In June, residents across southeast Louisiana got a familiar warning: A storm was coming — time to check generators, supplies and evacuation plans.
Tropical Storm Cindy was moving through the Gulf of Mexico, an early-season cyclone aimed at the Louisiana coast.
Though Cindy made landfall with more whimper than wallop, it set the stage for an anxious season of tropics-watching, as the Atlantic Ocean churned out 17 named storms, five more than average, including six storms that reached Category 3 or above.
The season that officially closed Thursday was the busiest Atlantic hurricane season since 2005, and it included the busiest single month on record.
Three major storms were the headliners of 2017: Harvey swamped large sections of the Houston area; Irma raked Florida, especially the Keys; and Maria left Puerto Rico in shambles. Rarely before had three major storms — Category 3 or above — made landfall in the United States in one year since the start of record-keeping in 1851.
Harvey ended an 11-year streak in which no Category 3 or higher hurricane had hit the U.S. coast, according to Barry Keim, Louisiana's state climatologist. The last major hurricane to hit the U.S. was Wilma in late 2005, the same year as Katrina and Rita. The 11-year streak was by far the longest such streak recorded.
The numbers from 2017's major storms are staggering: more than $200 billion in damages, 60 inches of rain produced by Harvey, and 185-mph winds in Irma. But beyond those attention- grabbing figures, 2017 really was "one for the record books," according to Ken Graham, a forecaster with the National Weather Service's New Orleans office.
"September was the most active month on record" across the globe, he said. "Irma was the strongest Atlantic storm on record that was outside the Gulf or Caribbean."
The conditions that led to September's activity were straightforward: warm Atlantic waters combined with no wind shear, which is normally produced by an El Niño in the Pacific, Graham said.
Those conditions weren't foreseen when the season began, according to Phil Klotzbach, a hurricane researcher at Colorado State University.
"Generally, when you have a cold north Atlantic in March, it keeps activity down," he said. This year, the northern Atlantic started cold but "warmed anomalously" after that.
Forecasters also expected a weak or moderate El Niño, which didn't form, he said. "We had background conditions that helped (storms) ramp up but also steering so that they hit land," Klotzbach said.
Graham said those conditions made the storms not only more numerous but also stronger.
"The water was warm; there was no wind shear to be found; there was nothing to stop them from getting real strong," he said. "In a lot of cases, getting strong quickly."
Louisiana largely dodged the storms' collective wrath. One exception was the southwest corner of the state, where Harvey, after having laid waste to much of America's fourth-largest city, came ashore in a second landfall as a tropical storm.
Other storms nicked the state: Cindy created some problems along Louisiana's coastal areas but caused more damage in Mississippi and Alabama, and the late-season Nate was too fast-moving and too buffered by dry air on its west side to do much damage to Louisiana after it made landfall near the mouth of the Mississippi River.
"It was a lot of near misses," said Mike Steele, a spokesman for the Governor's Office of Homeland Security and Emergency Preparedness. "A couple of storms had us in the bull's-eye" but ended up missing the state by mere miles, he added.
The National Weather Service's Graham agreed.
"I think it's just the way it worked out," he said. "You move those storms 30 miles in different directions, and the impacts are significantly different." One gauge in coastal Mississippi got 12.2 inches of rain in during one storm while another one seven miles away got 3.5 inches, he said.
It's still too early to offer a forecast for next year. Even though we are in what would be considered an "active cycle," it's hard to tell how that will play out in individual years, Keim said. The U.S. was in an active phase from 1925 until 1965, he said, followed by a 30-year quiet phase.
"Most of the seasons were somewhat below normal," he said. "Camille (in 1969) and Andrew (1992) were the exceptions" during that period, he added.
Then, in 1995, sea temperatures rose, leading to another active phase, but that doesn't mean "every season is going to be incredibly active," he said.
Keim also said it is too early to confidently blame climate change for the storms, but he said there is a "general consensus" among scientists that climate change may contribute to the intensity of the storms.
"These are the big questions, that nobody really knows the answer to," he said, noting that before 2017, Louisiana had gone four years without a storm making landfall. This year, it had three, even though none was a major storm.
"Maybe that four years was just a pause," he said.