The storm formed Monday east of the Windward Islands, the National Hurricane Center said. It is forecast to strengthen into a hurricane by the end of the week.
A spokesman for the U.S. Coast Guard said the five people on the submersible theoretically had 70 to 96 hours of oxygen before the situation became dire.
A search-and-rescue mission is underway in the North Atlantic for the missing craft, the Coast Guard said. It is unclear how many people were on board.