July 22 (Bloomberg) -- Tropical Storm Dolly strengthened over the Gulf of Mexico and may become a hurricane before making landfall in the next day near the Texas-Mexico border, the U.S. National Hurricane Center said.

Forecasters said the storm is unlikely to affect oil and natural gas operations in the Gulf, home to more than a quarter of U.S. oil production.

Dolly's maximum sustained winds have strengthened to 65 miles (105 kilometers) per hour, from 50 mph yesterday, the agency said in an advisory on its Web site at about 8 a.m. Miami time. The storm was 265 miles southeast of Brownsville, Texas, and moving toward the west-northwest at 13 mph.

``Additional strengthening is forecast, and Dolly is expected to become a hurricane prior to landfall,'' the agency said. Hurricanes have maximum sustained winds of at least 74 mph.

Dolly prompted authorities to issue hurricane warnings yesterday and advise boat-owners to make preparations for the storm.

A hurricane warning is in place along a 300-mile stretch of coast from the San Fernando River, Mexico, to Port O'Connor in Texas, and a tropical storm warning is in effect from north of Port O'Connor to San Luis Pass and in Mexico from La Pesca to south of the San Fernando river.

``Preparations to protect life and property should be rushed to completion,'' the center said.

Off the East coast of the U.S., Tropical Storm Cristobal accelerated over the Atlantic and will probably weaken, the U.S. center said.

The system, with 60-mph winds, was about 485 miles northeast of Cape Hatteras, North Carolina, and 450 miles south- southwest of Halifax, Canada, the center said in a separate advisory.

Cristobal was moving northeast at 21 mph and forecast to speed up and turn toward the east-northeast.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: July 22, 2008 08:29 EDT