How Busy Was the 2020 Hurricane Season?

How Busy Was the 2020 Hurricane Season?

by Neil L. Frank

The 2020 Atlantic hurricane season, with 30 named storms, is going down in the record books as having the most named storms of any season on record. But are we comparing apples and apples—or apples and oranges?

Some people blame the recent increase in named storms—tropical storms and hurricanes—on global warming, and infer that we must stop spewing CO2 into the atmosphere to curb the warming and so prevent the increase in storms and the damage they cause.

But the raw data for hurricane history is contaminated by changes in observing tools, in our understanding, and in the philosophy of whether a storm should be named. What explains the increase in named storms? Was it an abnormal meteorological event, or are there other explanations? To answer this requires some discussion of the origin of Atlantic storms.

How Do Atlantic Storms Begin?

One of the requirements for a tropical storm is a pre-existing weather disturbance that is producing thunderstorms. In the Atlantic during the summer, there are four categories of pre-existing weather disturbances. Two have their origin in the deep tropics, and two mainly in subtropical latitudes.

The most common tropical disturbances are African systems. Every 3 to 5 days, a new disturbance emerges from Africa. Trade winds carry these westward across the Atlantic Ocean, the Caribbean, and sometimes all the way to the Pacific. Every summer we track around 50, and about 10% develop into named storms.

A second category of tropical disturbances is found along the Intertropical Convergence zone (ITC)—a boundary where winds from the northern hemisphere clash with winds from the southern hemisphere.

The developmental process for weather disturbances found in the deep tropics is very straightforward. They generate thunderstorms that heat the atmosphere, and as the hot air rises it is replaced by air spiraling at the surface, producing a tropical storm. We can call this “tropical energy.”

The development process for pre-existing weather disturbances that originate in the subtropical latitudes (Central and North Atlantic) is far more complex. In this case the initial energy driving the disturbance is baroclinic—a term denoting winds that are generated when cold air moves under warm air. All winter storms are driven by this type of energy.

Over the Atlantic during the summer, two types of baroclinic systems operate to produce tropical storms. One occurs mainly during the spring and fall, when a low-pressure system develops along a dissipating cold front that has moved offshore from the U.S. mainland and stalls.

A second type occurs in the upper part of the atmosphere (25,000 ft. and higher). Occasionally, one of these “upper lows” strengthens and spins downward to the surface and may generate a named storm.

Some baroclinic disturbances can convert into tropical storms, and the process by which they do so is complicated. Consider the following scenario. In late May a cold front moves off the mid-Atlantic coast and stalls. A disturbance develops along the front and strengthens. Winds reach 45 mph. The initial energy is all baroclinic. However, thunderstorms generated by the disturbance warm the atmosphere, and now the system is being driven by both baroclinic and tropical energy.

Should the system be named a “tropical storm”? Not unless the tropical energy completely dominates the baroclinic energy. Occasionally this does occur, and the system morphs into a tropical storm.

Once they decide to name the storm, forecasters face another problem. As the storm moves toward the north Atlantic, thunderstorms decrease because of colder water, and cold air is drawn

into the circulation. The winds have not decreased, but baroclinic energy again dominates, and the system is unnamed as it transforms into a post-tropical remnant storm.

To Name or Not to Name? That Is the Question

The decision to name or unname this type of systems is very subjective, since we do not have an objective way to measure the contribution of each energy source. That is why forecasters in the past have been reluctant to name baroclinic-initiated storms.

Forecasters were faced with this decision four times in 2020, and each time they chose to name the system: Dolly, Edward, Kyle, and Omar. All four started out as baroclinic disturbances along dissipating cold fronts and then morphed into tropical storms under the influence of heat from thunderstorms. But following a very short tropical life of less than 24 to 36 hours, re-examination revealed that baroclinic energy once again dominated, and they were reclassified as post-tropical remnant lows (winter-type storms). This year we even named a baroclinic storm approaching Europe—Alpha was named a few hours before making landfall in Portugal.

Would these storms have received a name 30 or 40 years ago? Probably not, and data show this to be true.

