On Monday morning, Hurricane Ian had wind speeds of 75 miles per hour. Just 48 hours later, those speeds had more than doubled. On Wednesday, as the storm made landfall in southwest Florida, Ian’s winds hit 155 mph — just shy of a Category 5 storm, the worst category for a hurricane.
Such rapid growth is known to meteorologists as “rapid intensification.” It is defined as storms whose wind speed increases by about 35 mph or more in less than 24 hours. “Ian certainly met those criteria,” said Paul Miller, a professor of oceanography and coastal sciences at Louisiana State University.
While wind speed isn’t the only force that makes storms dangerous, hurricanes that are increasing rapidly are especially worrisome. They can easily overwhelm coastal communities, leaving them little time to prepare, Miller said.
So how did Ian get so big, so fast?
It’s an important question, because storms like this are highly destructive and are likely to become more frequent in the coming years.
What made Hurricane Ian stronger so quickly?
There are three main ingredients that, when mixed together, can result in a rapidly intensifying hurricane: moist air, low wind shear (winds come from different directions or at different speeds), and warm ocean water.
“All of these three things create a favorable ecosystem for a hurricane to establish and intensify circulation,” Miller said.
Ian had them all. As it developed several days ago, the storm system faced some disruptive winds, but there was little shear as it grew in recent days, Miller said. And Ian has largely avoided an area of dry air in the Gulf of Mexico. (If Ian had hit Florida further north, it might have deteriorated faster, he said.)
Then there is the warm ocean water. The Gulf of Mexico is unusually warm this summer, according to the National Weather Service. And climate change is warming the Caribbean ocean slightly more than 1 degree C (1.8 degrees Fahrenheit) per century.
“Even small changes — half a degree C or a degree — can really make a big difference,” said Brian McNoldy, a hurricane researcher at the University of Miami.
Another reason the ocean is so warm is that it has been a relatively calm hurricane season thus far. As hurricanes chug through the Caribbean, they suck heat from the water and spin it up, making it colder and less favorable for rapid intensification, Miller said.
“We’ve been able to let the Gulf sit and bake throughout hurricane season,” Miller said. “We haven’t had another storm this season to go through and cool the Gulf through that mechanism. There’s this pristine Gulf of Mexico from a sea surface temperature standpoint, and Hurricane Ian has been able to take advantage of that.”
Rapidly intensifying storms are difficult to predict and therefore difficult to prepare
Forecasters have made great strides in figuring out where hurricanes will go. Storm track predictions that could only be made 24 hours in advance 20 years ago can now be issued 72 hours ahead.
But it was harder to anticipate how strong storms will get. (Example: As of Sunday night, Ian was predicted to) peak at 130 mph).
That’s because there are so many factors that affect the intensity of a storm, and they can change quickly over time and space. Remember that rapid intensification occurs when hurricanes pass over areas of calm, warm water. But it’s not just how warm the ocean is on the surface; how deep the heat goes also matters. Measuring the depth of warm water and predicting sea surface conditions can be tricky. Often it requires hurricane fighter aircraft drop temperature sensors in the ocean before the storm.
With a limited view of a hurricane’s potential intensity, it is more difficult to issue warnings and evacuation orders.
That happened last summer as Hurricane Ida galloped toward Louisiana. The storm jumped in strength from Category 2 to Category 4 in less than a day, with winds exceeding 150 mph. The sudden acceleration left little time to coordinate logistics to get people out of the storm’s path.
“We didn’t have the time with Ida to safely enforce a mandatory evacuation where we would put more than a million people on the road,” said Collin Arnold, director of New Orleans Homeland Security and Emergency Management. told WVUE Fox 8 last year.
Now it’s happening again with Hurricane Ian. In some parts of Florida, “it is no longer possible to evacuate safely,” Florida Governor Ron DeSantis said on Wednesday. “It’s time to crouch down and prepare for this storm.”
So predicting the intensity of a storm is not just an academic exercise, but a life-saving tool. Better predictions are part of why fewer people die in extreme weather events, even as those events become more destructive.
But people also have to take predictions into account. And a hurricane’s impact doesn’t stop when the storm blows itself out. Floods can last for days, and as Puerto Rico showed after Hurricane Fiona swept through us last week, power cuts can continue, jeopardizing access to food, lighting and clean drinking water. So Floridians won’t be out of danger when the wind dies down and the water recedes; at least they’re vulnerable until the lights come back on.
Is Climate Change Making Storms Grow Faster?
If climate change warms the ocean and warm oceans feed storms like Ian, does that mean climate change is making storms grow faster? Possibly.
According to a recent analysis from hurricane data by the Associated Press, there have been about 25 percent faster intensifying storms in the Atlantic and Eastern Pacific over the past 10 years compared to 40 years ago. Some previous scientific studies have also found: shown that hurricanes are increasing faster in parts of the Atlantic in recent years.
“As the oceans warm up a little, you gradually make” [rapid intensification] more likely,” McNoldy said.
Global warming could also help storms quickly intensify in another way: Climate change tends to warm the land faster than the sea, creating a temperature gradient along the coasts, said Karthik Balaguru, a climate scientist with the Pacific Northwest. National Lab. That gradient tends to favor the rapid intensification of hurricanes along the Atlantic coast, he said.
But it’s worth keeping in mind that stepping up is a complicated process, Miller said. And other factors influencing these events (wind shear and humidity) are not clearly linked to climate change, he said.
“Nobody gets it 100 percent,” McNoldy said of stepping up.