Tropical Storm Fred has swirled toward the Dominican Republic and Haiti, with forecasters warning that heavy rains could cause dangerous flooding and mudslides.

After a quiet month of no named storms in the region, Fred became the sixth of the Atlantic hurricane season late on Tuesday as it passed by the US Virgin Islands and Puerto Rico.

Tropical storm warnings were discontinued in the US territories after pelting the islands with rain.

Power outages were reported in Puerto Rico, where Luma, the company in charge of the transmission and distribution system, warned those who depend on electricity for life-saving medical devices to activate emergency plans.

Here are the 5 AM AST Aug 11 Key Messages for Tropical Storm #Fred, which is currently approaching the Dominican Republic. More information: https://t.co/vbprzkjSVW pic.twitter.com/wtsCfTo0TR

— National Hurricane Center (@NHC_Atlantic) August 11, 2021

“Puerto Rico’s system … continues to be very fragile,” the company said, referring to the power grid Hurricane Maria destroyed in 2017.

Fred was centred 190 kilometres east-southeast of Santo Domingo, Dominican Republic early on Wednesday and moving west-northwest at 26km/h, the US National Hurricane Centre said.

It had maximum sustained winds of 65km/h.

The Dominican Republic, Haiti and central and eastern Cuba could get hit Wednesday, and people in Florida were urged to monitor updates.

Forecasters said the centre of Fred is expected to be near or over Hispaniola later Wednesday, move near the Turks and Caicos Islands and the southeastern Bahamas on Thursday, and move north of the northern coast of central Cuba on Friday.

Puerto Rico Governor Pedro Pierluisi said government agencies would close and officials noted that some gas stations had shut down after running out of fuel. The heaviest rain was expected to fall during the night, forecasters said.

Eight shelters were opened across the island, though officials said only about seven people had checked in by midevening.

“Do not wait until the last minute to mobilise,” said Nino Correa, Puerto Rico’s emergency management commissioner. “We don’t want to have fatalities.”

More than a month had passed since the last Atlantic storm, Hurricane Elsa, but this time of summer usually marks the start of the peak of hurricane season.

The hurricane centre issued warnings for Dominican Republic on the south coast from Punta Palenque eastward and on the north coast from the Dominican Republic/Haiti border eastward.

A watch was in effect for Haiti from the northern border with the Dominican Republic to Gonaives, Turks and Caicos Islands and southeastern Bahamas.

The storm was expected to produce rainfall of 5 to 10 centimetres over Puerto Rico and the Dominican Republic with up to 15cm in some areas.