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The sixth straight busier-than-normal Atlantic hurricane season is over

It was the fourth-costliest hurricane season on record, with 21 named storms, including 7 that made landfall in the Lower 48 states

Floodwaters slowly recede in the aftermath of Hurricane Ida in Lafitte, La., on Sept 1. (Gerald Herbert/AP)

Producing an above-average number of storms for a sixth consecutive year, the 2021 Atlantic hurricane season officially comes to a close Tuesday. The season produced 21 named storms, the third most on record, only trailing last year and 1995. And for just the third time, the season exhausted all names on the National Hurricane Center’s conventional naming list.

While the season cranked out four major hurricanes, it will be most-remembered for Hurricane Ida, which slammed southeast Louisiana at near Category 5 status at the end of August. After razing areas in southeast Louisiana and unleashing gusts topping 150 mph, Ida’s remnants charged up the Appalachians and into the Northeast, bringing disastrous flooding and a tornado outbreak.

Largely due to Ida’s destruction, the 2021 Atlantic hurricane season is preliminarily the fourth most costly on record, with damage and losses expected to exceed $70 billion. It surpasses the toll inflicted by last year’s record 30 named storms, including an unsurpassed 11 that struck the United States.

Between the 2020 and 2021 Atlantic seasons, a record 18 named storms made landfall along U.S. shores.

Another above-average season

The 2021 season followed a spate of above-average or hyperactive hurricane seasons since 2016, a period marked by numerous direct blows to the United States. Harvey, Irma and Maria formed in 2017, Category 5 Michael slammed the Florida Big Bend in 2018, and Dorian sideswiped the Carolinas in 2019 after ravaging the Bahamas. Last year’s unrelenting tempests included Category 4 Laura in southwest Louisiana, an area that would be hit by Delta barely six weeks later.

NOAA attributed the six-year active stretch to a multi-decadal oscillation that favors busy hurricane seasons; it wrote the oscillation is probably tied to both natural and human-caused climate factors in a news release.

Meteorologists and atmospheric scientists turn to ACE, or Accumulated Cyclone Energy, as a metric of how active a season is. ACE is a product of storm intensity and duration, and attempts to quantify how much energy a system extracts from the ocean and expends on its winds. An average season racks up about 123 ACE units; this season scored an ACE of 145, about 18 percent above average. While hurricane season officially runs from June 1 through Nov. 30, much of the ACE piled up in August and September; only one storm developed in the past two months.

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Seven hurricanes, four major

While the 2021 hurricane season burned through the National Hurricane Center’s naming list rapidly, it was partly a product of how many quick-forming and short-lived systems there were. According to Phil Klotzbach, a hurricane researcher at Colorado State University, the season featured at least nine “shorties,” a storm that remains named for less than two days. That ties for the most on record in a single season.

The bulk of the ACE — upward of 73 percent — from this season came from the four major hurricanes, rated Category 3 or higher, that formed. Grace rapidly intensified in the Bay of Campeche in mid-August, lurching from a tropical storm to a Category 3 in 15 hours before making landfall in Veracruz, Mexico.

Then came Ida which, despite its intensity, didn’t remain at peak strength for long. That’s why its ACE was rather tepid — only 10.8 units — when compared to long-lived Larry’s and Sam’s 32.8 and 53.8 units respectively. The pair of major hurricanes roamed through the open North Atlantic, causing little impact other than in Newfoundland. That’s where Larry made landfall on Sept. 11 as a Category 1 hurricane, causing $80 million in damage.

Scientists drove a robotic surfboard into Hurricane Sam, and the waves were incredible

In addition to the four major hurricanes, three weaker hurricanes formed: Elsa, Henri and Nicholas. The seven total hurricanes was just slightly above the recent 30-year average of 6.4.

