The depression gradually tracked northwestward at 15 mph (24 km/h). Although the center of the depression was initially uncertain, it slowly strengthened and steadily organized. The depression attained tropical storm status late on August 20, upon which the storm was named "Lester". The cyclone continued to the northwest, and passed directly over Socorro Island on August 21. By early the next day, an eastward moving trough weakened the ridge to its north, resulting in a to turn to the north. Around this time, forecasters at the National Hurricane Center predicted the storm would not strengthen to hurricane intensity before making landfall. Despite this, Lester intensified into a hurricane late on August 22 while located about 240 miles (385 km) west of La Paz in Baja California Sur.