Storm Seas

Oceans are immobile as are many of its bodies of water—but not all. There are whole seas that gradually move from one region to another, the forces of supernatural planetary energies in the atmosphere creating constantly raining storm patterns pushing ever further in one direction. Movement against the direction a storm sea is traveling is halved. Ability checks made to move in the same direction have advantage, and ability checks made to move in the opposite direction have disadvantage.