Tropical Storm Bret chugged toward the eastern Caribbean on Tuesday as forecasters warned it could strengthen into a hurricane before approaching a region rushing to prepare itself for an unusually early storm.

Bret had maximum sustained winds of 65 kph and was moving across the Atlantic Ocean at 28 kph. It is expected to strengthen into a hurricane in coming days but then weaken ahead of its approach to the Lesser Antilles, according to the National Hurricane Center in Miami.

The storm is expected to pummel some eastern Caribbean islands on Thursday and Friday at near hurricane strength.

“Both the atmospheric and oceanic environment look conducive for strengthening during the next couple of days with low shear and abnormally warm ocean waters,” the centre said.

Dominica’s meteorological service said Tuesday that the storm poses a “high threat” to the island and warned of landslides, flooding, and waves of up to 4 metres.

Meanwhile, the hurricane centre urged people in the Lesser Antilles, Puerto Rico and the Virgin Islands to closely monitor the storm and have their hurricane plans in place.

“Given the larger than usual uncertainty in the track forecast, it is too early to specify the location and magnitude of where these hazards could occur,” the centre said.

Vertical shear and drier air are expected to later weaken Bret as it swirls through the central Caribbean region, potentially taking aim at southern Haiti as a tropical storm.

The storm formed Monday – an early and aggressive start to the Atlantic hurricane season that began on June 1. It would be only the second hurricane to form in the tropical Atlantic in June in nearly a century, according to meteorologist Philip Klotzbach at Colorado State University. The previous hurricane was Trinidad, which formed in 1933.

A tropical disturbance with a 60% chance of cyclone formation is trailing Bret. No June on record has had two storms form in the tropical Atlantic, Klotzbach noted.

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.