The unforgiving 2020 Atlantic hurricane season, which has tormented coastal communities from Texas to New England, plowed into uncharted territory Monday evening when the 29th named storm was born. No previous season since reliable records began nearly 170 years ago has seen this many named storms — and it is not over yet.

The 29 storms are not only the mark of an unprecedented season statistically, but one that has left behind a devastating toll on the economy and people’s lives.

An unmatched 12 named storms, including a record-tying six hurricanes, have made landfall in the United States in 2020, leaving few areas on the Gulf and East coasts untouched. Parts of the Gulf Coast have been hit repeatedly, the state of Louisiana seeing a record five storms make landfall alone.

Several meteorological influences stacked the deck in favor of this punishing onslaught, while climate change may well have intensified the season’s activity and potentially expanded the zones in which storms have formed and gained strength. It may have also contributed to the season’s longevity.

The relentless season, which began unusually early and has not slowed, has racked up countless meteorological records while exhausting the conventional list of storm names and forcing forecasters to draw from the Greek alphabet for only the second time.

Mounting economic toll

The 2020 hurricane season has caused billions in damage in several states, with the epicenter in Louisiana. In late August, western Louisiana was slammed by Category 4 Hurricane Laura, tied for the strongest storm to ever hit the state. Six weeks later, Hurricane Delta struck only 13 miles east of where Laura had come ashore, exacerbating damage in communities such as Cameron and Lake Charles.

When Delta struck, for example, many homeowners in Lake Charles still hadn’t gotten their power and water access restored following Laura’s direct hit. The back-to-back storms forced thousands to be in an extended limbo, living in hotel rooms away from their battered homes and jobs.

Then, in late October, Hurricane Zeta hit Louisiana, its eye tracking directly over New Orleans before it brought damaging winds all the way to northern Georgia and Virginia.

According to Steve Bowen, head of catastrophe insight at Aon, Atlantic storms so far this season have caused an estimated $36 billion in damage. This is considerable, but far below record economic-loss years such as 2017 ($306 billion) and 2005 ($238 billion), when adjusted to today’s dollars.

“The best way to describe the 2020 season is: record-setting activity, costly, and it could have been much worse,” Bowen said in a Twitter message. “While no one is diminishing the significant humanitarian, physical damage, and fiscal impacts from tropical cyclones this year, we also have to breathe a sigh of relief. Several of the 12 U.S. landfalls this season occurred in some of the least densely populated areas along the U.S. coastline.”

Bowen said Hurricane Laura would have been far more damaging had it shifted east or west by 50 miles, which could have encompassed either New Orleans, where the city’s bolstered flood defenses are rated only for a Category 3 storm, or Beaumont, Tex., home to numerous oil and gas facilities.

“Regardless, this season has highlighted where we need to continue making improvements to coastal infrastructure, modernizing building codes, working to better retrofit vulnerable structures, and also more clearly communicate the wind and water risk to coastal and inland communities from tropical cyclones,” he said.

Why this season has been so busy

The historic season is a product of several overlapping oceanic and atmospheric cycles, which amplified storm formation.

The stage was set for the hyperactive season when a La Niña pattern became established in the tropical Pacific Ocean. Characterized by cooler-than-average waters in the equatorial tropical Pacific, its influences have an effect on the Atlantic by diverting the jet stream north and reducing hostile high-altitude winds. That makes it easier for tropical systems to form without being torn apart.

Simultaneously, a number of other factors favored an increase in rising air over the Atlantic. These features tend to circle the global tropics every 30 to 60 days, giving a boost to marginal storms that may otherwise struggle to organize. The timing of such features in the atmosphere helped maintain favorable conditions later in the season than usual.

La Niña has a similar effect, enhancing the large overturning circulation in the atmosphere north of the equator, known as the Walker Circulation. This spurs sinking motion and suppressed storminess in the Pacific while supporting continued rising and enhanced activity in the Atlantic.

All of those factors came together to provide a boost to fledgling storms.

