expose for the background.. and then photoshop it! Of course, you would have to have the beach, catch it at the right time, the right tide, and the right light.
A lot of good post processing. The basic effect here can be done exactly as said above. Use the sun, or other light source behind your subject and expose for it.
take someone out on a date, woo them, get married, have 3 children, wait 14 years, take them to the beach, wait there for a few weeks until the light is nice, tell them to dance, expose for the sky.
It doesn't look like a huge amount of PP, most of that effect is achieved in camera by metering off the sky. It just looks like a contrast and saturation bump in post.
Yeah, expose for background close to sunset. You want the sun behind the subject. Then increase the contrast to enhance the silhouettes if needed and increase saturation and vibrance. Its really a lot simpler then it looks. Mostly it is good timing and use of light.