Well - a bit of blah blah - this tutorial assumes you have some drawing skills (I'm talking pencils) and a fair knowledge of Photoshop.
Since the whole picture would make for a very long and tedious tutorial I will split it into 3 parts- sky, water and land. Some of the parts have to be drawn as a whole though so I am including those here even if it's not just sky...
Now to begin you will need some inspiration - look out the window, switch the TV to National Geographics or get that postcard mom sent you from the islands:)
My inspiration comes from from the beaches in my birth town.