(CNN) The year's first Atlantic hurricane weakened Saturday morning into a tropical storm, but Caribbean islands struck by last year's devastating hurricanes are still on alert.

Beryl remained very small, moving west-northwest at 17 mph with maximum sustained winds of 50 mph, shy of Category 1 status, according to an advisory issued at 5 p.m. ET by the National Hurricane Center.

Though the storm's intensity could still fluctuate unpredictably, its chances of regaining hurricane strength before reaching the Lesser Antilles, the arc of islands from the US Virgin Islands to Grenada, have dropped significantly, CNN meteorologists said.

Beryl is due to reach that zone sometime late Sunday, the hurricane center said, at which point it's likely to weaken into a tropical depression.

Later Monday the storm is expected to head south of the Virgin Islands and Puerto Rico, whipping the island with minimal tropical storm-force winds as it continues to weaken.