“Once by the Pacific” describes a gathering storm and ends with a dark vision of the destruction of the world. The speaker sees menace everywhere as the storm approaches. Some deeper, malevolent force is at work; things are not as they should be. In Line 1, for example, the ocean waves are not smooth and calm. Instead, the water is “shattered”; it seems broken and, therefore, disordered. In literal terms, waves "break" when they hit the shore, but the speaker implies a more frightening, dysfunctional shattering here. The use of the word “shattered” as the first significant word in the poem foreshadows what is to follow.

The alarmed speaker also experiences a change in sensory perception. His sight diminishes because of mist or fog; the scene is much noisier than usual too (“misty din,” Line 1). Worst of all, the speaker senses that the incoming waves are actively hostile. They intend to harm the land in a way that has never happened before (Line 4). This personification of the ocean waves gives the poem an apocalyptic tone. These waves are something more than sea water; they are a mighty, irresistible force, and they are not benevolent.