Surf's Up: 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.
Last year, my wife and I went to a town in northern Philippines noted for surfing. It was a ton of fun watching surfers attack the waves. I took the photo above showing one of he good surfers riding a small wave.
Thanks Brod. I must confess I am the same way at home. I wake up early enough - 5 am sometimes even 4. But I go back to bed and wake up closer to 11. But when we are on a trip I am a very early riser. I don't want to wait any daylight hours. LOL
Seriously though, I wish I learned how to surf when I was younger. But at that time we never thought of surfboards. I did a few escapades, "borrowing" a small bangka from the neighbors, rowing out to sea to the sandbars a few miles away from shore. One time the weather changed so sudden I was deathly scared and rowed back to shore like a banshee