Tropical Storm Don, the fourth named storm of the Atlantic hurricane season, was churning northwestward across the southern Gulf of Mexico toward the Texas coast.

A tropical storm watch was in effect for the coast, from the mouth of the Rio Grande River to west of San Luis Pass, the U.S. National Hurricane Center said early Thursday.

At 7 a.m. CDT (1200 GMT), Don was packing maximum sustained winds of 40 miles per hour (65 kmph) and was located about 545 miles (875 km) east-southeast of Corpus Christi, Texas.

The center of Don should move through the southern and central Gulf of Mexico later Thursday and approach Texas on Friday.

"Some strengthening is possible during the next 48 hours. An Air Force Reserve hurricane hunter aircraft is en route to investigate Don," the Miami-based hurricane center said.

Don's current path would take it near oil and gas operations in the western and west-central part of the Gulf, mostly avoiding the biggest concentrations of production platforms south of New Orleans, but near several coastal refineries.

Several offshore energy operators, including Shell Oil Co (RDSa.L), Apache Corp (APA.N), Anadarko Petroleum Corp (APC.N), have already started evacuating workers from production platforms, but have not undertaken measures to shut production yet. [ID:nL3E7IR2EB]

Refiners along the Gulf Coast, home to 40 percent of the nation's refining capacity, were also watching the system.

The Gulf accounts for 29 percent of U.S. oil production and 13 percent of natural gas output. About 30 percent of U.S. natural gas processing plant capacity also lines the Gulf Coast.

"Don is a small tropical cyclone. Tropical-storm-force winds extend outward up to 45 miles (75 km) from the center," the NHC said.

The U.S. government's weather agency has forecast an "above normal" 2011 Atlantic hurricane season, spawning six to 10 hurricanes of which around half could become major.