“If it slips south, you’re stranded there!” Ms. Stovall, a theater director, told her.

And in South Florida, many Jewish families were trying to determine if they were allowed to work on boarding up their house or prepare to leave it over the Sabbath, which began at 7:25 Friday night. In Hollywood, Fla., Rabbi Gideon Goldenholz of Temple Sinai of Hollywood said they could.

“A hurricane is life-threatening,” he said, “so you have to do everything you can.”

Gov. Ron DeSantis of Florida said shoulders on Interstate 95 had been cleared for traffic and would be open when local evacuation orders were issued. The state, he said, would largely advise rather than direct local officials on whether to tell residents to flee.

“You will see evacuations. I’m confident of that,” he said, adding, “But we’re not going to be telling every county, ‘Tell everybody to leave,’ because that may create some problems as well.”

[Hurricane Dorian in pictures: See the preparations here.]

That dilemma has a long history. In Texas, nearly 100 people died in vehicles while trying to evacuate from Hurricane Rita in 2005. But tens of thousands of people who did not evacuate during Hurricane Harvey required rescue. Officials were criticized for their decision to evacuate or not to evacuate in both storms.

For Floridians watching as Dorian gathers strength off shore, it does not help that this particular storm has such a large “cone of uncertainty,” as the meteorologists say.

“The forecasts are so iffy,” lamented Terry Gellin, 69, a retired high school English and social studies teacher. “They say the storm has slowed down. What does that mean? There are just a lot of unknowns.”