The deadly typhoon that swept through the Philippines was one of the strongest ever recorded. But storms nearly this powerful are actually common in the eastern Pacific. Typhoon Haiyan’s devastation can be chalked up to a series of bad coincidences.

Typhoons — known in our part of the world as hurricanes — gain their strength by drawing heat out of the ocean. Tropical oceans are especially warm, which is why the biggest storms, Category 4 and Category 5, emerge there. These storms also intensify when there’s cool air over that hot ocean.

“The Pacific at this time of year is very ripe and juicy for big typhoons,” says Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology. “Once or twice a year we get a Category 5 typhoon out there.”