Updated at 11:12 p.m. ET
Puerto Rico is now under a hurricane watch because of Tropical Storm Dorian, meaning the island could see dangerous conditions within 24 hours.
Dorian's maximum sustained winds remain near 50 mph with higher gusts, according to the National Hurricane Center. As of 11 p.m. ET, the compact storm was about 275 miles southeast of Ponce, Puerto Rico.
"Slow strengthening is forecast during the next 24 hours," the NHC says, "and Dorian is forecast to be near hurricane strength when it approaches Puerto Rico on Wednesday."
Anticipating the storm, President Trump has approved a federal emergency declaration for Puerto Rico, authorizing disaster relief aid.
Dry air around Dorian has tamped down the storm's strength. And the hurricane center says the system could also weaken when it passes over the higher terrain of Puerto Rico and Hispaniola.
Questions remain about what Dorian might do after that point, but it seems likely that the storm will persist and even strengthen as it moves to the northwest, toward the U.S. mainland.
"Tropical storm conditions are expected and hurricane conditions are possible in Puerto Rico on Wednesday. Tropical storm conditions are expected in the U.S. Virgin Islands on Wednesday. Tropical storm conditions are expected in portions of the Dominican Republic late Wednesday and Thursday," the National Hurricane Center says.
"On the forecast track, the center of Dorian will move across the northeastern Caribbean Sea overnight, pass over or near Puerto Rico on Wednesday, and move near or just east of eastern Hispaniola Wednesday night," the National Hurricane Center report adds. "Dorian is forecast to move near or to the east of the Turks and Caicos and the southeastern Bahamas on Thursday night, and near or to the east of the central Bahamas on Friday."
The longer-range forecast calls for Dorian to reach Florida over the weekend, where it could drop 3 to 5 inches of rain.
Despite maintaining a compact, roughly circular shape, Dorian has not developed a well-defined core. It began the day Tuesday as it did Monday, with tropical-storm-force winds that extend outward for only 45 miles from the center.
Dorian isn't currently likely to strengthen into the sort of fearsome cyclones that recently ravaged Puerto Rico and other islands, but it still poses a threat to vulnerable areas because of heavy rains and high winds. It's expected to drop 2 to 4 inches of rain in Puerto Rico, St. Croix and the Dominican Republic, with 6 inches of rain possible in isolated spots.