The storm’s maximum sustained winds were clocked at 80 mph (130 kph) with higher gusts. Its center was located about 165 miles (260 kilometers) east-southeast of the southeastern Bahamas and about 470 miles (755 kilometers) east of Camaguey, Cuba.
Hours earlier, Tropical Storm Nadine formed off Mexico's southern Caribbean coast and was moving inland across Belize. Heavy rain and tropical storm conditions were occurring over parts of Belize and the Yucatan peninsula.
A tropical storm warning is in effect for Belize City and from Belize to Cancun, Mexico, including Cozumel.
The hurricane center said Nadine was located about 20 miles (35 kilometers) east of Belize City, with winds of 13 mph (20 kph). Its maximum sustained winds were at 50 mph (85 kph).
Nadine was expected to move across Belize, northern Guatemala and southern Mexico through Sunday, the center added.
Neither system posed a direct threat to the United States, though it was somewhat unexpected that Oscar became a hurricane on Saturday, said Philippe Papin, a hurricane specialist at the National Hurricane Center.
“Unfortunately, the system kind of snuck up a little bit on us,” Papin said.