How ‘Bermuda High’ Threw Irma and Damage Estimates Off Course

Twenty miles may have made a $150 billion difference.

Estimates for the damage Hurricane Irma would inflict on Florida kept mounting as it made its devastating sweep across the Caribbean. It was poised to be the costliest U.S. storm on record. Then something called the Bermuda High intervened and tripped it up.

“We got very lucky,” said Jeff Masters, co-founder of Weather Underground in Ann Arbor, Michigan. If Irma had passed 20 miles west of Marco Island instead of striking it on Sunday, “the damage would have been astronomical.”

By one estimate, the total cost dropped to about $50 billion Monday from $200 billion over the weekend. The state escaped the worst because Irma’s powerful eye shifted westward, away from the biggest population center of sprawling Miami-Dade County.

The credit goes to the Bermuda High, which acts like a sort of traffic cop for the tropical North Atlantic Ocean. The circular system hovering over Bermuda jostled Irma onto northern Cuba Saturday, where being over land sapped it of some power, and then around the tip of the Florida peninsula, cutting down on storm surge damage on both coasts of the state.

“The Bermuda High is finite and it has an edge, which was right over Key West,” Masters said. Irma caught the edge and turned north.

For 10 days, computer-forecast models had struggled with how the high was going to push Irma around and when it was going to stop, said Peter Sousounis, director of meteorology at AIR Worldwide. “I have never watched a forecast more carefully than Irma. I was very surprised not by how one model was going back and forth — but by how all the models were going back and forth.”

In the end, Irma landed on the Florida Keys as a Category 4 hurricane with 130-mile (209 kilometers) per hour winds, then as a Category 3 at Marco Island. It reached the Tampa Bay area as a Category 2. By contrast, Hurricane Andrew in 1992 plowed into the east side of Florida as a Category 5.

“With Irma, little wobbles made a huge difference,”said Chuck Watson, a disaster modeler with Enki Research in Savannah, Georgia. With a tightly-wound storm like Andrew coming straight into the state, “a 30-mile wobble isn’t going to matter.”

Still, when it comes to damage, “Irma may bump Andrew,” Watson said. The company’s most recent estimate is for $49.5 billion in Irma costs for Florida; Andrew’s were an inflation-adjusted $47.8 billion. White House Homeland Security Adviser Tom Bossert said Monday that Jacksonville was suffering what may amount to the worst flooding in a century, citing reports.

The price tag for Hurricane Harvey, which struck southeastern Texas on Aug. 25, could end up between $65 billion to $75 billion, according to AIR Worldwide, a Verisk Analytics risk modeler based in Boston.

The top spots at the moment are held by 2005’s Hurricane Katrina, at $160 billion, and 2012’s Superstorm Sandy, at $70.2 billion, according to a list compiled by the U.S. National Centers for Environmental Information.

Those are modern storms. Simulations based on the paths and powers of some that rammed the U.S. 100 or more years ago show they were far more disastrous, or would be if they arrived today when the population is much more dense and there is far more, and far more expensive, property to destroy.

One hurricane that raked the U.S. East Coast in 1893 was so furious the impact could have added up to $1 trillion. “They haven’t really happened in our modern economy,” Watson said, adding it’s only a matter of time. “We have so much stuff and so much infrastructure. Leave all the arguments about climate change aside; we are rapidly moving into that era where we are going to be seeing $50 billion, $100 billion storms, and I will not be surprised when we get to $300 billion.”

Now meteorologists are watching Hurricane Jose churn in a circle north of the Leeward Islands. Sousounis said computer models are struggling to predict whether it will pass harmlessly out to sea or strike Cape Cod at the end of Massachusetts. Jose won’t give up the answer for more than a week.