Hurricane Otis’ growth to Category 5 storm surprised forecasters. Why?

The storm, which has killed at least 27 people, was originally forecast to hit the southern-Pacific region of Mexico as weak hurricane.

Hurricane Otis slammed into the southern-Pacific part of Mexico early Wednesday morning, downing power lines in communities including the popular tourist city of Acapulco. The hurricane damaged buildings and flooded roads and it’s left many wondering how forecasters didn’t see the Category Five storm coming.

The storm, which has killed at least 27 people, was originally forecast earlier this week as one that would hit the region as a weak hurricane.

It took many by surprise on Tuesday evening when it rapidly strengthened from a tropical storm to a powerful hurricane as it tore along the southern coast.

Daniel Brown, a senior hurricane specialist at the National Hurricane Center in Miami, Fla., told Global News that the modelling did not give meteorologists indication there would be such a significant strengthening. He said while there was initially a “vertical wind shear” over the storm, it appeared to have “relaxed” by Monday night.

“Rapid strengthening is one of the most difficult aspects to forecast of hurricanes,” he said. “We have gotten better in very recent years of forecasting rapid strengthening. But this really was an extreme case.”

Brown said “rapid strengthening” is defined as about a 35 mile-per-hour, or about 56 kilometre-per-hour, increase in winds over a 24-hour period, adding Otis “essentially doubled, almost tripled that rate of intensification” before it hit the coast of Mexico.

According to Global News chief meteorologist Anthony Farnell, the storm — which reached winds of approximately 265 km/h — saw a ramp-up of about 125 km/h in just 12 hours.

What made the storm worse, especially for those in Acapulco, was that it hit at night, making it more difficult for people to get advance warning whereby they would have time to get to higher ground, according to Farnell.