The historical record of baroclinic-initiated tropical storms in the subtropical Atlantic north of latitude 25N for the past 75 years also reveals a recent trend to name more storms of this type. If we divide the 75 years into three 25-year periods, the first (1946–1970) is pre-satellite. Satellite pictures did not become available to operational forecasters until the late 1960s. This left us unable to observe storms in vast stretches of the Atlantic. During this time, under one storm per year (0.7/yr.) could be traced back to a baroclinic origin.

Satellite pictures were available during the second 25-year period (1971–1995), allowing us, for the first time, to detect storms in those vast stretches, which explains why there was a slight increase in the number of baroclinic systems, to 1.7 per year. 

A big surprise occurred in the years 1996–2020, when there was an unexpected jump to 4 per year. A big part of the increase took place during the last decade, when the number increased to 5 per year.

Another study confirms this trend.  During the 1970s and 1980s, over 50% of all named storms in the Atlantic were initiated by African systems. Another 10–15% were generated by disturbances on the ITC. It is not surprising to find that almost 70% of all named storms in the Atlantic trace their origin to weather disturbances whose origin was in the deep tropics. Fewer than 30% of Atlantic named storms originated as baroclinic systems (~15% by stalled cold fronts, and ~15% by upper–level lows).

Similar statistics for the last decade (2011–2020) show a significant increase in the number of baroclinic systems being named. Currently, 45% of named storms are caused by baroclinic systems, while the other 55% come from tropical disturbances.

The numbers for 2020 confirm the trend to name baroclinic disturbances. Thirteen of the 30 storms had a baroclinic origin, and 10 of those occurred in the subtropical Atlantic.

The number of named storms generated by tropical disturbances has not decreased, but there has been a significant increase in the number of named storms generated by baroclinic disturbances. Has there been a change in the philosophy of naming baroclinic-driven, winter-like storms that occur in the summer? If so, does this contaminate the historical record of Atlantic hurricanes, making more the numbers for the last 25 years not directly comparable with the numbers for the previous 50?

Without question satellites account for some of the increase in the number of detected and named tropical storms. One recent study examined the number of tropical storms that formed over the eastern Atlantic and never moved westward beyond longitude 50W. In pre-satellite years (1918–1968), we tracked an average of 1 storm every 2 years. During the satellite period (1969–2019), we tracked 2 to 3 per year—a 4- to 6-fold increase. This year 4 storms—Rene, Vicky, Wilfred, and Theta—fall into this category.

Another factor accounting for the increase in named storms was a subtle change in the requirements for naming a storm. Airplanes are used to determine the strength of a storm. They measure the winds at flight level and drop an instrument in the eye to determine the central pressure. Since there is a direct relationship between wind and pressure, if you know one you can determine the other.

When investigating a weather disturbance, it is not uncommon for the plane to encounter an area of strong winds associated with a band of thunderstorms. Should the system be named? What does the pressure show? If the pressure is not low enough to justify the winds, in the past the system was not named until the pressure responded. Not so today. The current philosophy is to use the observed winds to name a storm regardless of the pressure. The result is a few more named storms, and an increasing number of storms that have a lifetime of less than 24 to 36 hours. This year Bertha was named based on wind alone an hour and a half before making landfall in South Carolina. Could this emphasis on winds be the reason why there are more baroclinic-generated named storms in the North Atlantic?

Another unique feature of the 2020 hurricane season was that 3 hurricanes hit Louisiana. Some media reported that that had never happened before. But Florida was hit by four hurricanes in 2005. And the most active hurricane season as far as landfalls was 1886, when seven hurricanes hit the Gulf coast. Three were in northwest Florida and four in Texas, and two of those in Texas were major (Category 3 or higher). The last major hurricane to hit Texas in October struck in 1886 and destroyed what was left of Indianola, a once thriving seaport of the south shore of Matagorda Bay.   

Maybe 2020 Wasn’t So Strange After All

In conclusion, the hurricane season in 2020 was very active, but was it record breaking?

Prior to the 29 named storms recorded in 2005 and 30 in 2020, 1933 held the record for the most in any one year with 21. It is revealing to take a close look at the 1933 hurricane season.

