Isaias made landfall as a Category 2 hurricane near Destin, Florida, last week with winds of up to 105 miles per hour. The system produced flooding, damaging winds and isolated tornadoes across the Southeast with 8 people losing their lives in Florida and Alabama.
October hurricanes are not unusual. What is unusual?
How warm the Gulf waters are this fall.
Unseasonable October warmth
A new analysis from the non-profit Climate Central suggests abnormally warm waters in the Gulf helped to strengthen Isaias into a major hurricane. Though Isaias weakened quickly after landfall, the hurricane experienced rapid intensification twice as it moved through the Gulf. Researchers found more than 90% of warming in the Gulf this summer can be attributed to human-influenced climate change.
Water temperatures in the Gulf were as high as 88 degrees Fahrenheit when Isaias moved through – nearly 2.5 degrees higher than water temperatures would be in a world without human-caused warming.
The water temperatures were also above average for October and more reminiscent of temperatures in August. Oceans are very efficient at absorbing heat. So, when humans emit more heat-trapping carbon pollution into the atmosphere, that can lead to above average sea surface temperatures.
Climate Central meteorologist Daniel Gilford said the abnormally warm water helped to supercharge Isaias. He said a hurricane is like a car engine and the warm Gulf waters like gasoline.
“So it takes that fuel, it gobbles it up, and it converts that fuel into kinetic energy in the form of winds,” Gilford said. “So as you increase the amount of temperature, you're increasing the amount of fuel that the storm can consume.”
Overcoming El Niño
Isaias was the first hurricane to form in the Atlantic basin this year. Strong El Niños often suppress tropical activity in the Atlantic because they create more “wind shear” – a difference in wind speed or direction with height. Strong winds higher up in the atmosphere can rip a storm apart.
Gilford said to think of wind shear’s impact on a hurricane like a spinning toy top.
“If you bump the top of that top, it will start to wobble and then eventually fall over,” Gilford said. “More wind at the top sort of pushes over the storm. And then the storm starts to wobble and actually tear itself apart.”
Isaias began to weaken from increasing wind shear shortly before landfall. But prior to its arrival in the Florida Panhandle, the bathwater-like temperatures in the Gulf helped Isaias to overcome the wind shear. At its strongest, Isaias was a Category 3 hurricane with peak winds at 120 miles per hour.
The research also suggests human-caused climate change made Isaias winds speeds increase by 7 miles per hour. Gilford said even that small amount can make storms more destructive, especially in vulnerable communities along the Gulf Coast.
“Our analysis shows that even when you account for that El Niño, you still have this supercharged warming from climate change, which drove changes in the hurricane intensity,” Gilford said.
