Nana was downgraded to a tropical depression by the U.S. National Hurricane Center in Miami at 11 a.m. The system was 1,050 miles west of the Cape Verde Islands with sustained winds of 35 mph. It was moving west-northwest at 7 mph, the center said.

Meanwhile, a storm in the eastern Caribbean Sea strengthened further to become Tropical Depression 15 Monday, and was expected to strengthen further to tropical storm status later in the day, forecasters said.

The report said the storm was 340 miles southwest of San Juan, Puerto Rico, moving northwesterly at about 2 mph over very warm waters, which fuel strengthening.

The hurricane center said No. 15 was a large depression likely to bring heavy bands of rain to Puerto Rico and the Virgin Islands Monday.

Early in the day, the National Weather Service in San Juan issued a flash flood warning for Fajardo, Puerto Rico, where rain had already pushed the Rio Fajardo river past flood stage.