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Why Hurricane Irma wasn’t far worse, and how close it came to catastrophe

Hurricane Irma has wrought havoc all over Florida and is no slouch of a storm. But, while extremely costly, it may not rank among the state’s worst-ever hurricane disasters, as had been feared.

Leading up to its back-to-back landfalls in the Florida Keys and on Marco Island, several twists of fortune eased the pain the storm inflicted on the state. And only slight deviations would have made the storm’s outcome much more severe.

The first stroke of good luck for Florida occurred when the center of a Category 5 Irma scraped along Cuba’s north coast. This, of course, turned into Cuba’s misfortune. But Irma’s interaction with land weakened the storm from a potentially catastrophic Category 5 to a Category 3.

While Irma recovered some of its strength and made landfall in the Keys as a low-end Category 4, it was not the same behemoth it was before its Cuban encounter.

Key West then caught the next lucky break. While the storm’s vicious eyewall battered the island and winds gusted over 90 mph, the most intense right-front quadrant of the eyewall, where wind and storm surge are maximized, passed just to its east.

Dissecting the parts of a hurricane

The Florida Keys’ far less developed zone from Sugarloaf Key to Marathon caught the brunt of the eyewall’s wind and surge:

When Irma approached the Florida peninsula, there was no “good” course for it to follow. Devastation was guaranteed from a storm so big and so strong (attested to by the 6 million-plus power outages), but the track it ultimately pursued was better than some alternatives.

The dangerous right-front quadrant with the worst winds and biggest surge targeted the stretch from Everglades City to Marco Island, a less populated zone than many others.

If the right-front quadrant had instead targeted Miami, for example, the storm surge disaster would have been unimaginably bad — akin to the worst-case scenario we wrote about before the storm.

“The storm surge flooding in Miami [on Sunday] is a mere fraction of what would have happened if the core of #Irma had been farther east,” tweeted Rick Knabb, a hurricane expert at the Weather Channel and former director of the National Hurricane Center.

Graphic: See the storm surge and its impact

Finally, when Irma’s journey inland over the Florida peninsula near Naples and the eyewall’s trajectory over land helped seal the deal in terms of reduced impact. If the storm center had stayed over the warm Gulf of Mexico on its way up the coast, it would have maintained its power longer, and its right-front quadrant could have battered more population centers, including the very vulnerable Tampa.

Ultimately, Key West, Miami and Tampa — all perilously exposed to hurricanes due to their geography, population and infrastructure — just missed a much more damaging experience from Irma.

Before the storm, many trusted forecasters warned that Irma could be one of the most infamous storms in history. Did they go too far in sounding the alarm about this storm? Given all of these near misses and the fact that only the most subtle changes in the storm’s evolution would have caused much more horrifying scenes, the answer is probably no.

For better or worse, in predicting this storm, forecasters had to emphasize the worst-case scenarios. When decisions had to be made about evacuations late last week, for example, a direct landfall in South Florida seemed plausible.

Then, forecasts couldn’t pin down whether the eye of Irma would scrape across Cuba’s north coast or narrowly remain over open water, which made the difference between 130 mph winds and 160 mph winds or stronger.

Lastly, when the storm track shifted to Florida’s west side, knowing exactly where the storm would come ashore — which had massive implications — couldn’t be pinned down.

President Trump, before a winter storm that underperformed expectations in March, said something often true but inconvenient about storm forecasting: “Let’s hope it’s not going to be as bad as some people are predicting. Usually it isn’t.”

Irma’s track forecast was adequate, but there’s significant room for improvement

Until forecasts are good enough that we can pinpoint the enormously consequential shifts and wobbles, forecasters will continue to err on the side of caution. And, in many, maybe most cases, the outcome won’t be as severe as feared. But given what’s at stake if a worst-case scenario materializes and potential victims need to be ready, forecasters have a serious obligation to communicate the possibility.