You need to be free on a very specific day to take advantage.

Colorful Houses Line San Sebastian Street in Old San Juan, Puerto Rico
Credit: Brian Overcast / Alamy

On Wednesday evening, JetBlue announced a new flash sale, with tickets to 20 destinations available for as little as $20 one-way.

These cheap seats are only on specific flights — like a $30 ticket from Boston to Washington, D.C. on Flight 57, which departs on June 21 at 6:05 a.m.

New Yorkers, for example, can take a trip to either Orlando or Maine for $50 or $30, respectively. But these tickets are only valid on flights that depart on the evenings of June 17 and June 18.

Travelers can find these ridiculously low fares from a number of cities across the country, including Anchorage, Detroit, Fort Lauderdale, and Hartford (spontaneous Connecticut-based fliers can spend July 4 on a $60 flight to Puerto Rico). And you don't even need a passport.

The sale ends when the tickets run out, and JetBlue indicated that fares may only be available for less than an hour. If you don’t see something that works for you now, follow @JetBlueCheeps on Twitter and watch out for the hashtag #JetBlueFlashFares.