The fourth named storm of the 2011 season developed over the southern Gulf late Wednesday afternoon.
A tropical storm watch means tropical storm conditions are possible in the area within 48 hours. The watch is in place from Port Mansfield northward to near San Luis Pass.
Late Wednesday night, the storm was about 675 miles (1,085 km) east-southeast of Corpus Christi, the center said. It was moving to the west-northwest at nearly 12 mph (19 kph).
"Some strengthening is forecast during the next 48 hours," the center said. An Air Force reconnaissance plane is scheduled to check the storm at daybreak.
If it continues on its projected path, the storm should approach the coast of the northwestern Gulf of Mexico on Friday.