Tropical storm Rafael formed Monday in the Caribbean and will bring heavy rain to Jamaica and the Cayman Islands before strengthening into a hurricane and likely hitting Cuba, forecasters said.

Later in the week it also is expected to bring heavy rainfall to Florida and portions of the U.S. Southeast, according to the U.S. National Hurricane Center in Miami.

A tropical storm warning was in effect for Jamaica, and a hurricane watch was in effect for the Cayman Islands and for parts of Cuba, including the provinces of Pinar del Rio, Artemisa, La Habana, Mayabeque, Matanzas and the Isle of Youth. A tropical storm watch was issued for Villa Clara, Cienfuegos, Sancti Spiritus, Ciego de Avila, Camaguey and Las Tunas in Cuba.

A tropical storm watch was also issued for the lower and middle Florida Keys from Key West to west of the Channel 5 Bridge, and for the Dry Tortugas. The storm was located about 280 kilometres south of Kingston, Jamaica. It had maximum sustained winds of 75 km/h while moving north at 15 km/h, the centre said.

Storm could hit Cuba Wednesday

The storm was expected to move near Jamaica late Monday, be near or over the Cayman Islands late Tuesday as a hurricane and approach Cuba on Wednesday.

Most forecasts show the storm peaking as a Category 1 hurricane, "but conditions over the next few days will favour strengthening, so we'll need to monitor how quickly it organizes, and a stronger hurricane can't be ruled out," wrote Michael Lowry, hurricane specialist and storm surge expert, in an analysis Monday.

The timing could not be worse for Cuba, which last month suffered a collapse of its national electric grid, leaving an estimated 10 million people without power for several days. Many of the island's residents still face hours-long outages daily due to generation shortfalls.

Hurricane Oscar made landfall in Cuba around the same time as last month's blackout, throwing a one-two punch that has sapped precious resources, in a country already suffering from severe shortages of food, fuel and medicine.

Authorities said on Sunday they had evacuated more than 66,000 Cubans from far-eastern Cuba, in Guantanamo province, ahead of predicted heavy rains and flooding early this week. Soils in the province were already saturated by flooding and damage from Oscar, the government said. Plans were also under way to evacuate thousands of residents in Pinar del Rio province, on the island's far-western end.

The government encouraged residents, many still largely without communication because of power outages, to dial a government emergency phone number to follow the storm's progress.

Preparations underway in Cayman Islands

On Monday morning, the government of the Cayman Islands offered people sandbags and announced schools would close on Tuesday.

"Residents are urged to take immediate precautions to protect themselves and their properties," the government said in a statement.

Meanwhile, the Jamaica Observer newspaper reported a large landslide in a rural area north of the Kingston capital on Sunday that officials blamed on persistent rains ahead of the potential storm. No injuries were reported, but a couple of communities were left isolated.

Heavy rainfall will affect the western Caribbean with totals of seven to 15 centimetres, and up to 23 centimetres expected locally in Jamaica and parts of Cuba. Flooding and mudslides are possible.