Experts who reviewed the video said the interpreter spelled the wrong words and gesticulated gibberish.

Mr. Rosenblum tried to decipher the beginning, starting when officials announced the evacuation, but he could only make out a jumble of disconnected phrases. “On that news” was followed by “need evacuate” and later, “pray wait water.”

The interpreter also appeared at a news conference later that day — wearing the same yellow shirt.

The county posted highlights from its news conferences on Facebook, including a searchable map of evacuation zones and information about shelters. But being unable to understand the live news conferences put the deaf population on edge.

“It was really a stressful day for sure,” Julie Beacham-Hooie, 47, who is deaf, said through an interpreter in a phone interview.

“I was watching the interpreter and seeing him spelling and spelling and spelling, and not fully signing,” said Ms. Beacham-Hooie, who lives in Bradenton, Fla., about 45 miles south of Tampa, Fla. “It was very hard to follow.”

She turned to the internet for more information and relied on her sister in Nevada. “I asked other people if the hurricane was actually headed straight for us,” she said. “I had no idea.”