There’s a new world order for Atlantic storms. Hurricane Erin was a preview

When Hurricane Erin explosively intensified in the Atlantic Ocean last week, the alarming part wasn’t solely how dangerous it had become as a Category 5 monster: It was also just how typical such an ultra-rapid rate of intensification – winds accelerating by 85 mph in 24 hours – has become.

Tropical cyclones have a greater propensity to rapidly intensify as the planet warms, studies have shown, which could imperil coastal populations that might have prepared for a tropical storm but suddenly face a menacing major hurricane.

It’s every emergency manager’s nightmare scenario.

Rapid intensification is defined as an increase in a storm’s maximum sustained winds by at least 35 mph in 24 hours, but in recent years, and certainly with Hurricane Erin, storms have far exceeded this threshold. Hurricane Milton, for example, had an intensification rate of 90 mph in 24 hours while traversing the Gulf’s ultra-warm waters last year, and Erin ranks in the upper echelon of historical Atlantic basin storms as well.

A shocking number of Atlantic hurricanes have rapidly intensified in recent years. Hurricanes Milton, Ian, Helene and Ida have all come in the past few hurricane seasons, at the same time as the Atlantic has broken records for hot ocean temperatures.

It’s not surprising that hurricanes are intensifying more rapidly, experts told CNN — but every hurricane shouldn’t be expected to explode into Category 5 status.

“There has been a notable increase in the proportion of (hurricanes) that have been going through rapid intensification and extreme rapid intensification” in the North Atlantic basin and globally, said Gabe Vecchi, a climate researcher at Princeton University.

“Erin was extreme, even in a warmer world,” he said, but the odds of its extremely rapid intensification rate “were made larger by historical warming of the tropics.”

Like Vecchi, Daniel Gilford, a climate scientist at the nonprofit research and communications group Climate Central, said the key link between the increased proportion of rapidly intensifying hurricanes and recent years lies in the warming oceans.

“There does seem to be consistent evidence suggesting that rapid intensification events are becoming more frequent with climate change, that as we continue to warm the planet, those sea surface temperatures are allowing rapid intensification to take place more frequently,” he said.

Climate Central published a rapid analysis looking at this connection soon after Hurricane Erin reached Category 5 status. It found that warming oceans due to climate pollution very likely made the difference in the storm reaching Category 5 intensity instead of becoming only a Category 4 storm with less destructive potential had it hit land.

But there are reasons to believe that rapidly intensifying hurricanes won’t continue to get worse — or even become the norm. And human-caused global warming might not be responsible for all the current trends. For example, the maximum potential intensity of a hurricane is governed not just by the temperature of the oceans but also by atmospheric factors, including the difference between the temperature of the lower and upper atmosphere, Kim Wood, an atmospheric scientist at the University of Arizona, explained.

“I always like to include the caveat that warming waters (rising sea surface temperatures) aren’t directly correlated with higher intensification rates,” Wood said in an email. Because the upper atmosphere has been warming too, this has increased atmospheric stability, which is the equivalent of tapping the brakes, at least slightly, on intensification rates and the maximum intensity a storm can reach if conditions are ideal.

Wood performed an analysis to determine how much more common rapid intensification rates are becoming and found higher-end intensifiers like Erin are seeing some of the largest jumps in frequency in the Atlantic, rather than storms that strengthen right at the definition of rapid intensification (35 mph in 24 hours).

Also, not all of the warming in the North Atlantic Ocean during the past several decades is directly attributable to global warming; it’s partially — and somewhat paradoxically — tied to the reduction in pollutants known as sulfate aerosols owing to clean air laws in North America and Europe in particular.

At the end of the day, however, the warmer the world gets, the more likely it is that fledgling tropical cyclones will take advantage of hotter oceans and other ingredients to skyrocket in their intensity, Gilford said.

“We’re living in a world where … there will be more Erins in the future, and these types of events like Erin will happen more frequently,” he said.

The forecasting challenge

Forecasters have improved their ability to predict rapid intensification in recent years, but track forecasts are still far more reliable than intensity projections.

Researchers at the National Oceanic and Atmospheric Administration (NOAA) and affiliated organizations have been tackling the challenge of anticipating when a storm may undergo rapid intensification, given the need for coastal regions to make evacuation decisions well in advance of landfall.

But, as was the case with Hurricane Erin, forecasts still can lag a storm’s rapid shifts.

“Rapid intensification of hurricanes is hard to predict and makes a storm have more damage potential very abruptly,” Vecchi said. This makes rapidly intensifying storms “unusually dangerous.”

He said making further investments in improving forecast accuracy while also reducing greenhouse gas emissions are both necessary to lessen the risks these storms pose. Proposed NOAA budget cuts could jeopardize some of the recent forecast gains, as well as delay or scuttle future improvements.

“Global warming has made rapid intensification much more likely, and we expect future warming to continue this trend,” Vecchi said.

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