Input (grade 13): As it moved slowly across the Gulf of Mexico, Carla steadily strengthened to its peak of 175 mph (280 km\/h) winds (Category 5 intensity) on September 11.
Output (grade 12): As it moved slowly across the Gulf of Mexico, Carla got stronger to its peak of 175 mph (280 km\/h) winds (Category 5 intensity) on September 11.