FORT LAUDERDALE, Fla. — It was a bit like a meteorological sucker punch. While most people had spent the previous week worrying about storms such as Emily, Gert, Herold and Franklin, Idalia took form off the Yucatan Peninsula and suddenly lashed out.
In a period of just over 24 hours, it went from being a mild-mannered tropical storm with winds of 70 mph to an enraged Category 4 hurricane with wind speeds of 130 mph.
The storm took just 12 hours to ramp from Category 1 to Category 3. And once the system became a hurricane, it only took a day for it to race across the Gulf of Mexico and pummel the Big Bend region of Florida’s west coast.
The National Hurricane Center dubs any storm that gains 35 mph or more of maximum sustained wind speed in a 24-hour period as “rapid intensifying.” Idalia gained 50.
This kind of rapid ramping can catch people off guard, and it may be a trend, according to experts. “Recent findings do point to it happening more often, particularly for extreme rapid intensification events well beyond the threshold definition,” said Alex DesRosiers, of the department of atmospheric science at Colorado State University.
Other rapidly intensifying Atlantic and Gulf storms in recent memory include:
—Ian (2022), which made landfall in Fort Myers as a Category 4.
—Ida (2021), which made landfall in Louisiana as a Category 4.
—Michael (2018), which made landfall in Mexico Beach as a Category 5 monster.
—Wilma (2005), made landfall in the Yucatan Peninsula as a Category 5 hurricane, then later the maximum sustained winds were estimated to be near Category 3 as its center went past southwest Florida near Cape Romano.
—Charley (2004), which ramped up from 110 mph to 150 mph in just a few hours before slamming Sarasota.
“Most storms that reach major hurricane status did so by rapidly intensifying at some point in the storm’s life,” said DesRosiers.
The sucker-punch speed comes from two main factors, said DesRosiers: sea surface temperature and lack of wind shear. Warm water acts as fuel, and wind shear, which knocks storms off balance, acts as a deterrent.
Sea surface temperatures need to be around 80 degrees or higher to be sufficient for hurricanes to form and intensify, DesRosiers said. Idalia experienced water temperatures close to 90 degrees as it passed over the Gulf.
There was also very little shear as the storm moved north toward Florida, DesRosiers said.
But there were two other factors that made Idalia especially punchy.
Storm posture and shape
The storm loitered for two days in the Yucatan Channel, the strait connecting the Gulf of Mexico and Caribbean Sea, giving the storm time to “get its act together and build the right internal structure,” DesRosiers said.
That internal structure has been notoriously difficult to study — it’s in the middle of a deadly storm and tough to see via satellite — but new technology is starting to offer better data, and thus better predictions.
University of Miami and National Oceanographic and Atmospheric Administration researchers on Virginia Key are using Tail Doppler Radar to create a three-dimensional image of the storm, almost like a CAT scan.
“It can give you an idea of how upright a storm is,” said Andrew Todd Hazelton, one of the researchers with the University of Miami. “Upright storms tend to intensify more quickly and tilted storms tend to intensify more slowly,” he said. That loitering in the Yucatan Channel helped Idalia gain the right posture.
Small and fast
The other factor that helped Idalia rapidly intensify was its size — it was not a particularly wide storm.
“It’s kind of like a figure skater, if their arms are spread out wide, they spin slower, if they move them in they spin faster,” said Hazelton. “Smaller storms can spin up faster, and with Idalia, at least the inner core was fairly small, so that may be one of the reasons it did intensify so quickly.”
Meteorologist Craig Setzer agreed, noting Idalia’s relatively small width.
“We know that small hurricanes are brittle, in a way, in that when wind shear hits them they can weaken very quickly, but they’re so small they can strengthen very quickly. Michael was similar. From that aspect, it was kind of the same with Andrew,” Setzer said, referencing the 1992 storm that devastated southern Miami-Dade County.
He makes the analogy of a tiny top being easier to spin quickly than a big bike wheel.
Heat and speed
As of July, global sea surface temperatures hit record highs for the fourth consecutive month in a row, according to NOAA, and South Florida saw its longest streak of heat advisories.
Sea-surface temperatures have been so high in the Atlantic and Gulf of Mexico this summer that NOAA shifted its prediction for the 2023 hurricane season to be “above-normal” activity.
Earlier in August, meteorologists were commenting on how hot the Gulf of Mexico was compared to the norm for August over time.
This can have a profound effect on hurricane intensity.
“You can think of a hurricane as a heat engine where the ocean is the fuel … so giving it warmer water is basically like higher-octane fuel,” Hazelton said.
If all other factors are optimal, the warmer the water the higher the potential intensity, he said.
DesRosiers said the increase in extreme rapid intensification events is “likely due at least in part to the warming oceans providing more fuel to hurricanes.”
As for the relationship of climate change, hot oceans and hurricane intensification, DesRosiers said “there is a present trend, although the magnitude of that trend is still being carefully scrutinized by researchers.
“The link to climate change is via our oceans, which warm as our planet warms, providing more fuel to storms.”