SAN JUAN, Puerto Rico — Tropical Storm Bertha swirled over the eastern Dominican Republic early Sunday morning after whipping Puerto Rico with heavy rains and strong winds that knocked out power in parts of the region.

The storm’s maximum sustained winds dropped slightly to 45 mph, but slow strengthening was expected by Monday. Bertha was centered about 30 miles east-northeast of Santo Domingo, Dominican Republic and was moving northwest at 21 mph Sunday morning.

The director of the Dominican Republic’s Emergency Operations Center, Juan Manuel Mendez, said that rain was falling on parts of the country but there were no reports of damage so far.

Officials were asking hotels and resorts in Punta Cana to cancel any planned water sports or activities and have prohibited tourist and fishing boats from taking to the water on the country’s east coast.

“Our obligation is to make sure that no person, national or foreign, experience problems” because of the storm, said Mendez.

Earlier Saturday, the storm passed just southwest of Puerto Rico, dropping between 3 to 5 inches (8-13 centimeters) of rain, with isolated amounts of up to 8 inches (20 centimeters).

Gov. Alejandro Garcia Padilla warned of flooding, landslides and swollen rivers, which he urged people not to try and cross.

“It’s something that sounds obvious but it happens so often,” he said. “It’s not the time to take risks.”

Authorities reported several downed trees in Puerto Rico’s eastern region and two downed electrical posts. Nearly 39,000 households were without power and more than 3,000 without water. The lights also had gone out at the island’s emergency management agency during a press conference Saturday morning.

Officials said most of the power outages occurred in the island’s central mountainous region following more than 1,200 lightning strikes that occurred in the area during afternoon hours alone.

The heaviest rains fell in the island’s southern and eastern regions, with authorities warning people to stay indoors.

Jose Colon Rivera, 50, who lives in a rural area near the southern town of Cayey, said in a phone interview that he could hear the wind whistling loudly through his zinc roof.

“If anything happens, I can always run,” said Colon, who was watching wrestling on TV as he waited for the storm to pass.

Some 220 people arrived at several government shelters in Puerto Rico’s southeast region, the majority of them international athletes participating in a youth baseball tournament.

Ingrid Vila, gubernatorial chief of staff, said Puerto Rico’s main international airport remained open but that several flights had been cancelled.

Authorities closed El Yunque rainforest, a popular tourist attraction in northeast Puerto Rico, and ferry rides to the neighboring islands of Culebra and Vieques were cancelled.

Downed trees limbs also were reported across St. Croix in the U.S. Virgin Islands, where a coastal buoy south of St. Thomas recorded wind gusts of 72 mph (115 kph).

Tropical storm warnings were in effect for the eastern Dominican Republic, southeastern Bahamas and the Turks and Caicos islands. A tropical storm watch was in effect for central Bahamas.

On Friday, Bertha passed just north of the French Caribbean island of Martinique, where it left 150,000 homes without power, government spokeswoman Audrey Hamann said in a phone interview. The storm also left hundreds of people without power along Dominica’s eastern region.

Antigua-based regional airline LIAT canceled several flights in Dominica, St. Lucia, Puerto Rico and the Dominican Republic. Seaborne Airlines also canceled flights in Puerto Rico and the Dominican Republic, while the U.S. Coast Guard closed ports in southern Puerto Rico.

The storm brought some rain to a drought-hit area of southern Puerto Rico, but it was not yet known whether it rained enough to cancel strict water rationing measures that are scheduled to start on Wednesday, authorities said.