SAN FRANCISCO — Tropical Storm Hermine strengthened near the Gulf of Mexico Monday, raising concerns it could hamper oil-producing and refining areas.

The National Hurricane Center has issued a hurricane watch from the mouth of the Rio Grande northward to Baffin Bay in Texas.

The center of the storm is expected to approach the coast of northeastern Mexico or southern Texas Monday night, and Hermine “”could approach hurricane strength prior to landfall,”” the center said.

Hermine is about 205 miles south-southeast of Brownsville, Texas, and has displayed maximum sustained winds of 50 miles per hour, the center said.

If it remains below hurricane strength, “”then it poses little more than the threat of temporary disruption to (oil) refineries at Corpus Christi, Texas,”” analysts at J.P. Morgan & Chase Co. said in a note Monday.

Reformulated gasoline for October delivery ended down less than a penny at $1.92 a gallon Friday. Gasoline declined 1.6 percent last week. Markets are closed Monday in observance of Labor Day.

At the pump Monday, prices averaged $2.683 a gallon for regular gasoline, according to travel and leisure group AAA. That compares with $2.584 a year ago.

But the storm “”highlights how rapidly new threats can appear now that we are approaching the peak of hurricane season,”” analysts at J.P. Morgan said.

The Atlantic hurricane season began June 1 and will last till Nov. 30. Government forecasters have projected, with a 70 percent probability, 14 to 20 named storms and between eight to 12 hurricanes this year.

Forecasters are also keeping their eyes on the remnants of storm Gaston, located about 300 miles east of the northern Leeward Islands. The system is moving west and there’s a 70 percent chance of it becoming a tropical cyclone again in the next 48 hours, the National Hurricane Center said.

Historically, hurricane season peaks in mid-September. Two of the season’s storms, Danielle and Earl, have become major hurricanes.

Earl dissipated over Canada’s Eastern coast over the weekend. Earl had threatened the U.S. East Coast earlier in the week, but ultimately caused little damage.

Earl made landfall in southern Nova Scotia Saturday, hitting Halifax with strong winds and rain. One man died after falling out of his boat in Nova Scotia while almost 1 million were without power in the region, according to wire service reports.