Some of the largest cities in Southeast Asia could be hit by bigger, badder tropical cyclones in the decades ahead. A recent study found that warmer seas and air could change where storms in the region form, how quickly they ramp up, and how long they hang around. The changes could be especially deadly for major cities along the coast.

Researchers used computer models to simulate more than 64,000 cyclones in the region during three eras: 1881 to 1900, 1981 to 2000, and 2081 to 2100. For the future decades, they looked at what conditions would be like under both moderate and extreme warming for the rest of this century. They compared the results for past decades to real storm systems.

The models showed that tropical cyclones—both typhoons and smaller systems—are likely to be born farther north in the western Pacific Ocean, the South China Sea, and the Bay of Bengal, near India. That puts the storms closer to land. The systems are likely to strengthen much more quickly. And they’re likely to last longer after they move ashore. That means higher storm surges, heavier rains, and stronger winds—a deadly combination.

The study said the cities likely to be hardest hit are Bangkok, Thailand; Haiphong, in Vietnam; and Yangon, in Myanmar. Today, their combined population is about 17 million. But they’re expected to grow quite a bit by the end of the century—putting more people at risk from powerful tropical cyclones.