A hurricane watch was issued as Tropical Storm Bret threatens to rip through Caribbean islands.

The storm was located about  320 kilometres (200 miles) east of Barbados on Thursday morning and was moving west at 24 km/h (15mph). It had maximum sustained winds of  110 km/h (70mph), just below the 119km/h (74mph) winds of a Category 1 hurricane.

The storm was expected to start affecting islands in the eastern Caribbean later in the day, according to the National Hurricane Center in Miami.

A special aircraft dispatched to investigate the storm on Wednesday found that Bret had grown a bit bigger, with tropical-storm-force winds extending outward up to 165km (105 miles) from its centre, according to forecasters.

Airports, businesses, schools and offices were closing in St Lucia and Dominica as forecasters warned of torrential downpours, landslides and flooding.

“Protect your lives, property and livelihoods,” urged St Lucia Prime Minister Philip Pierre.

Andre Joyeux, director of St Lucia’s Meteorological Services, said Bret is expected to cut directly through the island.

“We are hoping that persons take heed,” he said.

The hurricane centre said that there are up to three centimetres (10 inches) of rain forecast for the French Caribbean island of Guadeloupe south to St Vincent and the Grenadines, including Barbados. Waves of up to four metres (13 feet) were also forecast for Guadeloupe, according to local meteorologists.

Bret is expected to lose strength once it enters the eastern Caribbean Sea, and it is forecast to dissipate by the weekend.

However, the Caribbean is closely watching a tropical depression that is trailing Bret and has a 90 percent chance of formation.

If the depression strengthens into a storm, it would be the first time since record-keeping began that two storms formed in the tropical Atlantic in June, according to meteorologist Philip Klotzbach at Colorado State University.

The National Oceanic and Atmospheric Administration has forecast 12 to 17 named storms for this year’s hurricane season. It said between five and nine of those storms could become hurricanes, including up to four major hurricanes of Category 3 or higher.