ST. JOHN’S, Antigua >> Tropical Storm Irene lashed the Caribbean’s Leeward Islands today with heavy rains and winds that closed airports, flooded roads, downed trees and temporarily knocked out power to thousands.

The fast-moving storm, packing winds of about 50 mph and tracking westward at 20 mph, was expected to strengthen and pass near the U.S. island of Puerto Rico later today or early Monday.

The U.S. National Hurricane Center in Miami said Irene could become a hurricane within 24 hours as it approaches Hispaniola, the island shared by the Dominican Republic and Haiti. More than 600,000 people in Haiti still live without shelter after last year’s earthquake.

“It’s slowly strengthening. It will probably become a hurricane within a day or so,” said Cristina Forbes, an oceanographer at the center. Sustained winds must reach 74 mph for the storm to be classified as a hurricane.

Most forecasts have Irene hitting southern Florida by the end of the week.

By late Sunday morning, Irene was 235 miles east-southeast of the southern Puerto Rican city of Ponce. The center said hurricane conditions were expected later Sunday in Puerto Rico and its outlying islands of Vieques and Culebra.

In advance of the storm, Puerto Rican authorities urged islanders to secure their homes and pick up debris that high winds could turn into dangerous projectiles. Maritime officials advised people to stay away from the ocean because Irene could bring a dangerous storm surge to the coast.

“I strongly recommend that swimmers and recreational boaters avoid the ocean and that the general public stay away from shoreline rocks until the tropical storm passes and weather and surf conditions normalize,” said Capt. Drew Pearson, a U.S. Coast Guard commander.

Early today, the storm churned up rough surf along a group of small islands in the eastern Caribbean that includes Antigua & Barbuda, St. Kitts & Nevis, Guadeloupe, and St. Maarten.

Although the storm caused some flooding in low-lying areas and several countries and territories reported scattered power outages, there were no immediate reports of serious damage or injuries. The storm was expected to dump up to 7 inches of rain on the islands.

“We are hoping that it won’t be too bad for us because we just can’t take this storm,” said James Henry, a fisherman on the island of Dominica who braved a gusty squall early Sunday to pull his small boat ashore.

In Antigua, the airport authority closed the V.C. Bird International Airport until at least midday. The tiny country of St. Kitts also closed its airport, stranding travelers who had hoped to beat the storm.

A hurricane warning was issued for an area stretching from the Dominican Republic’s southern border with Haiti to Cabo Franes Viejo on the north coast. A hurricane watch was also issued for the U.S. Virgin Islands.

Tropical storm warnings have been issued for all of Haiti, Saba, St. Eustatius, St. Maarten, Antigua, Anguilla, Montserrat, the U.S. Virgin Islands, and the British Virgin Islands.

Forecasters said tropical storm force winds extended outward up to 150 miles, mainly to the north of Irene’s center.