Very active and very odd: A 2021 Atlantic hurricane season review

The 2021 Atlantic hurricane season was the second hectic season in a row following the record-breaking 2020 season, with new storms spinning up in rapid fashion and very few breaks between each new system. However, due in part to an almost entirely inactive homestretch, the Atlantic hurricane season actually wound up slightly below average in terms of the total number of hurricanes and above average in terms of the total number of named storms.

AccuWeather meteorologists predicted the 2021 season nearly to a T back in March, calling for 16 to 20 named systems, between seven and 10 hurricanes, and three to five major hurricanes. By the end of the season, which officially ends on Nov. 30, this prediction was nearly spot-on with 21 named storms, seven hurricanes and four major hurricanes.

For the seventh straight year, the first storm of the year spun up before the official start of the Atlantic hurricane season, which begins on June 1. This long-term trend has raised some questions about whether or not the official start of the hurricane season should be moved to earlier in the year, a debate that is still ongoing.

Tropical Storm Ana formed on May 22, a precursor of a spell of early-season storms that was about to come.

Bill, Claudette, Danny and Elsa all hit in quick fashion in late June into July, with Claudette and Elsa pelting the storm-weary Gulf Coast, which took the brunt of the 2020 hurricane season. AccuWeather National News Reporter Bill Wadell met with Louisiana residents in July who were still frustrated as they continued to deal with the aftermath of the previous hurricane season as the 2021 season was ramping up.

Lake Charles, Louisiana, resident Jennifer Smith spoke with Wadell 11 months after Hurricane Laura bombarded the region, explaining that repairs still needed to be finished following last year's hurricanes. "We've been through a whole lot and still need help," Smith said. Others echoed Smith's sentiments as the 2021 season was heating up.

Hurricane Elsa capped off the flurry of early-season activity before a break in the pattern gave residents and forecasters a chance to catch their breath and prepare for the next chapter of the hurricane season, which was right around the corner.

Tropical Storm Fred developed on Aug. 11 and kicked off a blitz of storms that lasted nearly two months. Between Aug. 11 and Oct. 5, there were only two days on which there was not a named storm in the Atlantic basin. During this period, there were 15 named systems, keeping pace with the 2020 hurricane season and nearly exhausting the list of predetermined names for tropical systems in the 2021 season.

Lake Charles resident Jennifer Smith. (AccuWeather / Bill Wadell)

After the near record-setting procession of storms, tropical development came to a screeching halt in mid-October as a shift in the weather pattern across the Atlantic hindered the formation of any new systems. AccuWeather meteorologists saw the pattern developing in October that would create an environment that was inhospitable for tropical development and, with six weeks to go in hurricane season, forecast that the once fast and furious hurricane season was all but over.

This abrupt end in the tropical activity contributed to a unique record. According to Dr. Phil Klotzbach, a meteorologist from Colorado State University, 2021 was the first year since the start of the satellite era in 1966 in which there were no major hurricanes anywhere in the world between Sept. 25 and Nov. 19. Since Klotzbach made that observation, the streak in which there are no major hurricanes has continued and, as of Nov. 30, stood at 66 days.

Dan Kottlowski, AccuWeather's chief hurricane forecaster, explained that this was in part due to fewer tropical features coming off the coast of Africa. These topical waves are the most likely candidates to spin up into a named tropical system. Additionally, an uptick in wind shear also prevented any tropical development in the latter stages of hurricane season.

It wasn't until Halloween that the 21st and final storm of the season took shape. Subtropical Storm Wanda formed over the northern Atlantic from the remains of a nor'easter that hit the East Coast earlier in October. The system eventually transitioned to a tropical storm, but it failed to strengthen into a hurricane.

Wanda was a low-impact tropical system, spending most of its life spinning harmlessly over the open Atlantic, but it had significance. It claimed the final name of the pre-determined list of designated storm names for the season.

With Wanda capping the season, 2021 became only the third year in history that the list of names had been exhausted, joining 2005 and 2020.

Earlier this year, new Atlantic basin 30-year "climate normals," which take into account 30 years of tropical storm and hurricane data spanning the period from 1990 to 2020, were implemented. Between 1990 and 2020, the Atlantic basin averaged 7.2 hurricanes per season, meaning that the seven hurricanes tallied during the 2021 season made for an ever-so-slightly below-average year.

With a total of 21 named storms, the 2021 season turned out to be about 50% above average, and, in terms of the number of major hurricanes, storms that reach Category 3 force or higher, 2021 proved slightly above average. Four storms -- Grace, Ida, Larry and Sam -- all reached major hurricane status and exceeded the 30-year average of 3.2 major hurricanes per year.

In previous years, additional systems were named after letters of the Greek alphabet, but following the hyperactive 2020 season, the World Meteorological Organization decided to create a supplemental list of names to be used. This new list is similar to the initial list, starting with a name that starts with the letter A and works its way through the alphabet, with the exception of names beginning with the letters Q, U, X, Y and Z.

Meteorologists did not have to tap into this backup list since Wanda was the final storm of the season. However, given the past two seasons, it may be only a matter of time before the extra list of names needs to be used.

The Gulf Coast, which was bombarded during the 2020 season, experienced six landfalls in 2021, including four tropical storms and two hurricanes.

Tropical Storm Claudette was one of the more unusual storms to hit the Gulf Coast as it did not develop the same way that most storms do. Typically, tropical storms develop over water, but Claudette did not take shape until after it moved over Louisiana.

