Six months ago, forecasters predicted the 2017 hurricane season would be just below average.
They were wrong.
The season, which ends today, far exceeded expectations, delivering three landmark storms to the United States and Caribbean and, by some measurements, adding up to a top-10 year. And it was the second year in a row, after an unprecedented 11-season lull for Florida, that the Sunshine State was battered by a hurricane.
"It was certainly one of the most active seasons we've seen in a long time," said Michael Bell, a professor in Colorado State University's Department of Atmospheric Science and a co-author of the university's hurricane season summary. "This is certainly one to remember."
What just happened? And what does it portend?
That's not so clear.
Scientists initially struggled to forecast the 2017 season. Some had expected at least mild El Niño conditions, or warmer than usual water temperatures in the tropical Pacific Ocean. So, forecasters had initially predicted a less active hurricane season. That's because El Niño tends to produce increased wind shear that helps rip Atlantic storms apart or weaken them before they become major cyclones.
Turns out El Niño never really materialized. Instead, tropical Pacific water temperatures were colder than average heading into the heart of the season, approaching what is known as La Niña conditions ripe for storm development, Bell said. That, combined with relatively warm Atlantic and Gulf of Mexico waters, which fuel hurricanes, proved devastating.
How bad was it?
Hurricane Harvey appeared to be weakening over the Yucatán peninsula when it re-emerged over the toasty gulf and rapidly intensified. It devastated the Corpus Christi area of the Texas coast where it made landfall as a Category 4 storm Aug. 25 then stalled, dumping record rain. Sixty inches fell in some areas, leaving parts of Houston under water for weeks.
At least 75 people died as a result of the storm, according to the Houston Chronicle. Ball State University estimates damages at up to $200 billion, which would make it the costliest hurricane ever.
Then came Irma less than two weeks later, hitting all kinds of marks: Strongest hurricane to form so far east in the Atlantic; one of only five storms to hit 185 mph wind speeds, according to the National Weather Service; the only storm to sustain that strength for 37 hours straight, according to Bell. After battering parts of the Caribbean, the storm skimmed Cuba, a blessing for Florida, said Phil Klotzbach, a hurricane research scientist and Bell's colleague at CSU, by email.
We've made it to the final day of the 2017 #Hurricane Season! Check out https://t.co/rkmLFVCELL for a summary of this very active season! #flwx pic.twitter.com/uezPXBdMLN— NWS Tampa Bay (@NWSTampaBay) November 30, 2017
A weakened Irma still demolished parts of the Florida Keys. At one point predicted to hit Tampa Bay, it instead made landfall near less-populated Marco Island Sept. 10 as a Category 4 storm. An enormous hurricane, it caused flooding on both Florida coasts, toppled trees and knocked out power for most of the state. It has been blamed for up to 134 deaths, including at least 75 in Florida, according to the Miami Herald. Damages could reach in the tens of billions.
As a third act, there was Maria, which laid waste to Puerto Rico as a Category 4 storm Sept. 20, rendering much of the U.S. territory uninhabitable and leaving many of its 3.7 million residents homeless. It was the first Category 4 hurricane to make landfall there since 1932, according to the Colorado State report.
Most buildings were damaged on the already impoverished island, and many of its residents are still without power or potable water and are likely to remain so into next year. Emergency managers have reported a death toll of 55, though a CNN report cast doubt on that number, saying it could be hundreds more. Damages are expected in the tens of billions.
Official death tolls and damage estimates for the season from the National Hurricane Center will likely not be ready before February, officials there said. It was the first time on record two Category 4 storms made landfall along the continental U.S. in the same year, and Irma was the first storm since Charley in 2004 to hit Florida with Category 4 intensity.
Will my next insurance bill make me cry?
The state has seen $5.9 billion in insured losses as of Nov. 13, according to the Florida Office of Insurance Regulation, almost entirely due to Irma. Just last year, the agency reported $1.18 billion in insured losses from Hurricane Matthew.
It brought significant damage to the Keys and areas such as Naples. But the overall damage totals were significantly lower than projected.
Small, untested insurers — a worry for some — appear to have been relatively prepared with enough money to cover claims. The Florida Hurricane Catastrophe Fund, which insurers buy into as a backstop, has plenty of cash on hand to cover losses.
"Insurance companies did not have huge payouts because the storm was not as damaging as they thought," said Lynne McChristian, spokeswoman for the Insurance Information Institute.
Consumers aren't likely to feel any extra pinch from this hurricane season any time soon in terms of hiked rates. Insurance companies, which are required to file their rates with state regulators, have already filed for 2018, locking in next year's prices.
A slight bump could come in 2019.
Is this the future?
Don't blame climate change for this year's activity just yet, Bell said.
"There's still a lot of uncertainly about how hurricane activity will respond to the future," he said. "The current consensus is that hurricanes could be more intense but less frequent in a warming climate."
Even though hurricanes would benefit from warming ocean temperatures, other factors, like wind shear, also affect hurricane development and growth. And, Bell said, it's still uncertain exactly how a warming climate could affect those other factors.
And what really matters for people is landfall. And so far, Bell said, there has not been any long-term increases in the number of hurricane landfalls.