The distribution of storms and their proximity to land has proved dangerous. The central and eastern tropical Atlantic, ordinarily host to a litany of systems, was atypically quiet. Instead, many systems this year formed in the Caribbean or the Gulf of Mexico, within close striking distance to the Lower 48 states.

A boost from climate change

Unusually warm water temperatures, due in part to human-induced, climate-driven warming, have also played a role in the season’s hyperactivity. Warmer waters are instrumental in allowing a storm to organize and strengthen, in some cases rapidly.

Nine of the season’s storms underwent periods of what’s known as rapid intensification, involving at least a 35 mph increase in the storm’s maximum sustained winds in 24 hours, said meteorologist Sam Lillo, a researcher at the University of Colorado at Boulder.

Some of these, such as Hurricanes Laura and Delta, underwent this intensification as they approached land, which has long been a nightmare scenario for emergency managers and until the past few seasons was rare in the northern Gulf of Mexico, where cooler continental shelf waters tend to weaken hurricanes as they approach the coast.

Hurricane Eta holds the record for the largest 24-hour intensification during 2020, having increased its winds by 75 mph in 24 hours as it neared Nicaragua, Lillo said in a Twitter message. Eta and Delta also increased their intensity by a staggering 105 mph in 36 hours.

“Prior to 2020, only FOUR storms had done this: Labor Day 1935, Andrew 1992, Wilma 2005, and Felix 2007. And now we have two in 2020,” Lillo said.

Scientists say rapid intensification, which has long occurred with the most intense hurricanes, is happening more frequently and in parts of the Atlantic basin where it didn’t used to, thanks in part to climate change.

While most studies show that climate change is not yet driving an increase in the total number of tropical cyclones, making a repeat of the 2020 season unlikely in the near future, it’s widely agreed in the scientific community that the storms that do form are already becoming more destructive.

First, rising sea levels worsen the damage from storm surge flooding. In addition, increasing air and ocean temperatures are allowing hurricanes to dump more rainfall once they hit land, causing deadly inland flooding, as illustrated by Hurricane Harvey in 2017.

“[W]e can say with confidence that hurricane impacts are worsening in a warming climate, from more intense and wetter storms on top of the backdrop of sea level rise, regardless of how frequency may or may not be changing,” said Allison Wing, a hurricane researcher at Florida State University.

Climate change may have also played a role in expanding the length of the season and the zone in which storms have formed.

With ocean surface temperatures five to seven degrees above average in parts of the Atlantic in June and early July, tropical storms “Dolly and Edouard were named on the outer edge of the envelope for all storms forming before August,” Lillo tweeted, while also noting Dolly formed farther north than any previous June storm on record.

Those outliers developed after tropical storms Arthur and Bertha formed in May, before hurricane season had even officially begun. Jim Kossin, an atmospheric scientist with the National Oceanic and Atmospheric Administration, said the preseason storm activity “seems to be, certainly, very attached to sea surface temperature.”

Then, in late October, Hurricane Epsilon rapidly intensified farther north and east than any previous storm so late in the season, Lillo found.

At the moment, two tropical storms, Eta and Theta, simultaneously roam the Atlantic for the first time this late in the season since 1887, according to Phil Klotzbach, a hurricane researcher at Colorado State University. A third storm, which would earn the name Iota, may form in the coming days over the Caribbean.

Outlooks missed the mark

While the 2020 hurricane season has been exceptionally active by most metrics, the total amount of energy generated has not reached historic territory because many of the storms that formed have been rather weak. By the metric known as Accumulated Cyclone Energy, or ACE, 2020 ranks as 11th most active. The 1933 and 2005 Atlantic hurricane seasons, the latter of which featured Category 5 storms Emily, Katrina, Rita and Wilma, still hold the top two spots for ACE.

Preseason forecasts called for a very active hurricane season, but none to the degree that has actually occurred. Outlooks issued in April and May mostly called for between 15 and 20 named storms.

The most aggressive and prescient preseason prediction was made by scientists at the Penn State Earth System Science Center, which called for a range of 15 to 24 storms, with a best estimate of 20. Yet even that has proved too conservative.