Tropical Storm Dorian officially became Hurricane Dorian on Wednesday, its sustained winds topping 75 mph as it bore down on Puerto Rico and St. Thomas in the Virgin Islands. Forecasters are now warning the storm will strengthen into a dangerous Category 3 hurricane as it nears the U.S. mainland.

Tropical Storm Dorian strengthened into a hurricane Wednesday afternoon near the U.S. and British Virgin Islands.

Residents there and in nearby Puerto Rico are facing heavy rain and strong winds, while forecasters are raising expectations for a Florida landfall this weekend for what may be a major hurricane event.

Dorian's center was near the island of St. Thomas when the National Hurricane Center announced the storm has sustained maximum winds at 75 miles per hour, enough to become a Category 1 hurricane according to the Saffir-Simpson Hurricane Wind Scale.

Hurricane Dorian was hitting the Virgin Islands on Wednesday, and was expected to slam into the island municipality of Culebra in Puerto Rico before moving into warm Atlantic waters, where it may strengthen into a major storm threatening the Southeastern United States.

The compact storm has been maddeningly difficult to forecast, as tends to be the case with smaller, disorganized systems.