Mean reversion is the concept that, over a longer time horizon, extreme events or infrequent streaks are offset by more frequent outcomes.
Sunshine follows rain. Shameful Wordle scores follow the boast. Tails fails despite what “they” say.
However, since the mean reversion relates to recent hurricane seasons, the immortal words of Caddyshack Judge Elihu Smails apply.
“Well, we’re waiting.”
And we will most likely wait even longer until everything is close to normal.
Every hurricane season since 2016 has had above-average activity, all ending in the top third of the years since 1950.
A ludicrous 101 named systems in 2017-2021 have accumulated the most accumulated cyclonic energy (ACE) of any five-year period in hurricane climatology, brutally translating into 32 named storms, 15 hurricanes, and 7 major hurricane landfalls on the continental US coast.
In short, relentless tropical turmoil has been one of the top three worst things to happen in the past six years, along with the slow destruction of Everything You Love and a lack of new music from “Weird Al” Yankovic.
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WeatherTiger’s odds are not in our favor
WeatherTiger’s initial forecast for the 2022 Atlantic hurricane season offers limited hope for more typical threats in the coming year.
Our seasonal forecasting algorithm predicts a most likely outcome of approximately 155% of average activity. Normal ACE has been around 100 for the past fifty years, so our forecast puts a most likely outcome of around 155 ACE units in 2022, or roughly midway between the final numbers of 2020 and 2021.
When broken down, that means we have a 70% chance of an above average season, a 25% chance of normality, and just a 5% chance of an below average season.
There is a 35 percent chance of 2020-like “hyperactivity” (>165 ACE) and a 35 percent chance of a more active year with more garden diversity (125-165 ACE) like 2021. The season is expected to be 22 begins the ranges of 105-200 ACE units, 16-23 tropical storms, 7-11 hurricanes, and 3-5 major hurricanes.
Trust sells, which is why there are no platinum rap albums titled “My Haters Make Some Valid Points.”
At the risk of undermining my alter ego, DJ Endle$$$hrimp, the outlook for spring hurricane season is inherently uncertain.
WeatherTiger’s April forecasts have demonstrated a small but significant capability of 15-20% over the climatology, as good as or better than other forecasts released this time of year.
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A strangely persistent La Niña is a bad sign
The primary source of this limited predictive power is the tendency of unusually warm (El Niño) or cool (La Niña) waters in the equatorial Pacific, collectively known as the El Niño-Southern Oscillation (ENSO), to persist through the peak of the hurricane season. Atlantic hurricane activity is closely related to ENSO as fall El Niños are associated with hurricane-weakening wind shear in the Atlantic.
Thus, La Niña hurricane seasons average about 75% more ACE than El Niño years. The disparity is even greater in terms of impact, since La Niñas has averaged more than twice as much US landfall activity as El Niños since 1900.
Unfortunately, long-term projections of spring ENSO conditions hit a “predictability barrier” of reduced predictive ability. Sudden shifts in the Pacific are most common at this time of year and have outsized, long-lasting impacts on global weather patterns.
A historically unusual moderate La Niña is key for the forecast this year.
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La Niña events tend to last a winter or two, with only three triple dips in the past 75 years, most recently when a 1998 Niña also took over in 1999 and 2000.
Earlier this year the cold pool was easing and it seemed like the typical sinking of a second winter Niña was on the way; however, cool anomalies in the Pacific have since stabilized at about 1⁰C below normal, and La Niña looks like a good bet for a third straight summer, according to WeatherTiger’s ENSO models.
With no significant reserves of warmer water lurking beneath the surface of the Pacific, La Niña is more confident than usual, or at least cool, neutral conditions will continue into the fall, ushering in a busy Atlantic hurricane season.
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Signs of another early hurricane season on the horizon
Another aspect of the spring outlook, besides ENSO, is anomalies in Atlantic water temperature. Historically, the strongest relationships between Atlantic springtime warmth and an active hurricane season are between eastern Brazil and the Gold Coast. Warm spring water there, often at the peak of hurricane season, migrates north into the main development region from West Africa to Central America, promoting more frequent tropical wave development.
This spring, the water temperatures in the equatorial East Atlantic are close to normal. However, the lower atmospheric temperatures in this region were mostly above average in March.
This signals the probable beginning of a trend toward warmer-than-average Atlantic SSTs into summer, a pattern that has repeated several times over the six years. Fool me once, shame on me; fool me twice, don’t be fooled again.
Like last year, water temperatures are significantly warmer than average in much of the subtropical Atlantic, particularly north of the Bahamas and off the southeast coast. While the correlation of March sea temperatures in the area with annual hurricane activity is weak, this western Atlantic warmth could bode well for another early start to the hurricane season.
Again, the reality has exceeded the old norms, with seven straight years with a named storm ahead of the season’s official start on June 1st. The National Hurricane Center will issue tropical forecasts every six hours starting May 15, and an official change in hurricane season boundaries may follow in a few years. More on that in a future column.
During the last half decade and the transition, the US coast has endured a pitiful regime where the Gulf landfalls are heavy, the first storms come early and the hurricane seasons are all above average. Time will tell when Mean Reversion will give us some well-deserved respite, and there’s still a 30% chance that could happen this year. However, with an unshakable La Niña, the warmth of the Atlantic and the overall mood of 2022, I’m not trying to be optimistic.
Updates will also be released as needed if there is a US threat ahead of the season’s official launch, otherwise we will come out with a new seasonal outlook around June 1st. Until then, keep watching the sky.
dr Ryan Truchelut is Chief Meteorologist at WeatherTiger, a Tallahassee-based start-up providing advanced weather and climate analysis, forensic meteorology and expert consulting, and agricultural and hurricane forecast subscription services. For more information on WeatherTiger, visit weathertiger.com or contact us at [email protected]
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