Some Gulf of Mexico oil and gas operators began evacuating workers from offshore facilities but kept production flowing on Thursday as a low-pressure system threatened to strengthen into a cyclone.

The U.S. National Hurricane Center said Thursday morning that a weather disturbance in the northwestern Caribbean Sea had become less organized overnight and had a 50 percent chance of becoming a tropical cyclone in the next 40 hours, down from a 70 percent chance.

Marathon Oil Corp. said on Thursday that it was evacuating workers not essential to production from its Ewing Bank platform, which can produce up to 9,700 barrels per day of oil and 8.2 million cubic feet per day of natural gas. Such workers would include cooks and maids.

“Marathon Oil’s operated production has not been impacted at this time,” spokesperson Lee Warren said.

BP Plc said it was evacuating nonessential workers from oil and gas platforms. It has four platforms in the central Gulf, including Thunder Horse, the biggest in the world.

The company said it had temporarily halted contracted drilling rigs, but platforms were still working.

“Oil and natural gas production at all BP-operated platforms remains online at this time,” the company said.

Destin Pipeline Co. LLC also said pipelines in the Gulf of Mexico operated by BP were evacuating nonessential workers. The company said it would continue to accept natural gas flows as weather conditions permit.

Other companies said they were monitoring the storm.

(Reporting by Kristen Hays and Erwin Seba in Houston and Eileen Houlihan in New York; Editing by Terry Wade and Lisa Von Ahn)