The deep tropics were on fire. Of the 21 storms, 17 were initiated by numerous African systems along with a few ITC disturbances. Only one baroclinic disturbance developed in the Gulf, and another three in the southwest Caribbean. No storms were tracked that developed from baroclinic disturbances in the subtropical Atlantic, and none were recorded in the Eastern Atlantic. Were there were no storms in these two areas in 1933? We do not know, because tools necessary to track storms in the eastern and northern Atlantic didn’t exist yet.

What we do know is that in 2020, with satellites and recon planes, 10 baroclinic storms developed in the subtropical Atlantic, of which 2 were east of 50W longitude. These 2, combined with 3 other African systems that weakened, make 5 in the Eastern Atlantic. A fair comparison of the 1933 hurricane season with 2020 would be to reduce the number of storms in 2020 by around 10. If we do that, 1933 is still one of the most active hurricane summers in modern times.

With all of the uncertainties in the raw data, the only credible indicator of any trend in Atlantic hurricane activity is to look at the major hurricanes (Categories 3–5) making landfall in mainland USA. A tropical storm or even a weak hurricane might have hit a sparsely populated region in the 1800s or the early 1900s and gone undetected. In contrast, all major hurricanes with winds in excess of 110 mph crossing the U.S. coastline in the last 175 years have probably been recorded.

Contrary to the claim that global warming is causing more named storms, over the past several decades the number of major hurricanes hitting the U.S. coastline has fallen. There were none for twelve years (2005–2017). This was the longest period on record without a major hurricane. On average, one major hurricane crosses the U.S. border every two years.

In contrast to mainstream media claims, there has been no increase in Atlantic hurricane activity in recent decades. As a matter of fact, world-wide there has been a 5–10% decrease in hurricane-type storms in the last 50 years.

Neil L. Frank, Ph.D., is the longest-serving Director of the National Hurricane Center (1974–1987) and served as Chief Meteorologist of KHOU-TV Houston, TX (1987–2008). He continues tracking and studying tropical storms in his retirement. He is a Fellow of The Cornwall Alliance for the Stewardship of Creation.

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Richard Greene
December 11, 2020 6:29 am

Excellent report on hurricanes, by an obvious expert.
99 out of 100
Loses one point for no charts or tables.

Joel O'Bryan
Reply to  Richard Greene
December 11, 2020 10:14 am

Agree. This is the kind of Expert analysis the Climate Faker alarmists will need to bury because they cannot refute it. It destroys their cherished argument on TC and climate change.
Also seemingly now forgotten by the climate fakers are the unprecedented 12 years between 2005 and 2017 when no major hurricanes Cat 3 or higher) impacted a US mainland shoreline.

Chris Wright
Reply to  Richard Greene
December 12, 2020 3:45 am

I think he loses many more points by not mentioning the standard ACE measurement (Accumulated Cyclonic Energy). Instead he wastes virtually all of the article by going on about the number of named storms. Naming storms is completely subjective and has nothing to do with science.
The only way to measure storms is to – well – use measurements. I believe this season was quite active, based on the ACE, but was nowhere near any kind of record.

The UK started to name storms just a few years ago. So now the number of named storms is infinitely greater than what it was a few years ago. What better proof of the climate change crisis do you need?

Trying to Play Nice
December 11, 2020 6:37 am

I think the number of named storms is a wonderful, objective criterion for proving AGW? What could be less objective than a group of people assigning names to weather systems (or are they climate systems)? /sarc off

December 11, 2020 6:46 am

Maybe they need to come up with a checklist to name a storm. Minimum ocean water temperature, pressure level at the core, closed circulation with a minimum size, minimum wind speed that must occur in all sectors of the center, must be in existence for a minimum amount of hours, etc. Take the guesswork out of it. The biggest thing to me is the minimum ocean water temperature.

We have N’Easters off Hatteras in the late fall that are much more potent than tropical systems earlier in the year and they are baroclinic. When you have very warm, moist air over the Gulf Stream interacting with a cold front coming down from Canada it can get very interesting. On the satellite they look like a hurricane.

Jim Whelan
Reply to  rbabcock
December 11, 2020 9:06 am

When you change the criteria, you make the values incomparable. When you improve the measurement methods you also make the values incomparable. That’s one of the main points of the article. Devising some new measurement doesn’t fix the problem. Readers of WUWT and those who pay attention know that comparing the incomparable is one of the main methods used to promote “climate change”.

