surf's up

Etymology
Originally used in surfing to say there are good waves for surfing and one should get ready to ride them. This likely resulted in the later idiomatic use: to get ready for something.

Phrase

 * 1) A phrase used in surfing when a nearby wave is passing.
 * 2)  It's time (to do something).
 * Yo, Harold! Surf's up! Those cars aren't going to wash themselves!