Residents and visitors to the popular resort town of Acapulco went to sleep on October 25, expecting a rainy and windy night as Otis approached. Earlier in the day, Otis was a tropical storm. A soaker was coming, but there was no reason to expect what happened next.
Less than 12 hours later, in the wee hours of Wednesday, October 25, Otis swelled to a monster Category 5 hurricane. Acapulco’s inhabitants were jolted awake by shattering glass while climate scientists worldwide grappled with fractured assumptions.
Among the largest storms ever to make landfall in Mexico, Otis was also the second fastest-intensifying storm ever recorded.
Hurricane Otis is the latest and most extreme example of a trending new extreme weather reality: hurricane rapid intensification.
What is Rapid Intensification?
Rapid intensification occurs when a storm’s wind speed increases by at least 35 miles per hour within 24 hours.
Observed primarily in the Atlantic, Otis was out of place and time, landing on Mexico’s Pacific coast, cranking up 115 mph in about 12 hours, and outrunning our ability to build predictive models and warn communities.
Forecasting rapid storm intensification is challenging. With Otis, it became overwhelming, demonstrating the urgency of expanding data collection, expediting its analysis, and reconsidering our stochastic assumptions in a quickening climate.
What drives this newly-precedented storm (“unprecedented” seems inadequate these days) to gather such energy and strength in such a short time?
If you guessed heat, you’d be right. Earth is a planetary-sized heat engine. The land, oceans, and atmosphere are vast conveyors of heat—especially the ocean, covering 70% of the planet.
Oceans have absorbed up to 90% of the atmospheric heat driven by burning fossil fuels. New research published in Nature Communications shows an alarming ocean warming trend. Rising significantly since the 1990s, the study shows a doubling of average global ocean heat since 2010.
Ocean heat is among the many records broken in 2023. It helps explain how storms like Otis are pushing the boundaries of the new normal.
High-Octane Hurricane Fuel
Hurricanes draw heat energy from warm ocean surface waters of at least 26.5 degrees Celsius or about 80 degrees Fahrenheit. This warm water is “hurricane fuel,” meteorologist Richard Knabb told CBS News. “Think of the ocean as the gas tank for the hurricane that is the engine,” said Knabb.
“The more high-octane fuel you give it, the more it is able to accelerate in terms of its maximum speed, and the fuel they use is the warm waters of the ocean. The hurricane converts the energy in the ocean into low pressure that generates all the wind.”
A warming ocean provides the “high-octane fuel” driving Otis and other rapid intensification storms. As the storm churns the warm surface, cooler sub-surface water helps moderate storm intensification.
But when that heat penetrates down the water column, instead of a damping effect, it’s like turning up the heat on a kettle of water—the higher the heat, the faster the water boils. In the case of ocean-driven storms, the faster and more intense they become.