NASSAU, Bahamas -

A tropical depression formed over the Turks and Caicos Islands on Saturday as it headed toward the Bahamas and dumped heavy rains on parts of Puerto Rico and the Dominican Republic, according to the U.S. Hurricane Center.

It is the fourth depression of the Atlantic hurricane season, and the system is expected to strengthen into a tropical storm on Sunday as it passes over or near the central Bahamas. The depression has sustained winds of 35 mph (56 kph) and was located about 75 miles (120 kilometers) northeast of Great Inagua island on Saturday afternoon.

A tropical storm warning has been issued for the Turks and Caicos and for the southeast and central Bahamas, with forecasters saying it could bring up to 8 inches (20 centimeters) of rain. The depression is moving northwest near 12 mph (19 kph).

The storm was upgraded to a tropical depression on Saturday afternoon, and it had previously downed several trees and power lines in Puerto Rico, leaving more than 17,000 people without power and nearly 5,600 without water. Police said in a statement that a small bridge collapsed Saturday in the central town of Barranquitas, isolating some 25 families in the area. No one was injured.