Before you do anything else, cruise around outside the of walls of the tower to find the fish guy to have this place marked on your Sea Chart.
Now it's time to go after Ganon, but first you can learn a new song.
Learn the Ballad of Gales
Sail around to different squares looking for the giant cyclone. I found it at Mother & Child Isles, one square southeast of the Forsaken Fortress. When you find it, get caught in it.
Nintendo Gallery Note: This is your only chance to get a picture of Cyclos. Take a picture of the guy at the top of the cyclone as soon as you possibly can. Just get a picture of his little cloud and any part of his body that you can see. It doesn't matter if he's facing the camera or not. Once you defeat Cyclos, you can't get his picture again. You run the risk of getting warped somewhere while you try to take the picture, but you can always find him again somewhere if that happens. When I got warped the first time I tried, the cyclone was still at Mother & Child Isles. Remember not to save until after you've successfully gotten his figurine to make sure you didn't mess up the shot.
Once you have Cyclos's picture, shoot him with arrows. You can't lock on, so just do your best to aim. Repeat until the cyclone stops. You'll learn the Ballad of Gales, which makes sea travel much easier.
Nintendo Gallery Note: Warp to the Forest Haven and have your pictographs made into figurines. Then, if you want to be sure to get the next few figurines, save now, and be prepared to not save until after the next part.
Now it is time to go to the Forsaken Fortress. Don't warp to the top left warp spot. It puts you into a closed island that you can't sail out of. You can get an upgrade there, but I will describe that later. Instead warp to Tingle Island, which is southwest of Windfall. Then set the wind northwest and head for the Forsaken Fortress. Watch out for warships and glowing barrel bombs on the way.