How hurricane became a hulk
Hurricane Otis turned from mild to monster in record time, and scientists are struggling to figure out how — and why they didn’t see it coming.
Usually reliable computer models and the forecasters who use them didn’t predict Otis’ explosive intensification, creating a nightmare scenario of an unexpectedly strong storm striking at night. Acapulco was told to expect a tropical storm just below hurricane strength on Wednesday, but 24 hours later, Otis blasted onto the Mexican coast with 266km/h winds, the strongest landfall of any East Pacific hurricane.
In just 12 hours, Otis’ strength more than doubled from 113km/h winds to 257km/h, also a record, as it neared the coast. And it got even stronger before it struck. Storms typically gain or lose a few km per hour in 12 hours, though some outliers gain 48 to 80km/h in a day.
What happened with Otis was just plain nuts, said University of Miami hurricane researcher Brian McNoldy.
But it coincides with a documented trend of hurricanes rapidly intensifying more often in recent decades because of warmer water connected to climate change, scientists said.
Five different hurricane experts told AP they weren’t quite sure what set Otis off and why it wasn’t predicted, especially since meteorologists have been dramatically improving their intensity forecasts in recent years.
“The models completely blew it,” said MIT atmospheric sciences professor Kerry Emanuel, a hurricane expert.
Experts point to lack of data on the storm and its surroundings and just not completely understanding what makes a storm act like it’s on steroids.
And it really matters because in Otis’ case, the storm was coming ashore when it muscled up.
“It’s one thing to have a Category five hurricane make landfall somewhere when you’re expecting it,” McNoldy said. “But to have it happen when you’re not expecting anything to happen is truly a nightmare.”
For example, McNoldy, who lives in Miami, said a tropical storm forecast would prompt him to “do things like move some lightweight furniture in and take down wind chimes and things like that. That’s about it. You’re not preparing for a Category five hurricane.”
National Hurricane Centre Director Michael Brennan said “that’s a very bad scenario, populated area, rapid intensification very close to landfall, a change in the expectations about the impacts that’s happening on a time scale that doesn’t give people a lot of time to respond.” Brennan said Otis’ unforeseen buildup was because “it found a much more favourable environment than we were anticipating”. He said one part was warm water, another was that the winds — moving in the right direction and at the right altitude — allowed a somewhat raggedy storm to rapidly develop structure and strengthen.
Globally, the world’s oceans have been setting monthly surface heat records since April. The surface waters off the Mexican coast were warm. Below that, the water was much hotter than usual.
Otis and two other historically explosive cases of rapid intensification — Patricia in 2015 and Wilma in 2005 — all happened in the same mid- to lateOctober time frame, when deeper water and ocean heat content is at its highest, McNoldy said.