“POTENTIALLY catastrophic”—that was how America’s National Hurricane Centre described Hurricane Patricia as it barreled menacingly towards Mexico’s Pacific coast on the afternoon of October 23rd. Extraordinary photographs taken from space showed an image of what looked like a perfect storm. “It’s massive. Be careful!” tweeted Scott Kelly from the International Space Station. With sustained winds as high as 320kph (200mph), and gusts well above that, it was declared to be the most powerful hurricane ever recorded in the western hemisphere. Yet 48 hours after it hit Mexico, no reports had come in of major damage, and Hurricane Patricia was being blamed directly for just two deaths, caused by a falling tree.

As the storm built up quickly in the Pacific there had been good grounds for concern. Many Mexicans would have remembered the sufferings inflicted by earlier storms. In October 1959 the only previous east Pacific hurricane to make landfall at Category 5 (ie. with a wind speed above 252kph) was responsible for between 1,000 and 2,000 deaths in Mexico. In October 2002 Hurricane Kenna, a Category-4 wind that struck Mexico’s Pacific coastline around 100km north of Puerto Vallarta, caused a five-metre storm surge. In September 2013 the country was hit by Hurricanes Manuel and Ingrid in the space of 24 hours, one on each coast, which together caused more than 150 deaths. And by way of deadly comparison, they would have been aware that in November 2013 a storm of similar size to Patricia, Typhoon Haiyan, tore through the Philippines and caused the loss of over 7,000 lives. Why then did this most recent hurricane fail to deliver the cataclysm feared?

Several factors appear to have played a role. Firstly, Patricia made landfall at a relatively quiet stretch of coastline between the towns of Puerto Vallarta and Manzanillo, rather than directly—and more dangerously—over either of them. It then moved quickly enough that its rainfall was not concentrated in any one place, thus reducing the chances of flooding. Its really strong winds were to be found within 50km of its “eye”, making it a comparatively tight storm. And those same winds were rapidly weakened when they passed over the Sierra Madre Occidental, mountains near Mexico’s western coast. Topping this all off, the accompanying storm surge, which was responsible for most of Typhoon Haiyan’s fatalities, caused no problems. It seems the shape of the local seabed prevented the build-up of shallow water necessary for a large surge.