A scenario that might seem far-fetched — a hurricane evolving into a powerful post-tropical cyclone as it rolls along the East Coast all the way from Florida to Maine — has sprung to life in a new analysis of a real-world storm that struck 175 years ago.

Among other insights, the analysis of the Great Havana Hurricane of 1846 presents what appears to be the earliest evidence of a Category 5 strike on the young United States, as the storm took a worst-case route near Key West and largely demolished the thriving outpost.

If it happened today, the hurricane would not only inflict severe damage on the Florida Keys but also drench and thrash most of the biggest cities now on the Eastern Seaboard. Scholars estimate that it would produce at least $100 billion in damage and would rank among the most costly in U.S. history.

“Overall, the October 1846 hurricane caused the loss of hundreds of lives and incalculable property damage, with its unique inland track affecting many communities from the Caribbean to Canada,” said a study published this year in the Annals of the American Association of Geographers. Emily Cerrito led the study while completing her master’s degree at the University of South Florida, working with professor Jennifer Collins.

“Imagine the impact of this storm if it occurred today, considering all the population and infrastructure in those locations now,” Collins said in an email.

Collins and fellow co-author Cary Mock of the University of South Carolina produced a detailed study of an early-19th-century storm with uncommonly broad and intense impacts.

A perilous path across Cuba and Key West

The Great Havana Hurricane draws its name from the immense damage left by the storm in western Cuba as it moved north from the Caribbean. Cerrito and colleagues concluded that the hurricane was easily a Category 5 storm when it made landfall at Batabanó, about 25 miles from Havana on Cuba’s south coast, on Oct. 11, 1846. They estimate that peak sustained winds at Havana reached 162 mph.

“Although a comprehensive death toll for the 1846 hurricane is impossible to achieve, it is likely that hundreds of people were killed in Cuba as a direct result of the hurricane,” the authors said.

The storm went on to pass roughly 13 miles west of Key West, putting the island on the right-hand side of the hurricane, where the winds are typically strongest. A post-storm letter originally published in Washington’s Daily Union newspaper and cited in the new study refers to “a scene which defies descriptions. The houses in town (stone as well as wood) were torn to piecemeal and scattered away like chaff before the wind, rendering it dangerous to move about — which last was indeed impossible, as a foothold could not be maintained.”

Nearly all of the island’s 600 homes were unroofed, and about half were leveled by high winds combined with a storm surge that pushed as much as five feet of water across the island. Two lighthouses were demolished, and at least 50 deaths were reported. The pressure dropped to 944.8 millibars (about 27.90 inches) aboard the USS Perry, which was docked at Key West.

Given the veering of winds from northeast to southeast, the authors conclude that the storm’s eastern eyewall, or zone of most intense thunderstorms, passed near or over the island.

For both Cuba and Florida, “the 1846 hurricane is the first that can clearly be scientifically quantified as a Category 5 hurricane,” Mock said in an email.

Charging up the entire East Coast

After making landfall on the Big Bend of northwest Florida on Oct. 12, most likely as a Category 3 or stronger hurricane, the storm eventually got swept into a mid-latitude system that accelerated it along a course that put cities from Jacksonville to Portland, Maine, on its windier right-hand side.

The 1846 storm was among those analyzed in detail in the mid-19th century through pioneering maps hand-drawn by researchers William Redfield and William Reid. In the new study, drawing on much more comprehensive data and far more sophisticated mapping tools, “Emily Cerrito did a magnificent job taking it to the next level,” Mock said.

An expert in historical climatology, Mock contributed a wealth of data on the 1846 storm, including numerous newspaper clippings, diaries from plantations and instrumental records. “Many of these are archives that you cannot get online,” Mock said.

The storm’s path has no modern analogue. According to the study, the closest match could be a blend of Irma (2017) toward the south and Hazel (1954) toward the north. Based on those two storms, the authors concluded, damage could exceed that of Irma and Hazel combined if such a storm happened today, perhaps topping $100 billion.

Lourdes Avilés, a meteorology professor at Plymouth State University and author of “Taken by Storm, 1938: A Social and Meteorological History of the Great New England Hurricane,” emphasized the broad reach of the 1846 storm.

“This Havana storm passed through or near every metropolitan area along the Eastern Seaboard existing today,” Avilés said in an email. If such a storm were to recur, she added, “my gut feeling is that $100 billion worth of damages is a realistic estimate.”

As such, it would be among the most costly hurricanes on record in the United States. The existing top five are Katrina ($178.8 billion), Harvey ($138.8 billion), Maria ($99.9 billion), Sandy ($78.7 billion) and Ida ($64.5 billion).

A comparison with the 1821 Norfolk-Long Island Hurricane

Megan Linkin, a meteorologist and a senior underwriter in New York at Swiss Re Corporate Solutions, the commercial insurance arm of reinsurer Swiss Re, carried out a similar study on the 1821 Norfolk-Long Island Hurricane, which struck 200 years ago this September. It was another of the storms analyzed more than 150 years ago by Redfield.

Linkin concluded: “If the 1821 Hurricane were to happen today, it would cause 50 percent more damage than Sandy and potentially cause more than $100 billion in property losses stemming from storm surge and wind damage.”

The Norfolk-Long Island Hurricane produced major coastal flooding and widespread tree and structural damage along the East Coast. Storm surge reached downtown Norfolk along Water Street, a rare occurrence despite the street’s name. The storm tide in New York Harbor was at least 10 to 11 feet above average, perhaps as high as 13 feet, destroying some 300 feet of the Battery Park sea wall.

Because of extensive dredging, channeling and filling, as well as long-term sea level rise, the New York measurements from 1821 do not correlate directly with modern-day data collected at the Battery. However, the storm surge there was “definitely comparable with Sandy of 2012,” Mock said.

Linkin is not convinced that the newly reanalyzed 1846 storm would produce as much damage today as the 1821 storm would, but she said the 1846 event is worth further scrutiny, including a rigorous look at the buildings affected and the kinds of damage reported.

“Obviously they weren’t built to today’s standards,” Linkin said. “I think to really derive what the potential financial impact would be, you’d need to do something similar to what I did and others in the insurance industry have done: generate a wind-field and storm-surge inundation, and overlay it with today’s building stock and vulnerability.”

The 1846 hurricane serves as a sober reminder of the havoc tropical cyclones can cause across the heavily populated Eastern Seaboard, as well as an especially vivid illustration of how vulnerable the Florida Keys are — particularly Key West, the most populous of the islands and the most difficult to evacuate.

“I think these analyses of older hurricanes serve as a reminder that we can’t be complacent,” Linkin said. “It only takes one to track into a populated area to have a major impact, both financially and on the foundations of the community.”

After all, she observed, 2012 “wasn’t going to be a memorable hurricane season until Sandy came along.”

Bob Henson is a meteorologist and journalist based in Boulder, Colo. His books include “The Thinking Person’s Guide to Climate Change” and “Weather on the Air: A History of Broadcast Meteorology.”