Hurricane Katrina struck the Gulf Coast on Aug. 29, 2005, with wind gusts exceeding 130 miles per hour and a surge of water taller than a two-story building. The water left the coast in ruins and swelled through the broken levees of New Orleans as a wave that left 80 percent of the city flooded for days. Nearly 1,400 people died.

Two days earlier, Max Mayfield, then the director of the National Hurricane Center, had made a call to the city’s mayor. Mr. Mayfield said he recalled that after they had hung up he turned to a person next to him and expressed concern: “He doesn’t get it.”

Days before the storm hit the Gulf Coast, forecasters at the Hurricane Center knew where Katrina would go and how strong it was likely to be. They knew it would follow nearly the exact same path that Hurricane Camille — still one of the most intense hurricanes on record — had in 1969.

But Mr. Mayfield said he and others had trouble persuading people in the storm’s path to take it seriously. “If you don’t communicate that forecast to the right people effectively, it’s no good,” he said. “If people don’t respond, it is wasted effort.”

Michael Brennan, the current director of the Hurricane Center, said that since Katrina, meteorologists and other emergency officials had learned crucial lessons not just about how to forecast hurricanes but about communicating the dangers they pose.

Katrina wasn’t the first hurricane to hit the city, and won’t be the last. Here’s what’s different now.