It’s been more than eight years since the United States has been hit by a hurricane with winds strong enough to make it a Category 3 — what’s officially considered a “major” storm.
The last time a major hurricane struck was in 2005, the year both Katrina and Rita battered the Gulf South, making the current drought the longest since record keeping began in the 1880s.
The previous record for time without a major hurricane making landfall was five years, which last occurred from 1910 to 1914.
The reason, experts say, is a combination of a particular weather pattern and luck — with lots of the latter.
“We’ve been very lucky,” said Phil Klotzbach, a research scientist with the Tropical Meteorology Project at Colorado State University.
He said another factor has been a low-pressure area parked along the East Coast for much of the past eight years that helps push storms northward, where they get caught up in the jet stream and pushed back out to sea.
“It’s not just blind luck. There have been atmospheric conditions,” he said.
But Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, doesn’t attach any significance to the lack of major hurricanes hitting the United States since 2005. The fact that it gets mentioned at all is a product of a human evolutionary need to recognize patterns, he said.
“We often see patterns that don’t exist. That’s the way our minds work,” Emanuel said. “Often it turns out it’s just chance.”
The 2004 and 2005 storm seasons were hyperactive: The Atlantic spawned 13 major hurricanes in those two years, and seven of them made landfall in the United States, Klotzbach said. Since then, 22 major hurricanes have formed but none has hit the United States. If the long-term average had held, at least seven of those storms would have struck the U.S.
As this year’s hurricane season opens today, scientists and emergency preparedness officials warn that the public tends to give too much weight to the category of a storm when assessing the threat it poses. Wind speed — the determining factor for the category of a storm using the Saffir-Simpson scale — doesn’t fully account for the damage a hurricane can do.
How fast a hurricane is moving, the direction it takes and the strength it reaches while offshore all contribute to the size of its surge, which is the most dangerous aspect of a storm. And the torrential rain that can accompany a hurricane creates its own flooding hazards. None of those factors depends strictly on wind speed.
In 2012, Hurricane Isaac approached Louisiana’s coast as a Category 1 storm. It was a large, slow-moving storm that seemed to linger on the coastline forever before meandering north, flooding much of south Louisiana.
Likewise, Hurricane Gustav in 2008 wasn’t a “major” hurricane, but it still proved deadly. In Baton Rouge, the storm felled thousands of trees, killed two people and destroyed homes and businesses throughout the area. Hundreds of thousands of people were left without power, many for weeks.
“It doesn’t matter what your definition of major storm is, for Baton Rouge, Gustav had major impacts,” said Ken Graham, meteorologist in charge at the National Weather Service office in Slidell.
The shift away from focusing so intently on wind speed has occurred in emergency management and first-responder circles, he said.
“But we have to get the general public to really understand it,” Graham said. “It doesn’t have to be defined as a major storm to have a major impact.”
On average, southeast Louisiana is affected by a tropical storm every two years, a hurricane every four years and a major hurricane every 12 years, Graham said. Those are long-term averages, so gaps in activity threaten to make people complacent, he noted.
“It doesn’t take much for people to forget a major storm,” Graham said.
State Climatologist Barry Keim said anyone who has lived in south Louisiana for a while isn’t likely to forget the lessons of the 2005 hurricane season. And in the years since then, storms like Gustav, Ike and Isaac have shown how destructive lower-category hurricanes can be, he added.
“We’ve had enough activity here that people are aware of the hazard,” Keim said.
However, Guy Laigast, director of Plaquemines Parish’s Office of Homeland Security and Emergency Preparedness, said complacency is a concern even for people who have experienced a past storm if they think the current threat isn’t a big one.
During the Category 1 Hurricane Isaac in 2012, he said, the parish knew there was going to be flooding and issued a mandatory evacuation order, “but people didn’t do it.”
As a result, about as many lives were lost as in Katrina, he said.
“Here comes little Isaac, and we had the same number of people perish,” Laigast said. “That’s just not right.”
Most of the deaths from tropical weather systems involve water, not wind, which is something he said emergency officials want people in coastal communities to understand.
“Isaac was a big wake-up for our folks,” Laigast said.
Follow Amy Wold on Twitter, @awold10.