Southwest periodically make flights for further in the future available. You can now book flights until August 5, 2019. On February 7, 2019 the schedule will be extended again for flights until September 2, 2019. Still no Hawaii flights unfortunately.
Southwest has a pretty good cancellation/refunds policy, depending on the fare you’ve booked you’ll either receive a credit towards a future flight(Wanna Get Away) or cash refund (Business Select or Anytime – returned to credit card if you used one). That means it’s often best to book flights as soon as they become available and periodically check to see if the price has decreased, if it has you can click ‘change flight’.
Thanks for the reminder! I had completely forgotten!