MIAMI (Reuters) - Tropical Storm Rafael formed over the eastern Caribbean Sea on Friday, triggering storm warnings for Puerto Rico, the U.S. Virgin Islands and several other islands, the U.S. National Hurricane Center said.

Rafael was centered about 125 miles west-southwest of the island of Dominica and was moving north-northwest at 12 miles per hour.

It had top sustained winds of 40 mph and was forecast to move on a northern path that posed no threat to the United States or the Gulf of Mexico, where U.S. oil and gas operations are clustered.

Storm warnings were also issued for Antigua, the British Virgin Islands, St. Martin, Guadeloupe and St. Lucia, alerting residents to expect storm conditions in some areas later Friday night.

The storm was expected to move east of Puerto Rico on Saturday and out over the open Atlantic Ocean. (Reporting by Kevin Gray; Editing by Eric Walsh)