During the late evening of September 4, a large intense area of thunderstorm activity formed near the Guatemala-El Salvador coast. The thunderstorm developed a circulation about 24 hours later, and was thus upgraded into a tropical depression a few hundred miles south of the Mexican coast. Turning west-northwest over waters, the depression was upgraded into Tropical Storm Sandra early on September 7. By 0600 UTC September 8, winds had increased to 75 mph (120 km/h), and Sandra was upgraded into a hurricane. Sandra turned west, and quickly intensified, reaching Category 3 status later that day after bypassing the Category 2 stage. On 0000 UTC September 9, Sandra peaked in intensity with winds of 125 mph (205 km/h).