HOUSTON (Reuters) - U.S. Gulf of Mexico oil producers on Saturday evacuated offshore facilities as a tropical storm brewing off the Florida coast was forecast to strengthen into a hurricane and threaten the prime oil region.

Chevron Corp <CVX.N> and Murphy Oil Corp <MUR.N> on Saturday started removing workers from offshore oil and gas platforms. Royal Dutch Shell, BHP, BP and Hess Corp said they were monitoring the storm and prepared to take action if needed.

Tropical storm Sally crossed the tip of Florida overnight and moved into the eastern Gulf of Mexico. The latest forecast by the National Hurricane Center calls for its maximum sustained winds to reach 80 miles per hour (129 kph) ahead of landfall next week.

Chevron has begun evacuating all staff from its Blind Faith and Petronius platforms and initiated shut-in procedures, a spokeswoman said, while production at its other offshore platforms was unaffected.

Murphy Oil was preparing to evacuate non-essential personnel from its most easterly facilities and monitoring the storm for potential impact on other properties, a spokeswoman said.

U.S. Gulf of Mexico offshore oil production accounts for about 17% of U.S. crude oil production and 5% of total U.S. natural gas production. As much as 1.5 million barrels per day of oil output was shut last month as Hurricane Laura tore through the Gulf of Mexico.

Sally was forecast to strengthen in the next several days and head for an area between southeastern Louisiana and Alabama.

If Sally becomes a hurricane, it would be the second to hit the U.S. Gulf Coast in less than a month. Hurricane Laura struck Louisiana with devastating, 150 mph winds, leveling coastal towns and putting two oil refineries out of commission for weeks.

(Reporting by Gary McWilliams; Editing by Daniel Wallis and Leslie Adler)