Alaska Airlines, which has been gradually expanding its service out of San Diego, announced Thursday that it will be launching a new nonstop flight to the Mexican resort destination Zihuatanejo. That is the highest number for any airport serving the San Diego airport, even exceeding Southwest Airlines, which operates the most overall flights of any air carrier here. Expect more nonstops as Alaska continues to expand its presence in San Diego, said Neil Thwaites, the airline’s regional vice president of California. “Part of our mission in San Diego is to increase direct connectivity for San Diegans to the places they want to go. “We’re committed to absolute growth in San Diego.