Rapid Intensification: How a storm can go from unnamed, to a major hurricane in 48 hours

CHARLOTTE — Time saves lives in severe weather emergencies, which is why the National Hurricane Center works to get out its storm forecasts well before tropical systems make landfall.

It’s especially crucial with a storm like Helene, which, as of Tuesday, looks nothing like NHC predicts it will when it makes landfall Thursday evening.

Tuesday morning, it hadn’t even formed and by Thursday, it’s expected to become a major hurricane, Category 3 or higher, due to a process called rapid intensification.

John Nielsen-Gammon, who studies the phenomenon as the Texas state climatologist, explains rapid intensification is exactly what it sounds like. Under the right conditions, tropical systems can see their wind speeds increase by 40 mph or more within a 24-hour period.

“That corresponds to basically an increase of at least one category, generally more,” he said.

It’s happened with a few recent storms in the Gulf of Mexico. Hurricane Ida in 2021 was a dramatic example, growing from a Category 1 to a Category 4 in 24 hours due to a combination of humid air, low wind shear and a very warm Gulf of Mexico.

Ahead of Helene, NHC and Nielsen-Gammon agree we’re seeing similar conditions.

“It’s pretty clear from the forecast as moving into an area environment that is increasingly favorable for development, and it’s already developing and slowly intensifying, even when conditions aren’t optimal,” he said.

The Gulf of Mexico has been trending warmer for decades and remains abnormally warm as Helene enters its waters.

While there’s not enough evidence to support that this warming trend is producing more storms, Nielsen-Gammon said it can make rapid intensification more likely with warmer waters fueling these storms.

“It basically increases the upper limit on how strong this storm could potentially become,” he said.

Nielsen-Gammon said meteorologists are still researching the ways climate change could be impacting hurricanes, but scientists have growing confidence that rising sea levels are worsening storm surges and warmer waters are fueling higher rainfall totals.

“Basically storms over warmer water can carry more water vapor with it and dump more water onto the land,” he said.

Meteorologists are taking these trends into account as they put together their forecasts, so although a storm may look small days before it makes landfall, Nielsen-Gammon said those in harm’s way should heed those warnings.

“People understandably put more trust in what the storm is like now than a forecast of what it’s going to be like in the future,” he said. “Don’t plan on what the storm is like now. Plan on what it’s going to be like at landfall, which is going to be quite a bit different.”

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