Southwest Airlines will begin offering daily nonstop service between San Diego and four other cities, to New Orleans, Seattle, Portland, Ore., and Orlando, Fla., starting next year.

The announcement was made via a "mystery gift" delivered to the city at Balboa Park, and opened by interim San Diego Mayor Todd Gloria.

Southwest, which already makes San Diego one of its key markets and the largest carrier in terms of the number of flights out of Lindbergh Field, is apparently looking to protect itself from another carrier, Delta Airlines, that recently announced nonstop flights to Seattle.

In November, Delta said it will commence four nonstop flights to Seattle starting June 2, 2014.

Southwest said the daily service to New Orleans begins April 8, while the nonstop service to Orlando, Portland, and Seattle begins June 8.

To gin up new customers, Southwest is offering discounted airfares one way of $89 to Seattle and Portland, and $149 one way to New Orleans and Orlando. Tickets must be purchased by Dec. 20 and travel restrictions apply.

The Business Journal is the premier business publication in San Diego. Every day online and each Monday in print, the Business Journal reports on how local business operate and why businesses leaders make the decisions they do. Every story is a dose of insight into how to run a better, more efficient, more profitable business.