Otis intensification a ‘monumental miss’ by weather models

Weather modelling failed to predict the rapid intensification of Hurricane Otis, which became the biggest every hurricane to make landfall in northwestern Mexico and cut off the popular tourist resort of Acapulco.

While there have been few reports on economic or insured losses yet, the hurricane’s rapid

Growth signified a “remarkable and monumental ‘miss’ or ‘bust’ by all the weather models”, according to a report by Moody’s RMS.

In a report issued today, RMS said the failure to predict the onset and magnitude of Otis’ intensification will have had serious implications for preparations and evacuations in Acapulco and the surrounding areas on Mexico’s west coast.

“While hurricane warnings were issued 24 hours before landfall, this was when the forecasts called for a Category 1 landfall,” the report said. “Only within 12 hours of landfall did the forecast landfall intensity increase to a Category 4 major hurricane.”

It added: “The full extent of the wind, storm surge, and rainfall damage in Guerrero will emerge over the coming days. Nevertheless, Hurricane Otis provides a new data point for studying rapid intensification, and one that will need to be learned from for the future.”

The report said Otis appeared to be an ordinary tropical storm 24 hours before it hit Acapulco but rapidly intensified to a category 4 storm and made landfall as a category 5 storm with sustained winds of 165mph.

“This makes Otis the strongest hurricane on record to make landfall on Mexico‘s Pacific coastline, surpassing Hurricane Patricia which made landfall with winds of 150 miles per hour on October 23, 2015, the report said.

Only when a Hurricane Hunter aircraft was deployed to investigate Otis and provide real-time observations from the heart of the storm, did the true strength of the storm become clear, Moodys said.

“The aircraft penetrated its eyewall at around 19:00 UTC and 20:00 UTC on October 24 and found that the maximum sustained winds had increased to nearly 110 knots over a very small area near its centre, while the central pressure remarkably dropped around 10 hPa from the first to the second centre pass through.”

RMS added: “Its rate of intensification was three times the criteria for ‘rapid intensification’ – a rate only exceeded in the Eastern North Pacific basin by Hurricane Patricia in 2015, a storm that intensified by 105 knots in 24 hours.

“Patricia’s rapid intensification and peak intensity were situated over water, whereas Otis continued to intensify right up to the moment its centre crossed the coastline. The intensification rate of Otis is likely to be among the top ten all-time rates of intensification.”