As Hurricane Irma nears the Florida coast, the tension on the peninsula is palpable. One of the largest evacuations in U.S. history is underway, and the storm is still strengthening. After days of anticipation and worry, one thing is now certain: Someone, somewhere is going to get hit hard.
Irma has been tearing through the record books in recent days at a breakneck pace—at this point, it’s already singlehandedly produced more total wind energy output than 14 entire Atlantic hurricane seasons. For the rest of its lifetime, Irma will be traversing some of the warmest ocean waters on the planet.
For those watching from Florida, Irma’s unique expected path—a right hook up from the Cuban coast—is complicating matters. Once Irma’s course bends northward, it will align itself more or less lengthways with the Florida peninsula, meaning even at this late hour, almost anywhere in the state could still get a direct hit. The problem is, meteorologists still don’t know exactly when the northward turn will happen.
The overnight models haven’t helped clarify things much: Over the past 24 hours, there’s been a significant westward shift, lessening the risk to East Coast cities like Miami and Fort Lauderdale, and increasing the risk for West Coast cities like Naples and Tampa.
Florida’s midsection is just 110 miles wide, and hurricane force winds extend out about 60 miles from Irma’s center, so a shift in track by just 50 miles to the east or west (the average two-day track forecast error for the National Hurricane Center) could be the difference between catastrophic destruction and just a really windy day, depending on where you are and where exactly the center comes ashore.
Here are the three leading scenarios for where Irma is headed next, as of Saturday:
Scenario 1: Irma travels up the East Coast, including a direct hit on Miami.
For days, this scenario looked like the most likely one. Most of the national media initially set up their live shots in Miami, and insurers began to raise the alarm of a potential $200 billion disaster—a direct hit on southeast Florida by a Category 5 hurricane would quickly become the worst disaster in American history, surpassing the damage wrought by either Katrina or Harvey.
About 85 percent of Miami-Dade County lies less than 10 feet above sea level, and Irma’s storm surge, if it comes at the right angle during high tide, could match that mark. On top of the surge, wind-driven waves up to 45 feet high could loom just offshore, significantly eroding barrier islands like Miami Beach. The neighborhoods that aren’t washed into the ocean could be flattened by Irma’s tremendous winds.
Thankfully, that scenario became slightly less likely on Friday, owing to an unexpected westward jog in Irma’s track through the southern Bahamas. A high-pressure center over the central Atlantic gave a bit stronger nudge to the storm’s circulation, which just goes to show how delicate the forecast is and how much is on the line.
The National Weather Service in Miami isn’t taking any chances, however. On Friday, they sent out a chilling warning that "locations may be uninhabitable for weeks or months" in the aftermath of a direct hit.
Scenario 2: Irma makes landfall in the upper Florida Keys, then moves up the center of Florida.
Although a path straight up the middle of Florida seems like a terrible thing to hope for, it might actually be Florida’s best chance of limiting the scale of Irma’s destruction. The Everglades are a natural defense against storms, and if Irma hits them head on, much of the surge and wave energy could be dissipated.
Still, for parts of the upper Keys, Irma would be a catastrophe, with localized rise in ocean levels of 14 to 16 feet. Many of the Keys would be temporarily overwashed, and could be cut off. In an interview on Friday, the acting director of the National Hurricane Center, Ed Rappaport, said “it's not clear that it's a survivable situation for anybody that is still there in the Keys.”
Once Irma moves inland, it could kick off a potentially disastrous inland flood at Lake Okeechobee. The U.S. Army Corps of Engineers warned on Friday that Irma could create a seiche in the lake—an extreme sloshing of water that may threaten local levees and dikes. This happened in a 1928 hurricane, leading to hundreds of deaths. Mandatory evacuations for the lakeshore have already been issued as a precaution.
Scenario 3: Irma makes landfall near Key West, then travels up the West Coast of Florida.
For all the attention placed on Miami, it’s actually the Tampa Bay area that is America’s most vulnerable when it comes to storm surge from a major hurricane. In 2010, with the help of FEMA, the city conducted an extensive worst-case scenario drill with a Category 5 “Hurricane Phoenix” making landfall in the region. The result was an unimaginable tragedy: Half a million homes ruined and a death toll of more than 2,000—greater than Hurricane Katrina.
Tampa’s last direct hit by a Category 3 or higher storm was way back in 1921, when the city had just 50,000 residents. Now, the metro population is more than 3 million. The Hurricane Phoenix simulation found that the unique geography of the bay would concentrate and enhance the storm surge, pushing it to nearly 30 feet in some areas.
Unfortunately, the odds are increasing that Irma could be something like Hurricane Phoenix. Irma is now expected to spend more time over the water after leaving Cuba, potentially boosting its strength and increasing the risk to Tampa. Since Irma is so large, most of Florida would experience hurricane-force winds, too.