Why Hurricane Helene grew so rapidly into a monster storm

Hurricane Helene crashed into Florida’s west coast late Thursday night, dropping heavy rain and a powerful storm surge. Videos of flooded homes and roadways, downed trees and infrastructure and precarious rescue attempts inundated social media platforms, underscoring the storm’s severity.

What added to the risks was how fast it all happened. Helene is the latest example of a dangerous meteorological phenomenon called rapid intensification , something that is becoming increasingly common due to climate change and atmospheric and oceanic shifts.

The storm slammed into Florida’s Big Bend region with 140-mile-per-hour winds and was the first Category 4 hurricane to hit the area since records began in 1851. It had been downgraded to a tropical storm by Friday morning, but will continue north through Georgia and the Carolinas.

Meteorologists began tracking tropical activity in the Caribbean on Sept. 23 and watched Helene form. They sounded the alarm when it grew from a Category 2 to a Category 3 storm in just a few hours, a clear example of rapid intensification.

That phenomenon occurs when a storm increases its wind speed by at least 35 miles per hour within 24 hours.

“It is becoming more common, particularly near coastlines,” said Randy Cerveny, professor of geographical sciences at Arizona State University. “It’s not just Florida; it’s not just the United States. We’re seeing rapid intensification occurring around the world, and we think that is in part due to climate change, because of the activities of humans.”

Hurricane Hilary strengthened significantly before flooding Southern California and Nevada last summer. It joined the ranks of superstorms like Hurricane Harvey in 2017, Hurricane Laura in 2020 and Hurricane Ida in 2021 that intensified rapidly before landfall.

Here’s what to know about Hurricane Helene and rapid intensification:

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What causes rapid intensification?

Tropical storms and hurricanes are intensifying more quickly and frequently, which scientists attribute to climate change and atmospheric trends.

As Hurricane Helene approached Florida’s coast, it traveled through 85-degree waters.

“That is incredibly hot waters, and hot water is what powers a hurricane,” Cerveny said. “It becomes more intense as it’s able to draw on the energy of that hot water. The water temperature along the coastlines is increasing, which provides fuel for these hurricanes.”

Once a storm hits land or cold water, it will begin to die out. But as these storms approach warm coastlines, they acquire the optimal conditions for rapid intensification.

As humans introduce more planet-warming greenhouse gases into the atmosphere, the oceans absorb more heat, increasing sea surface temperatures.

El Niño-Southern Oscillation (ENSO), a recurring climate pattern that impacts temperature and pressure in the Pacific Ocean, also plays a role in rapid intensification.

Going into the 2024 hurricane season, meteorologists expected a stronger season with frequent storms in the Atlantic as the Pacific approached a La Niña period. La Niña is a cool phase of ENSO that triggers cooler temperatures in the Pacific.

This pattern can also reflect warmer temperatures in the Atlantic, supercharging hurricane activity. While forecasters predicted an active season, that has not been the case so far.

“This has been a very weird summer and fall in the northern hemisphere,” Cerveny said. “We were anticipating that this was going to be an incredibly active season, but we’ve had a huge amount of dust come off the Sahara Desert that tends to suppress hurricane activity.”

Cerveny said the forecasts were “overblown” due to the large quantities of dust in the atmosphere, but their luck has temporarily run out with Helene’s impact.

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How does rapid intensification affect forecasting?

While forecasters accurately predicted Helene’s development days in advance, that’s not always the case with storms that undergo rapid intensification.

“Rapid intensification changes the character of the storm,” Cerveny said. “It makes it so intense, that it starts to influence the climate and weather around it and can make it move in ways that we wouldn’t have predicted.”

Last year’s Hurricane Otis slammed into Mexico as a Category 5 hurricane, with wind speeds increasing by 115 miles per hour within just 24 hours. Computer models failed to predict the storm’s severity, catching Acapulco mostly off-guard.

But modeling has steadily improved. Meteorologists predicted Helene’s severity, although rapid intensification pushed the storm 150 miles east of where they initially predicted.

Despite its distance from the Atlantic, the Southwest also played a role in shaping the hurricane’s path.

“What has played a factor, is our heat helped move Helene on the path that it did,” Cerveny said. “The big high-pressure system that has been sitting over the Southwest forced Helene to go north. The high-pressure system acted as a big block that forced the hurricane to travel straight northward.”

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How does rapid intensification make storms more dangerous?

Storms that rapidly intensify can be more dangerous and cause significant damage to everything in their path. While Hurricane Helene likely won’t be the strongest storm to ever hit Florida, its damage will extend through the state and beyond.

Cerveny believes long-lasting rainfall, particularly in the southern Appalachians, can cause major flood problems. Even as the rain and water recede, residents are exposed to mudslides and days without power.

While all storms require caution, storms that rapidly intensify should be taken especially seriously by those in their path.

“We have to pay more attention to the coverage with rapid intensification because things can change within a matter of hours,” Cerveny said.

“If you’re basing whether you’re going to stay or go based on something that was said 12 hours ago, if we’re having rapid intensification, that’s going to be wrong now,” he continued. “Things change so fast, that it can completely change what you should do for a particular storm.”

Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic and azcentral.com . Email her with story tips at hayleigh.evans@arizonarepublic.com .

This article originally appeared on Arizona Republic: Why Hurricane Helene grew so rapidly into a monster storm