Reply to  Jim Whelan
December 11, 2020 5:33 pm

The only thing changed was a bunch of f**** bullshyte. Nothing that matters to anyone rooted in f****king reality was changed. Christ on a f***king crutch.

Tom in Florida
December 11, 2020 6:49 am

The reason storms are named is mainly to make them easier to identify. You many not remember tropical system #1 in 1993 but you certainly remember Andrew, where it was and what it did. You may not remember tropical system #11 in 2005 but you certainly remember Katrina, where it was and what it did. We in Florida may not remember tropical system #3 in 2004 but we certainly remember Charley, where it was and what it did.
Of course one may not remember anything about hurricanes if they have no interest or are never affected by them, so it is all relative.

Reply to  Tom in Florida
December 11, 2020 8:17 am

No one who personally saw what Andrew did will ever forget, and that it was in 1992.

Tom in Florida
Reply to  bwegher
December 11, 2020 3:03 pm

That certainly makes my point. Thanks for the correction.

Pat from Kerbob
Reply to  Tom in Florida
December 11, 2020 8:25 am

Yes, i’ve never had to worry about hurricanes here in AB.

Instead, -40C hurts

Reply to  Pat from Kerbob
December 11, 2020 11:43 am

-40C hurts as bad as -40 °F here in the USA!

December 11, 2020 7:07 am

Excellent overview Neil. Glad this stuff is finally coming out. I too have observed this very liberal tendency to name storms. I call it political padding. The Bertha example you described equally applies to Barry from 2019.

Thomas Gasloli
Reply to  John Shewchuk
December 11, 2020 8:09 am

Oh, John, you know they will tell you it is just a coincidence that the information is always biased toward increasing climate hysteria. And that we are conspiracy theorist for pointing it out.

Joel O'Bryan
Reply to  John Shewchuk
December 11, 2020 10:31 am

Barry from 2009-2017 was indeed a disaster.

Steve Case
December 11, 2020 7:29 am

In contrast to mainstream media claims, there has been no increase in Atlantic hurricane activity in recent decades. As a matter of fact, world-wide there has been a 5–10% decrease in hurricane-type storms in the last 50 years.

Neil L. Frank, Ph.D., is the longest-serving Director of the National Hurricane Center (1974–1987) and served as Chief Meteorologist of KHOU-TV Houston, TX (1987–2008). He continues tracking and studying tropical storms in his retirement. He is a Fellow of The Cornwall Alliance for the Stewardship of Creation.

In contrast it would be interesting to know what the current Director of the National Hurricane Center has to say about naming on storms, the relationship between CO2 and these storms and the frequency of these storms over the last 50 years.

Mumbles McGuirck
Reply to  Steve Case
December 11, 2020 1:16 pm

Ken Graham is probably wise enough not to opine publicly on these matters if he doesn’t need to. To say anything one way or the other is to get half the population on your case.

Reply to  Mumbles McGuirck
December 11, 2020 5:43 pm

No, 1/2 the population don’t give a f**k, the other 1/2 don’t give a f**k. The only 1/2 that gives a f***k is the leftarded 1/2, and their opinion is irrelevant because they are a bunch of stupid f***ks.

Peter W
December 11, 2020 7:42 am

I now live in Florida, and since this “global warming” business has been a hobby of mine for the past 14 years I followed the hurricane season closely. I just shook my head at the ridiculousness of some of the hurricanes they named; it was obvious from the start that they posed no threat to anything other than ocean marine interests and never would have been detected or named back in the 1960’s

I noted with interest that the article did not mention the 1900 Galveston hurricane which resulted in the death of some 6,000 people and property damage in excess of 17 million 1900 dollars.

December 11, 2020 7:56 am

It was a very busy season for non-hurricanes. Actual hurricanes? Not so much.

Joel O'Bryan
Reply to  2hotel9
December 11, 2020 10:19 am

Louisiana did get more than their share this year as Dr Frank points out. But not unusually so.
Just as the having a run of 4 heads in a row in 30 tosses of a coin done every year would not be unexpected. The climate scam depends heavily on average folks not understanding statistics in order for the climate fakers to run their fraud and artifice.

