Written by Elena Shao, Nadja Popovich and Mira Rojanasakul
New data from NASA reveals how warm ocean waters in the Gulf of Mexico fueled Hurricane Ian to become one of the most powerful storms to strike the United States in the past decade.
Sea surface temperatures were especially warm off Florida’s southwest coast, allowing the storm to pick up energy just before crashing into the state north of Fort Myers.
The storm brought fierce winds, unrelenting rains and catastrophic flooding to southwest Florida. As it moved inland, it lost power and was downgraded to a tropical storm, but grew into a hurricane again as it traveled across the warm Atlantic toward South Carolina.
Storms usually weaken as they move over land and lose access to their main source of moisture and energy.
Hurricane Ian was able to, over the course of its path, pull a lot of energy out of the ocean, which could have sustained it for longer than normal, said Christopher Slocum, a physical scientist at the National Oceanic and Atmospheric Administration.
September is the peak of hurricane season, spurred by temperatures in the Gulf that are warmer than at other times of the year, experts say. The climate phenomenon known as La Niña has also contributed to more favorable conditions for hurricanes in the North Atlantic over the past three years.
However, waters off the coast were also 2 to 3 degrees Fahrenheit warmer than usual for this time of year, according to preliminary data from NASA.
And a few degrees can make a huge difference, said Karthik Balaguru, a climate scientist at Pacific Northwest National Laboratory, because it provides extra energy for a storm.
Unlike with land or the atmosphere, “it’s very difficult to warm the ocean,” Balaguru said. A large amount of heat had to have been absorbed by the ocean just to raise temperatures by a small fraction of a degree, he said.
More than 90% of the excess heat from human-caused global warming over the past 50 years has been absorbed by the oceans, and a majority of it is stored in the top few hundred meters.
Scientists say that while climate change has not necessarily increased the number of hurricanes, it has made them more powerful, as warmer ocean waters strengthen and sustain those storms. The proportion of the most severe storms — Categories 4 and 5 — has increased since 1980, when satellite imagery began reliably tracking hurricanes.
As the climate warms, more storms are also undergoing rapid intensification, which describes an increase of at least 35 mph in the maximum sustained winds over a 24-hour period. Ian rapidly intensified multiple times, as did a number of the past decade’s most powerful Atlantic storms. Hurricane Harvey in 2017 surged from a Category 1 hurricane to a Category 4 overnight. In 2021, Ida strengthened from a Category 1 to a near-Category 5 in less than 24 hours.
A warmer climate also allows hurricanes to unleash more rain, a consequence of an atmosphere that, with each degree Celsius of warming, can hold about 7% more water vapor that then gets released as precipitation. In addition, storm surges are riding on top of elevated sea levels, which can worsen coastal flooding.
Wetter, more intense hurricanes can have devastating consequences for the communities they strike, said Kristie L. Ebi, a professor in the University of Washington’s Center for Health and the Global Environment. For the most part, the most damage to life and property both during a hurricane and its aftermath comes from the flooding, not the winds, she said.