Remembering Ida

Arguably the climax of the 2021 Atlantic hurricane season, Hurricane Ida proved the most destructive with its multiphase and multifaceted array of hazards. The storm, which was well-forecast, first cropped up as a tropical wave Aug. 23, eventually being declared a tropical depression Aug. 26 in the Caribbean. A lack of wind shear, or a change of wind speed and/or direction with height, meant that Ida could develop without being subjected to an atmospheric tug of war. That allowed it to strengthen unimpeded.

It faltered briefly in strength Aug. 27 after colliding with Cuba as an 80-mph Category 1. Then it entered the Gulf where, in addition to calm upper-level winds, a “loop current” of exceptionally warm water fostered it into a major hurricane. It was declared a Category 3 on the morning of Aug. 29, and reached Category 4 status just an hour later as it explosively intensified. Ida then hovered just shy of Category 5 strength as it made landfall near Port Fourchon, La., with 150-mph sustained winds. A gust of 172 mph was measured by a ship in Port Fourchon, with nearby Leeville clocking gusts to 153 mph.

Ida’s impact from the Gulf Coast to Northeast — by the numbers

Virtually the entirety of New Orleans was left without power in the wake of the storm, where winds gusted to 90 mph. Ida spawned a number of weak tornadoes in the Deep South before shifting up the Appalachians. A rare “high risk” of flash flooding was hoisted in New York City and near/west of the Interstate 95 corridor in the Northeast, where high-end flooding was expected.

On Sept. 1, Ida’s remnants precipitated a significant tornado outbreak in the Mid-Atlantic and in New Jersey, with a number of Midwestern-style twisters carving through places like Annapolis, Md., and Mullica Hill, N.J. Later that night, Ida’s tropical moisture merged with a cold front to dump extreme rainfall totals with astonishing rainfall rates. A whopping 3.15 inches was recorded in an hour’s time in New York’s Central Park with 3.24 inches in an hour at Newark International Airport; both set one-hour records. Newark wound up with 8.41 inches on Sept. 1 alone, the city’s heaviest calendar-day total dating back to at least 1931.

Here’s what made the New York City flooding from Ida so devastating

In the end more than 50 people died in the Northeast from the flooding, and nearly three dozen tornadoes were confirmed. The Mullica Hill, N.J., tornado was rated a high-end EF3 on the 0 to 5 scale for intensity.

Other storms in 2021

There were several storms beyond Ida that left a mark stateside, but the United States largely evaded what could have been an even more severe slew of storms. Tropical Storm Elsa swept up the East Coast in early July with heavy rainfall. Henri also swept through New England on Aug. 22, making landfall near Westerly, R.I., with 60-mph winds, but its wind effects were dwarfed by more than eight inches of rainfall in New Jersey associated with rains fueled by the storm’s moisture.

Nicholas made a brief foray into hurricane status on the night of Sept. 13 as it made landfall near Sargeant Beach, Tex., with 75-mph winds. That wound up being the last storm to directly affect the United States in 2021.

Contributing to the above-average season was a fledgling La Niña, which favors increased rising air in the Atlantic, as well as anomalously warm water temperatures across most of the basin, including the Gulf of Mexico and Caribbean. It’s likely that human-induced climate change is a driver of the warming sea surface temperatures, as well as a major factor in the increased frequency and rate of rapid intensification observed in recent years.

How climate change helped make Hurricane Ida one of Louisiana’s worst

The Atlantic largely shut off in October and November thanks to an uptick in wind shear, which is pernicious to nascent storms, spelling an early end to the season.

The official end date of hurricane season, however, doesn’t mean Mother Nature always plays by the calendar. Once in a great while, named storms have formed in the Atlantic in December and even January, although it is rare.

Forecasters correctly predicted the 2021 Atlantic season would be an active one, although the overall number of storms slightly exceeded their expectations.

The 2022 Atlantic hurricane season officially kicks off June 1. However, forecasters are considering moving up the start date to May 15 due to a recent increase in May storms (2021 was the seventh year in a row a named storm formed before June 1), probably linked to climate change.