Hurricane Irma Is on Track to Change the Course of Florida History

America's most vulnerable state is bracing for impact from an unnatural machine built for destroying whatever is in its path

skyline is seen as the outerbands of Hurricane Irma start to reach Florida on September 9, 2017 in Miami, Florida. Credit: Photo by Joe Raedle/Getty Images

Irma, the storm that meteorologists have been nervously tracking for days, is now on the doorstep of America's most vulnerable state. What's coming is unlike anything that's happened there before.

As of Saturday afternoon, Irma had begun a 36-hour trek northward off the coast of Cuba, where it made landfall as a Category 5 hurricane earlier in the day. By the time it reaches Florida, it's expected to restrengthen and grow in size as it travels over the abnormally warm Gulf Stream – high-octane fuel for hurricanes.

Florida can't possibly defend itself against a hurricane like Irma. The storm is already a behemoth: Its winds pack nearly 100 terajoules of energy – more than the atomic bomb released over Hiroshima, if it were continuously exploding. And, in fact, that's a good way to think about Irma: An unnatural machine built for destroying whatever is in its path.

Irma's outsized energy output means its destructive potential is more than three times that of last month's Hurricane Harvey, and more than six times that of 1992's Hurricane Andrew, the last Category 5 hurricane to make landfall in the United States. The combination of its large size and strong winds is giving Irma a tremendous ability to push ocean water shoreward, what meteorologists call storm surge.

Nearly 7 million people have been ordered to leave their homes across Florida – the largest mass evacuation in U.S. history. More than half a million of those are in the Tampa area, the region of the country most prone to a colossal storm surge disaster.

Historically, storm surge is the deadliest component of any hurricane, and there's a good chance it will be the legacy of Irma, too. Problem is, cities like Tampa – now squarely in Irma's direct path – just aren't ready for a storm like this. The last major hurricane to hit Tampa was way back in 1921, when the city had just 50,000 residents. Now, the area has more than 3 million, and is among the fastest-growing cities in the country.

In 2010, with the help of FEMA, officials in Tampa conducted a trial run for the worst-case scenario, called Project Phoenix: A Category 5 hurricane hitting the region head-on. The exercise, using a fictitious storm called "Hurricane Phoenix", predicted a storm surge within Tampa Bay of nearly 30 feet – enough to utterly overwhelm the city. A half-million homes would be destroyed, and as many as two million people would have to seek medical care. It would be the biggest natural disaster in American history.

In May, just before the start of this year's hurricane season, a new modeling effort showed that Project Phoenix underestimated the worst-case risk by as much as six feet. And that's not factoring in sea level rise, which could bring another six feet in just a few decades.

For a state that would rather ignore climate change, the next two days will change the course of Florida's history. What comes next will mean the difference between disaster and endurance during future hurricanes.