Instantly after Erin become a tropical depression , the National Hurricane Center gave out a tropical storm watch from Freeport , Texas to the United States\/Mexico border ; at the same time , the government of Mexico issued a tropical storm watch southward to Rio San Fernando . Immediately upon becoming a tropical cyclone , the National Hurricane Center issued a tropical storm watch from Freeport , Texas to the United States\/Mexico border ; at the same time , the government of Mexico issued a tropical storm watch southward to Rio San Fernando .