HOUSTON (Reuters) -Royal Dutch Shell and Chevron on Thursday began evacuating non-essential personnel from offshore U.S. Gulf of Mexico platforms ahead of a storm expected to enter the Gulf this weekend.

A storm brewing in the Caribbean Sea could become a major hurricane this weekend and strike the U.S. Gulf Coast by Sunday, the National Hurricane Center said. Hurricanes with winds of up to 111 miles per hour (178 km) are classified as major and can bring devastating damage onshore.

“This storm has the potential for rapid increases in intensity before it comes ashore” because of extremely warm waters off Louisiana, said Jim Foerster, chief meteorologist at DTN, which provides weather information to offshore oil and transportation companies.

Shell said evacuations covered all eight of its Gulf of Mexico properties and a floating production and storage vessel was being moved out of harms way. Chevron said its Gulf of Mexico oil and gas production remained at normal levels.

“Water temperatures are 85 degrees to 88 degrees Fahrenheit (29-31 C), that’s anomalously high, 3 to 5 degrees higher than it normally would be,” said DTN’s Foerster. A projected path over warm waters will result in heavy rains and flooding as it nears the central Gulf Coast, he said.

(Reporting by Gary McWilliams; editing by David Evans and David Gregorio)