Animated satellite imagery of a hurricane moving toward Florida from the Antilles — Hurricane Dorian on its path toward Florida. Source: NOAA

Hurricane Seasons Are Getting More Severe

By Lauren Leatherby, Mira Rojanasakul and Eric Roston

Published: August 30, 2019, 2:00 PM EDT | Updated: September 1, 2019, 10:00 PM EDT

Hurricane Dorian, the first major hurricane expected to make U.S. landfall in 2019, has become a Category 5 storm. Dorian brought 185 mile-per-hour winds and 10 to 15 inches of rain as it came ashore in the Bahamas; Florida’s fate remains uncertain. The storm may be the first of multiple powerful hurricanes this year: Earlier this month, the National Oceanic and Atmospheric Administration increased its chances of an above-normal hurricane season for 2019.

The last two decades have seen some of the most powerful and destructive hurricane seasons on record, a function of coastal development, warmer water, wetter air, higher seas and storms just being storms.

Scientists weigh in on the topic of climate change and hurricanes cautiously, largely because they’re relatively rare events (compared with, say, minute-by-minute temperature changes), and the historical record is spottier the further back they go. They make specific statements where they can: Water warmed up by human greenhouse gas emissions makes hurricanes stronger and rainier. Atlantic hurricane activity has grown since 1970, in part from cuts in air pollution that removed storm-dulling sulfur and other particles from the atmosphere. The intensity of recent storms like Harvey, Irma and Jose is what they expect from a warming world.

The U.S. eluded a major hurricane (Category 3 or above) strike between 2005 and 2017, the longest gap on record going back to 1851. That doesn’t mean big Atlantic storms didn’t spin elsewhere during that time. Since 2005, three hurricane seasons in the North Atlantic had multiple Category 5 storms. That only happened one other time in the last century.

Still, hurricane seasons long ago came with their own devastating storms. And every so often a series of seasons can be particularly brutal. Four of the top 10 years for major storms occurred from 1950 to 1964, according to Weather Underground.

Hurricanes are also growing much more costly as storms become slower and wetter and as people move to coastal areas. Population density in coastal counties along the Gulf of Mexico nearly tripled between 1960 and 2018 and doubled in counties along the Atlantic Coast.

The forward speed at which hurricanes move slowed 10% globally between 1949 and 2016, according to a 2018 study in Nature, which pointed to warming-induced changes in atmospheric circulation. Slower-moving storms mean that hurricanes can linger wherever they hit, which cause staggering rainfall totals. Flood damage—rather than damage from high winds—is often the highest cost of hurricanes. Hurricane Harvey was a prime example: The slow-moving storm battered the country’s fourth-largest city for days, dropping more rain than any other storm system in history. It’s the country’s second most-costly disaster.

Florida is preparing for Dorian amid a partisan fight in Washington over disaster relief. At stake is $271 million in funding for several Homeland Security Department agencies, about 57% of which had been slated for the Federal Emergency Management Agency’s Disaster Relief Fund. The Trump administration wants to transfer the funds to a program that returns asylum-seekers to Mexico while they await immigration court dates, according to a document obtained by Bloomberg Government.

The disputed relief fund sum is a lot of money but small relative to early estimates of Dorian’s potential damage, and to the costs associated with the biggest storms of the past several years. Hurricane Michael hit Florida’s panhandle last year as a Category 5 storm and caused $10 billion in insured losses. With NOAA predicting two to four hurricanes at category 3 or stronger this season, Dorian may not be the last damaging storm to wreak havoc on the North Atlantic this year.

Hurricane Seasons Are Getting More Severe

Hurricanes by decade

Hurricanes are getting more costly

FEMA Disaster Relief Fund balance