MIAMI - Hurricane Sandy pounded the Bahamas early Friday as it careened toward the eastern United States after claiming 21 lives in the Caribbean, including 11 people killed in eastern Cuba.

US forecasters downgraded the storm to a category one hurricane late Thursday after it wreaked havoc in Jamaica, Cuba, the Bahamas and Haiti, downing power lines, damaging hundreds of homes and ruining crops.

But the forecasters warned that the massive hurricane could collide with a seasonal “nor’easter” weather system as it churns up the East Coast, becoming a potentially devastating “Frankenstorm.”

“The high degree of blocking from eastern North America across the entire Atlantic Basin is expected to allow this unusual merger to take place,” forecasters at the Miami-based US National Hurricane Center said Thursday.

The meteorologists said the combination of adverse weather conditions could affect the area through Halloween on October 31, “inviting perhaps a ghoulish nickname for the cyclone along the lines of ‘Frankenstorm’.”

In its 0900 GMT bulletin, the NHC said Sandy was packing sustained winds of 80 miles (130 kilometers) per hour as it moved north as a category one storm on the five-point Saffir-Simpson wind scale.

The hurricane was moving northwest at around 13 miles per hour. It was expected to weaken further in the next 48 hours but remain a hurricane.

The NHC’s latest forecast model has the hurricane moving parallel to the East Coast before swerving to the northwest and slamming into the heavily populated mid-Atlantic just north of Washington, DC early Tuesday.

The Bahamas were still bearing the brunt of the storm, with power and phone lines downed, tourists stranded and trees uprooted. Schools, government offices, airports and bridges were to remain closed Friday.

Sandy claimed 11 lives in eastern Cuba, including several who died in the rubble of buildings that collapsed in the fury of the massive storm.

The hurricane damaged hundreds of homes, flooding crops and downing trees, according to media reports.

“It was terrible. Roofs were flying off lots of houses. Doors too, and windows,” said Laquesis Bravo, 36, who lives outside the southeastern coastal city of Santiago de Cuba.

Nine people died in Santiago, including a four-month-old infant who was among four people who perished when a house caved in. Five more people in the province died during the storm for unspecified reasons, while two people in the nearby town of Guantanamo were killed by falling trees.

On Wednesday, Sandy unleashed its wrath on Jamaica, where one person died, and on Haiti, where nine people died and three others were reported missing. The hurricane also affected the US naval base at Guantanamo Bay, where 167 terror suspects are held. Preliminary hearings for the accused Al-Qaeda mastermind of the 2000 bombing of the USS Cole were delayed.

In Florida, authorities were on alert for tropical storm conditions, warning residents to prepare an emergency plan and supplies.

Schools in the state’s southern counties of Palm Beach, Miami-Dade and Broward were closed for the rest of the week.