Reply to  Joel O'Bryan
December 11, 2020 5:38 pm

No, they just got what Louisiana gets. Period. Full stop. Putting a name on every single rain squall that appears throughout the entire globe does not change a f****king thing.

Hoyt Clagwell
December 11, 2020 8:22 am

So my conclusion is that CAGW is now CAUSING more storms to be named!! That’s definitely a human contribution and can’t be blamed on nature.

(Sarc, and away!)

Bill Rocks
December 11, 2020 8:28 am

Dr. Frank,

Informative and fascinating. Thank you.

Climate believer
December 11, 2020 9:56 am

A decrease in the number of Tropical Cyclones (TC) as well over the Bay of Bengal.

The hypothesis that warmer global temperatures will enhance TC activity would seem to be wrong. If anything, an opposite outcome is suggested, one in which global warming will lead to fewer total numbers of TCs and fewer intense TCs.

AGW is Not Science
Reply to  Climate believer
December 12, 2020 7:13 am

“If anything, an opposite outcome is suggested, one in which global warming will lead to fewer total numbers of TCs and fewer intense TCs.”

And for those who have not bought the propaganda and are (strangely enough) more scientifically literate, that is expected. A warmer climate means BETTER “weather,” not worse. That’s one of the biggest lies the Climate Fascists are selling – the ridiculous notion that warmer climate means worse weather. 180 degrees wrong!

In a warmer climate, the coldest, driest air masses see the biggest increase in temperature, because they are the easiest air masses to warm, and because the Earth constantly moves heat from the tropics toward the poles. The result is the temperature DIFFERENTIAL between the tropics and the poles shrinks, and this, if you consult a book on basic meteorology, as Richard Linzden so succinctly put it, will REDUCE “extra-tropical storminess,” NOT increase it.

Why do you think every previous WARM period during the current epoch, the Holocene, was called a “Climate OPTIMUM?!” Because the weather was so bad?!

The only thing getting worse about the weather is the HYPE about the weather.

Rud Istvan
December 11, 2020 10:06 am

Excellent post.
There is a similar observational change to tornados when Doppler weather radar got widely deployed in the US. Lots more F1’s after than before. Not much change in F3+ major tornados because those usually cause newsworthy damage. Good book about this is ‘Warnings’ by Mike Smith.

Jim Steele
December 11, 2020 10:08 am

Excellent informative post Neil. Thanks

December 11, 2020 12:38 pm

2020 U.S. Hurricanes

“All we want are the facts, ma’am” (fictional Sgt. Joe Friday, Dragnet, U.S. TV crime series, 1951-1959 & 1967-1970). Today’s news and news releases, even by government agencies, companies and universities, are anything BUT the facts. We now live in the era of Internet and social media “influencers.” Thus, Neil Frank admirably seeks to unravel the influencers and their agendas and get to the facts, as Sgt. Joe would say.

Since Neil well establishes that named storms is a farcical metric, I tried searching for a somewhat more “reliable” means to judge the season, landfalling U.S. hurricanes. Surely that is a “can’t miss” metric, or is it? First off, if you search for “U.S. land falling hurricanes 2020”, you are treated ad infinitum, ad nauseam to news stories and press releases about the record breaking Atlantic hurricane season. Even NOAA’s National Hurricane Center (NHC) breathlessly reports on the worst season eva! Buried deep within, with careful searching, you can find the storms that actually made U.S. landfall as “hurricanes,” but you have to dig even deeper to learn “factual” information about them.

You can’t simply go to the NHC website for a fact-filled summation. For example, their map of 2020 storm tracks has a color coded system that only distinguishes major hurricanes (magenta) from every other lesser hurricane (red). According to the map, one hurricane was “major” at landfall and five were just “hurricanes” (red) without differentiation. The map key doesn’t help, because it lists the maximum estimated sustained winds at any point along the track of each storm, not their estimated strength at landfall. If one looks up each hurricane individually on Wikipedia, while loaded with hyperbole, most of the six descriptions do manage to mention the estimated maximum sustained winds at landfall, but even this gets vague when a hurricane strength is near the boundary between Saffir-Simpson categories. The media’s tendency is to stretch the numbers to make the storm appear the worst possible.

