Hurricane Laura Live Updates: Category 4 Storm Slams Gulf Coast

“Know that it’s just you and God,” Mayor Thurman Bartie of Port Arthur, Texas, warned residents who were staying behind.

In Vermillion Parish, southwest of Lafayette on the Louisiana coast, the

sheriff’s office had a grim request for residents who did not leave: “If you choose to stay and we can’t get to you, write your name, address, social security number and next of kin and put it a ziplock bag in your pocket. Praying that it does not come to this!”

The storm was preceded by tough decisions about fleeing and an urgent push to get people out of harm’s way.

More than 500,000 residents in Louisiana and Texas were urged to flee their homes in recent days as Hurricane Laura roared toward the Gulf Coast. Laura intensified into a Category 4 hurricane on Wednesday afternoon as it churned through the warm waters of the Gulf of Mexico.

As the first bands of the expansive hurricane approached Lake Charles, his hometown, John O’Donnell hit a nearly empty Interstate 10, heading east for Lafayette or Baton Rouge.

He felt uneasy.

“This just doesn’t feel right,” Mr. O’Donnell, 33, said. “It doesn’t feel right leaving my city like this.”

A frequent city volunteer, Mr. O’Donnell said he had spent the last two or three days urging his fellow Lake Charles residents to evacuate. Privately, he sent his dog off with his ex-wife. Publicly, he posted on social media and drove 25 or 30 people to sites where buses carted them to safer havens outside the city.