Hurricane Otis surprised forecasters with its intensity. Why are storms growing stronger?

When Tropical Storm Otis formed off the coast of southern Mexico, meteorologists expected heavy rainfall and mild winds once it made landfall. They were astonished when it hit Acapulco as a raging Category 5 hurricane.

In less than 24 hours, the storm's wind speeds increased by 110 miles per hour, a highly unusual and rapid intensification. Otis strengthened faster than any other tropical storm in the eastern Pacific and slammed into the popular tourist destination at about 1 a.m. local time on Wednesday.

Winds reached 165 miles per hour, taking out telephone and internet access in Acapulco and the surrounding area. At least 27 people have been killed and tens of thousands of residents are without electricity.

Rapidly intensifying storms like Otis are becoming more common, according to climate scientists, who are studying the effects of warming global temperatures on storms. The influence of El Niño conditions also could play a role in storm development.

"You have multiple players that all add up to more energy supply for hurricanes," said Shuyi Chen, a professor of meteorology at the University of Washington. "Climate certainly adds to sea surface temperature on top of El Niño."

Hurricane Hilary strengthened exponentially before flooding Southern California and southern Nevada in August. Devastating storms like Hurricane Harvey in 2017, Hurricane Laura in 2020 and Hurricane Ida in 2021 also intensified rapidly before landfall.

What's going on? Here’s what to know about Hurricane Otis and worsening tropical cyclones.

How do hurricanes form?

Tropical cyclones are powerful, rotating storm systems that form over warm ocean waters. These weather systems spin around a center of low pressure and cause thunderstorms, wind and rain.

During hurricane season, typically summer and autumn months, ocean waters are the warmest and spur more frequent tropical cyclone formation. If a cyclone reaches maximum continuous winds of 74 miles per hour or higher, it is classified as a hurricane, typhoon or cyclone, depending on where the storm originates.

Storms are called hurricanes in the North Atlantic and Northeast Pacific, typhoons in the Northwest Pacific and tropical cyclones in the South Pacific.

There are four conditions needed for a hurricane to form and strengthen: warm ocean water, elevated moisture in the air, minimal wind variation and a preexisting disturbance, like a group of thunderstorms.

To predict a storm's path, intensity and possible impacts, meteorologists and storm specialists use weather observations from satellites, radar and aircraft reconnaissance and analyze computer models.

Officials issue warnings and predictions accordingly, providing updates frequently before and after landfall. But storms like Otis show models are not always accurate.

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Why was Hurricane Otis so unusual?

Forecasters initially predicted Hurricane Otis would make landfall as a Category 1 storm, a mild storm with sustained winds of 74 to 95 miles per hour that usually cause minimal damage.

Instead, Otis underwent a phenomenon called rapid intensification. When rapid intensification occurs, the storm's maximum sustained winds rise by at least 35 miles per hour within 24 hours.

Otis’ wind speeds increased by 115 miles per hour within 24 hours, and 80 miles per hour within 12 hours of that window.

Chen believes the storm’s size played a role in its rapid intensification.

“Hurricanes need the center pressure to drop rapidly,” Chen said. “The smaller the eye, the easier it is for storm pressure to drop, so when you have a tight core storm they intensify faster than really large storms.”

While Otis expects meteorologists will address why computer models failed to predict the storm’s severity, she believes the storm’s small size and speed at which it developed caused this failure.

“The smaller the storm, the harder it is for hurricane models to capture,” she said.

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Does climate change play a role in intensifying storms?

Climate models predict storms will be less frequent, but hurricanes that do form will likely be more intense because of climate change. Hurricane Otis is part of a trend in tropical cyclone activity, with intensification occurring more quickly and frequently, according to a 2022 study.

Climate experts believe increased moisture in the air and warmer ocean temperatures are the catalysts.

As global warming advances, more water evaporates from the land and ocean, which adds more moisture to the air.

In a cyclone, rotating winds attract moist air to the center, which feeds the thunderstorms surrounding it. As air warms from climate change, hurricanes hold more water vapor, which contributes to rapid intensification of rainfall and winds during storms.

As Otis developed, it passed through 88-degree surface waters, which supercharged the storm.

“The research is really clear now that warmer ocean temperatures lead to increased hurricane activity with strength and intensification,” said Michael Crimmins, a climatologist from the University of Arizona. “Numerous papers have come out that have talked about warmer surface temperatures and warmer waters overall that are going to lead to stronger hurricanes and these situations where you can have rapid intensification.”

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How does El Niño contribute to hurricanes?

The National Oceanic and Atmospheric Administration announced an El Niño Advisory in June, signaling El Niño weather conditions that will strengthen through 2023 and into 2024. El Niño is a climate pattern in the Pacific Ocean that impacts weather globally.

Trade winds move warm water west, and cold water rises to replace warm water during normal conditions, a phenomenon called upwelling.

In an El Niño event, trade winds weaken and warm water is pushed east. This creates higher-than-average sea surface temperatures in the Pacific Ocean near the equator.

Hurricanes typically occur more frequently in the central and eastern Pacific and less often in the Atlantic during El Niño conditions.

According to Crimmins, this El Niño event is impacting the area off the southern coast of Mexico where Otis developed. He said the weaker winds bring in warm water, which likely helped the storm advance.

“The oceans are getting warmer, plus you have unusually warm water there because of the El Niño situation, so those factors combining really helped set up this situation,” Crimmins said.

Hayleigh Evans covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to hayleigh.evans@arizonarepublic.com.

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This article originally appeared on Arizona Republic: Why hurricanes are growing stronger in shorter time spans