After each hurricane season, the National Hurricane Center pens detailed write-ups that require them to meticulously review each storm that formed. Once in a while, they encounter new data that changes how they categorize storms.

A report released Tuesday on Hurricane Zeta, which struck Louisiana in October, suggests the storm was at Category 3 strength at landfall in late October. Five fatalities have been attributed to the storm, which made landfall in Cocodrie, on the Louisiana Delta.

That upgrade means the 2020 hurricane season had seven major hurricanes, rated Category 3 or higher, swirling through the Atlantic, tying 2005′s record for the most such storms.

The record 2020 season featured an unheard-of 30 named storms, exhausting the conventional alphabetized list of storms, while dipping farther into the supplementary Greek alphabet list than ever before.

With its revised rating, Zeta becomes the latest-landfalling major hurricane to ever hit the contiguous United States. According to the National Hurricane Center, the old record was set by the Tampa Bay Hurricane on Oct. 25, 1921.

Five of the last six storms in the 2020 Atlantic season reached Category 3 or higher.

The season ended with a bang when Category 5 Hurricane Iota struck the coast of Nicaragua barely 15 miles from where the devastating Hurricane Eta hit with Category 4 winds just two weeks before.

What the upgrade means

Initially believed to be a high-end Category 2 at landfall, the Hurricane Center used several techniques to reevaluate data and conclude that it was probably at marginal Category 3 strength, with maximum intensity estimated at 115 mph.

The upgrade, while inconsequential for warnings or advisories, is important for bookkeeping. National Hurricane Center records are instrumental in helping atmospheric scientists understand the climatology of tropical cyclones, as well as in the maintenance of a long-term data set that can point to trends in an era influenced by Earth’s changing climate.

Atmospheric scientists have pointed toward an uptick in the number of high-end hurricanes that have occurred, most likely linked to climate change.

The upgrade of Zeta is one of three significant findings from reanalysis that have prompted revisions to the 2020 season.

Postseason analysis found that Marco, a brief hurricane originally believed to have made landfall at tropical storm strength in Louisiana on Aug. 24, did not actually move ashore. While satellite imagery showed a swirl of clouds over land judged at the time to be the center of Marco’s circulation, wind and air pressure data indicate that the true center remained off the coast.

Since Marco didn’t cross the coastline, it reduces the number of 2020′s landfalling storms in the United States from 12 to 11, but the updated count is still a record for a single season.

The Hurricane Center’s reanalysis effort also concluded that Gamma, originally ranked a high-end tropical storm, was actually a hurricane when it made landfall on Mexico’s Yucatán Peninsula in early October. The Hurricane Center had originally stated that it was very close to hurricane status but kept it as a tropical storm as it came ashore.

Reviewing the data, they found maximum sustained winds had briefly met the 74 mph hurricane threshold. That increased 2020′s hurricane count to 14, twice the average number and one shy of 2005′s record for most in a single Atlantic season. Six of them, Hanna, Isaias, Laura, Sally, Delta and Zeta, made landfall in the United States.

Remembering Zeta

Zeta was born from a disturbance over the southwestern Caribbean that first manifest Oct. 19. By Oct. 24, a tropical depression formed south of Grand Cayman, and that same day it was designated a tropical storm as winds surpassed 39 mph.

Zeta became a hurricane 200 miles southeast of Cozumel, Mexico, early on Oct. 26, making landfall in Ciudad Chemuyil, Mexico, about 60 miles south of Cozumel, that night. The next morning, Zeta was a 65 mph tropical storm, but its emergence over the Gulf of Mexico meant it could quickly gather strength once again.

Passing over an environment characterized by abnormally warm sea surface temperatures and light upper-level winds, its rate of intensification was unprecedented in the Gulf of Mexico so late in the year.

Zeta slammed into southern Louisiana with maximum winds of 115 mph on the evening of Oct. 28, weakening as it moved inland and swallowing New Orleans in its eye.

A 105 mph gust was measured inside the eyewall in Golden Meadow, La., at 4:25 p.m. on Oct. 28, with sustained winds nearing 90 mph.

Zeta produced a storm surge of 9.5 feet at Old Fort Bayou in Ocean Springs, Miss., east of Biloxi Bay, with a 7.2-foot surge observed nearby in the neighborhood of West Biloxi.

Because Zeta was moving so quickly when it hit the Lower 48, its rainfall was tame compared with what it could have been. A broad four to six inches fell in southeastern Louisiana, southern Mississippi and southwest Alabama. Localized eight-inch totals occurred.