I've applied previously and got this e-mail today:

Southwest Airlines will be opening our pilot hiring window September 12th and remain open for approximately two weeks. To express interest in Southwest Pilot positions, please go to Southwest Airlines Careers. Once there, click “View All Job Postings” and express interest in the open pilot requisition by uploading your resume and answering the prescreening questions. Please note, an applicant only needs to apply one time on the Southwest Airlines Careers website.

Having a profile on Pilot Credentials will NOT make you a Pilot candidate for consideration; you must also take the steps above to express interest through Southwest Airlines Careers. If you previously applied through southwest.com during our last hiring event, it is still necessary to complete this step to be considered.

After completing the steps above on Southwest Airlines Careers, please also review and update your existing profile at https://swa.pilotcredentials.com/ . Some areas on that website have changed and it is important that your profile information is current, complete and accurate.

Interviews will be granted on a qualifications review and competitiveness. Potential training class dates are tentatively scheduled beginning the first quarter of 2014.

Sincerely,
Southwest Airlines