An explosive September brought a spectacular end to an unusual streak of good luck that had kept major hurricanes away from U.S. shores for more than a decade, and the 2017 Atlantic hurricane season will now go down as the most expensive on record.
Totals are still being calculated, but early tabulations indicate that the U.S. suffered more than $200 billion worth of damage from 17 named storms during the season, which began June 1 and ends Thursday, November 30. That easily eclipses the previous record of about $159 billion, set during the summer of 2005, when Hurricane Katrina inflicted massive devastation on New Orleans. A record 28 named storms formed that year.
Most of this summer’s damage was caused by the infamous trio of Harvey, Irma, and Maria. Besides its winds, Harvey flooded Houston with more than four feet of rainfall as it made landfall August 25. Irma battered the Caribbean before coming ashore in the Florida Keys on September 10. And Maria destroyed homes and much of the infrastructure in Puerto Rico and inflicted a devastating disaster on the island when it came ashore on September 20.
Some estimates put Hurricane Harvey’s damage as high as $180 billion. The Bloomberg Business website recently reported more conservative estimates, pegging the combined total from Harvey, Irma, and Maria at about $202.6 billion.
In contrast, the infamous Hurricane Andrew that ravaged Florida in 1992 cost about $15.5 billion. The great Galveston hurricane of 1900 caused $20 million in damage (in 1900 dollars). Adjusted for inflation that's about $605 million in 2016 dollars. That's a sum that would likely be vastly higher today given the relatively higher costs of modern development.
A report on the 2017 hurricane season released Thursday by Colorado State University’s Tropical Meteorology Project notes several reasons why the 2017 season produced off-the-scale damages.
Unusually warm water in the area where hurricanes form in the Atlantic Ocean fueled the powerful storms, which formed when the peak of the season arrived in late August. Tropical storm activity had been about average until then.
Hurricanes draw their energy from seawater that has been heated to at least 80 degrees Fahrenheit. Early indications were that cooler temperatures would lead to a relatively quiet summer, but by late August the water had become unusually warm, despite the early season indicators, and that fueled the September eruption of hurricanes.
Asked why seawater temperatures didn’t follow the usual pattern this year, CSU meteorologist Phil Klotzbach said, “I don’t have a great answer for that as of yet.” He said atmospheric and ocean conditions elsewhere may have influenced the unusual conditions in the Atlantic.
Upper-level winds—known as wind shear—that can disrupt and weaken Atlantic hurricanes were low during the summer. This allowed the trio of expensive hurricanes to form, as well as a fourth, Hurricane Jose, whose 155-mph winds stayed offshore as it moved northward roughly parallel to the U.S. Atlantic coast.
Weather systems and steering currents that had fortuitously aligned to steer hurricanes away from U.S. shores since 2005 were not in place this year. This meant that hurricanes traveled farther west, and thus made U.S. landfalls, instead of turning harmlessly out to sea.
Scientists are wondering whether the summer of 2017 may carry some warning signals for future hurricane seasons. “It was indeed a remarkable season,” said meteorologist Kerry Emanuel of the Massachusetts Institute of Technology. But Emanuel noted that “it is hard to tease out a climate signal with statistical confidence” from the carnage of the 2017 season.
Still, in a recent article published in the Proceedings of the National Academy of Sciences, Emanuel said human-influenced climate change “is expected to lead to a greater incidence of high-intensity hurricanes” which, combined with rising sea level, will increase flooding from hurricane-driven storm surges. Hurricanes also could produce “substantially more” rainfall as the atmosphere and oceans become warmer, he said.
Meteorologist Jeff Masters of Weather Underground said 2017 could be a harbinger of seasons to come.
“The brutal 2017 season was an awful reminder of the huge hurricane vulnerability problem we face, and how unprepared we are for a potential future where the strongest storms get stronger and push their storm surges inland on top of steadily rising sea level,” Masters said.
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