UPDATE 1-U.S. Gulf storm not hurting offshore oil output

(Adds Accuweather forecast paragraph 4)

HOUSTON Oct 2 (Reuters) - U.S. Gulf of Mexico oil and natural gas producers said on Tuesday that stormy weather west of the Florida Keys was not expected to impair offshore production, which provides one-quarter of U.S. oil and 15 percent of U.S. natural gas.

The system, which was producing gale force winds, could form a subtropical or tropical cyclone on Tuesday or Wednesday, the National Hurricane Center said on Tuesday.

"Right now, we don't anticipate any impact on our operations," said Louisiana Offshore Oil Port spokeswoman Barb Hestermann.

Accuweather Inc. said the system was expected to enter by Wednesday and Thursday an area of the Gulf that will allow the development of a subtropical or tropical storm. The storm was expected to approach the coasts of Louisiana or Texas by Thursday night.

Anadarko Petroleum (APC.N), BP Plc (BP.L) among other companies said they would continue to monitor the storm's progress in the Gulf.