This is known as the "brown ocean effect," according to AccuWeather Senior Meteorologist Alex Sosnowski. "The area over Louisiana where it was dubbed a [tropical storm] is fairly swampy, so there is still some warm water involved," Sosnowski explained.

Tropical Storm Mindy was another strange storm that drenched the Gulf Coast, taking shape just hours before moving over the Florida Panhandle. The storm quickly traversed northern Florida and southern Georgia to emerge over the open waters of the Atlantic Ocean where it fell apart just 30 hours after it formed.

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One of the most memorable aspects of the 2021 season will not be the storms that hit the Gulf Coast, but those that walloped the Northeast.

The first was Hurricane Henri, which was something meteorologists refer to as a "home brew" system because it started as a complex of thunderstorms over the middle of the U.S. The thunderstorms then traversed the eastern U.S., organized over the warm waters of the Atlantic Ocean and eventually evolved into a Category 1 hurricane.

Henri then took an unusual path as it circled back around to the U.S. and threatened to make landfall as a hurricane. After a close call with Long Island, New York, Henri made landfall in Rhode Island as a strong tropical storm on Aug. 22. Henri was the first tropical system to make landfall in Rhode Island since 1991 and soaked residents and vacationers alike all across the Northeast.

The zig-zag track of Henri from the time that it took on tropical characteristics through its encounter with the Northeast. (AccuWeather)

The unbalanced nature of the storm unloaded significant rainfall over New Jersey and New York during one of the final weekends of summer when families flock to beaches. Rainfall totals between 6 and 12 inches were common, including nearly 10 inches in Brooklyn.

Henri was a preview of what was about to come, as the next storm that developed was one of the strongest and most impactful storms of the entire hurricane season.

Just two days after Henri dissipated, Ida took shape, beginning as a tropical storm over the Caribbean Sea. In the following days, it tracked over the warm water in the Gulf of Mexico and strengthened into a major hurricane as it charted a course toward Louisiana.

Ryan Madigan, and his daughter Charolette Madigan, 11, of Cold Spring Harbor, N.Y., stand along a beach in Montauk, N.Y., Saturday, Aug. 21, 2021, as Hurricane Henri churns up waves as the storm approaches. (AP Photo/Craig Ruttle)

Ida was significantly stronger than Claudette, roaring ashore at peak strength on Aug. 29 as a Category 4 hurricane with maximum sustained winds of 150 mph, just 7 mph shy of Category 5 status. It also tied Hurricane Laura as the strongest storm on record to make landfall in Louisiana in terms of wind speed.

However, the most destructive side of Ida didn't rear its head until Sept. 1 when it transitioned to a tropical rainstorm and unloaded a deluge across the mid-Atlantic. Multiple flash flood emergencies were issued across Pennsylvania as Ida dropped a month's worth of rain in just a few hours. Deadly tornadoes also spun up in eastern Pennsylvania and New Jersey with a rare tornado emergency being issued for Trenton, New Jersey, the state capital.

By nightfall, the worst of the rain focused on New York City where walls of water gushed into the ground floors and basements of buildings all across the city.

"The torrential rain from Tropical Rainstorm Ida resulted in the most significant flash-flooding disaster in New York City history," AccuWeather Chief Meteorologist Jonathan Porter said at the time.

More than 80 fatalities from Louisiana through New York were blamed on Ida, including at least 52 deaths across the Northeast, ABC News reported. This made Ida the deadliest storm of the entire season, as well as one of the costliest with nearly $100 billion in damage and economic loss, according to AccuWeather founder and CEO Dr. Joel N. Myers.

As devastating as the landfalling systems were throughout the year, some of the strongest storms of the season did not come close to the contiguous U.S., but they still had a major impact on the season as a whole.

One way that meteorologists analyze tropical cyclones is with a value known as accumulated cyclone energy (ACE). This index summarizes how much energy a storm has produced throughout its lifetime.

"Storms that exhibit large ACE values are going to be the storms that not only have very strong winds but have them over a long duration of time," AccuWeather Meteorologist Randy Adkins explained.

After Tropical Storm Wanda, the cumulative ACE for the entire 2021 Atlantic hurricane season was 145.1, according to Colorado State University. This is above the average of 122, but below the ACE for last season, which was 179.8.

While the ACE for the entire season was above normal, just two hurricanes accounted for 60% of the ACE for the season.

Hurricane Larry and Hurricane Sam were two long-lived and strong hurricanes that churned over the Atlantic for weeks but never made landfall in the U.S. The long-lasting nature of the hurricanes meant that they both generated a plethora of ACE that bolstered the statistic for the season as a whole.

This satellite image shows Hurricane Sam shortly after strengthening into a Category 4 storm on Sept. 25, 2021. (NOAA/GOES-EAST)

Sam was the stronger of the two, lasting as a major hurricane for more than a week and peaking just shy of Category 5 strength. This storm alone generated an ACE of 53.8, accounting for 37% of the ACE for the entire hurricane season.

For comparison, Ida, which was a hurricane for only around three days, had an ACE of only 10.8.

While the official Atlantic hurricane season draws to a close, the door is still open for another system to spin up, although it is unlikely.

There have been only 17 tropical systems to spin up in December across the Atlantic basin since records began in 1851. An unnamed subtropical storm was the most recent December system that formed, back on Dec. 5, 2013. Of all of the December storms, none have made landfall in the contiguous U.S.

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