From NHC archived reports:
Hanna – Cat 1 (peak estimated sustained wind at landfall ~90 mph)
Isaias – Cat 1 (peak estimated sustained wind at landfall ~85 mph)
Laura – Cat 4 (peak estimated sustained wind just before landfall ~150 mph, although NHC reported at 4AM just 3 hours after landfall on 8/27/20 that surface observations, Doppler radar and model guidance estimated winds at 105 knots [121 mph], Category 3)
Sally – Cat 2 (peak estimated sustained wind at landfall ~105 mph)
Delta – Cat 2 (peak estimated sustained wind at landfall ~100 mph)
Zeta – Cat 2 (peak estimated sustained wind at landfall ~109 mph)

Rarely if ever does the NHC bother to record and compare maximum surface observations at landfall with their aircraft-based, modeled estimates. Of course, the excuse is that it is not likely that the maximum sustained wind happens to occur at sensor height at the location of a surface station. True, but how was it measured before hurricane hunters, Doppler radar and models?

If these estimates are to be believed, the U.S experienced just one major hurricane in 2020, not at all unusual and not a record, and two hurricanes were only category 1 and the rest category 2. Which returns me to my last point about using measurement data for categorizing storms. In earlier times, hurricanes were categorized based on actual near surface measurements, not modeled estimates calculated from hurricane hunter aircraft and Doppler radar. Again, we have the “apples to oranges” comparison problem discussed by Neil Frank regarding naming of storms. During hurricane landfalls, I have repeatedly searched for sustained wind reports from weather stations and buoys, and rarely if ever do data even approach the NHC estimated values. This has been a common topic of commentary on WUWT. Without conducting thorough research on past storms to estimate winds based on photographic evidence of observed damages, we can only surmise that many historic U.S. landfalling tropical storms and hurricanes would have been reported as somewhat worse using today’s standards. Conversely, if we were to use empirical station data only, how many modern storms would have to be downgraded?

AGW is Not Science
Reply to  Pflashgordon
December 12, 2020 7:22 am

Exactly. It’s the “apples vs. hockey pucks” comparison, as usual. Always used to make it look like things are worse than they are in order to drive the climate hysteria. Same with “proxy derived” CO2 vs. instrument measured CO2, and “proxy derived” temperature vs. instrument measured temperature.

Naomi Oreskes likes to call those skeptical of AGW induced catastrophe the “Merchants of Doubt.” I call those pushing the AGW propaganda the “Merchants of Bullshit,” because that’s what they are. Snake Oil salesmen in a “scientist” costume.

Mumbles McGuirck
December 11, 2020 1:32 pm

I recall that when Neil was NHC Director, the hurricane specialists had a rule of thumb to wait 24 hours after a tropical depression formed before upgrading it to a named tropical storm. This reduced the chances of a short-lived high wind ob causing such a system being upgraded.

A decade or so later such caution was thrown to the wind. Specialists now will upgrade a disturbance directly to named status if a recco reports storm-force wind anywhere near it. There’s been a change in the culture at NHC that has resulted in an inflation in named storms. ACE is a much better metric for basin activity.

December 11, 2020 1:43 pm

Don’t forget that the hurricane season has been lengthened by 6 weeks since tracking began. The season duration (in the Caribbean, Gulf, Atlantic) was initially June 15 through October 31 (19 weeks), eventually becoming June 1 through November 30 (25 weeks), in 1965. This change is a 32% increase.

Mumbles McGuirck
Reply to  Nik
December 11, 2020 2:37 pm

However, storms can still be designated even if it’s not hurricane season. Hurricane season had more to do with bureaucratic considerations than tropical activity. During hurricane season the specialists have to do shift work etc. But the tropics are still monitored 365 days a year.

Bill Powers
Reply to  Nik
December 12, 2020 8:53 am

Was a time we didn’t name tropical storms, only hurricanes. Now they name every little name drop in order to up their hobgoblin count. And yes I know that last bit was cynically hyperbolic

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