms in the respective season.

Even squinting hard, it's difficult to see any sort of trend here. This leads one to believe that in addition to major storms becoming more frequent, so are less severe storms. Perhaps 'Storm XYZ' that would have been a Tropical Depression in 1990 now ramps up to a Tropical Storm or Category 1 Hurricane in 2010.

Major Hurricanes

How about an increase in both the absolute and relative number of major hurricanes? Part of the idea is that once minor storms now have the ability to evolve into major storms (category 3, 4 or 5 storms). An increase in the sheer number of major storms would justify this idea. Similarly, an increase in the number of major storms relative to the number of total storms in a year would mean that major storms are disproportionately more common than minor storms.

There is a noticeable increase in the number of major storms, certainly after 1975 and then again after the mid-1990s. When looking at these storms relative to the number of total storms in a season, a trend is far less obvious. In recent years, there are far fewer seasons with major storms accounting for 0–10% of all storms, and many more years of major storms accounting for 10–30% of all storms.

Damage

All metrics we have looked at so far have (rightly so) been focused on physical attributes of actual hurricanes. Being humans, we naturally care about what impact these storms have on our lives and the most immediate, short-term impact is the destruction they leave behind. Looking at the damage these storms cause can be tricky for several reasons.

First, any figure on damage caused by a storm is inherently an estimate. While these estimates have likely improved over time, estimating damage in dollars is less certain than a barometer reading pressure or an anemometer measuring wind.

Second, damage greatly depends on the path a storm takes. All else being equal, would you expect more damage to be caused by a storm passing over Wealthy Estates, with its newly renovated schools and expanded downtown shopping center or Barren Boondocks, with its outdated town hall and rural neighborhoods? Similarly, if a storm takes a horizontal path through Miami and across the Gulf of Mexico to Houston, that storm will cause more damage than the exact same storm that never makes landfall.

Third, keep in mind the exponential increase in the cost of things over time, due to both technology and inflation. The average car in 2024 might have a larger screen than the average television in a house built in the 80's. Similarly, a house destroyed in 1985 would likely be cheaper to replace than a house built on the same lot in 2015. As technology continues to be placed in everything we use and inflation persists, this trend will only increase.

With these important considerations in mind, here is the estimated damage each storm inflicted in USD. Dollar figures are measured in the year which the storm occurred.

The question of increasing frequency and severity is an important one that is best measured in a variety of metrics. Using the data above, we can see a gradual and noticeable changing of the tide. There is evidence that more major storms are forming in the Atlantic over time, but perhaps most important is the idea that once minor storms are becoming stronger. The once tropical depression may now become a tropical storm. The once tropical storm now more easily forms into a category 1 hurricane. The category 1 graduates to a 2, the 2 to a 3 and so on.

Which lineup do you think worries a Major League pitcher more, the one with 2 future hall of fame hitters and 7 minor leaguers or the one with 7 all-star hitters and 2 minor leaguers? There is a case to be made for either. In the present day, what unfortunately seems to be a more realistic lineup is something like 2 future hall of famers and 7 all-stars. That combination of legendary talent combined with unabated skill could give even the best pitcher the yips.