By John Marino

SAN JUAN, Puerto Rico, Sept 22 (Reuters) - A tropical disturbance dumped up to 20 inches (51 cm) of rain on Puerto Rico, killing four people and flooding scores of homes, businesses and roads, authorities said on Monday.

Up to 12 inches (30 cm) more rain were expected and flash flood warnings were posted across the island. Schools and many businesses were closed and officials urged people to stay inside.

"We are expecting it to continue raining throughout the island and anticipate up to 12 inches in the southeast," Gov. Anibal Acevedo Vila said at a press conference.

The weather system has the potential to develop into a tropical storm by Wednesday as it moves northwest away from Puerto Rico, said National Weather Service meteorologist Sean Rossi.

If the scattered mass of thunderstorms becomes well organized with winds of 39 miles per hour (63 km per hour), it would become Tropical Storm Kyle.

Computer forecast models took it north-northwest over the Dominican Republic and Haiti and then into the Atlantic. Haiti has already been hit hard by recent hurricanes and tropical storms. About 700 people died when the impoverished nation was hammered by floods triggered by torrential rains from Fay, Gustav, Hanna and Ike.

Some anticipated the latest tropical weather system would hit the Carolinas or the northeast U.S. coast, while other models kept it over the open seas. It was not expected to enter the Gulf of Mexico, where U.S. oil and gas facilities were still recovering from Hurricane Ike.

In Puerto Rico, the U.S. territory's southern coast was hardest hit by flooding. Several rivers, including the Rio Grande de Arecibo and Rio de La Plata, surged over their banks.

Scores of roadways were flooded and two major highways were partly closed because of mudslides.

A 52-year-old man drowned after his car was swept away by floodwaters on Sunday and a 44-year-old man drowned while trying to rescue another motorist whose car was stuck in a flooded road, police said.

A third man was driving with his wife and suffered a fatal heart attack when their vehicle was swept up in floodwaters. The fourth victim suffered a fatal heart attack while trying to remove water from his flooded home, police said.

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