MEXICO CITY — It was about midnight, as Hurricane Maria was battering the Caribbean nation of Dominica, that Prime Minister Roosevelt Skerrit took to Facebook. Roofs everywhere, he wrote, were being torn off by the powerful storm’s winds. He himself had to be rescued from his official residence.

“We will need help, my friend, we will need help of all kinds,” he said, describing the damage as “mind-boggling.”

And then silence. From Mr. Skerrit — and, it appears, from the rest of the island.

As the storm, described by the National Hurricane Center as “potentially catastrophic,” moved toward the Virgin Islands and Puerto Rico on Tuesday, little could be learned about the conditions on Dominica. By early Tuesday morning, phone and internet signals on Dominica appeared to be down, leaving the island virtually incommunicado.