When he first sets sail, they "got under way with a mere breath of wind, and for many days stood along the eastern coast of Java, without any other incident to beguile the monotony of our course" (4). In other words, things are peachy keen and it looks like smooth sailing… for now.
Then things take a turn for the ominous:
One evening, leaning over the taffrail, I observed a very singular, isolated cloud, to the N. W. It was remarkable, as well for its color, as from its being the first we had seen since our departure from Batavia. I watched it attentively until sunset, when it spread all at once to the eastward and westward, girting in the horizon with a narrow strip of vapor. (5)
Sure, this is a pretty stock and standard cloud formation, and we bet any old salt on the sea is going to see it and scoff. And yet the words Poe chooses—that the narrator "watched it attentively"—and the fact that it's the first cloud they've seen shout: this is not your average cloud.
And wouldn't you know? That cloud swirls itself up into a hurricane. But before that happens, Poe gives us a healthy dose of suspense and dread: "As night came on, every breath of wind died away, and a more entire calm it is impossible to conceive. The flame of a candle burned upon the poop without the least perceptible motion, and a long hair, held between the finger and thumb, hung without the possibility of detecting vibration" (5).
You can literally cut the tension with a knife. When you're reading Poe, you just know that if everything is that still, it's all about to hit the fan, big time. The coming hurricane marks the shift in the story from normal to paranormal.
Before the storm, our narrator's just a cranky codger on a cargo ship. Afterward, he's a reluctant passenger going along for a ride to the death. And that shift is reflected in the weather, too. As the narrator and the Swede head south toward their run-in with the galleon, "The sun arose with a sickly yellow lustre, and clambered a very few degrees above the horizon—emitting no decisive light. […] Just before sinking within the turgid sea its central fires suddenly went out, as if hurriedly extinguished by some unaccountable power. It was a dim, silver-like rim, alone, as it rushed down the unfathomable ocean" (7).
Unfathomable ocean, you say? Unaccountable power? In his descriptions of the sun and the ocean, Poe is upping the mystery ante in a major way, setting us up for the supernatural arrival of the galleon.
And arrive it does. After being "enshrouded in pitchy darkness" (8), the narrator and the Swede stumble upon the galleon, looming above them on top of a wave. And what do they notice? The ship's relationship with the elements, of course:
But what mainly inspired us with horror and astonishment, was that she bore up under a press of sail in the very teeth of that supernatural sea, and of that ungovernable hurricane. (9)
Check it out. The whole time he's been sailing—or shall we say drifting?—with the Swede, the elements have been reflecting their dire predicament. In other words, Poe has been using the weather, the sea, and the sun to mirror the situation. But now, the galleon is mastering the elements—controlling and using them to its own devices. In a way, this makes the appearance of the ship even creepier. While the weather has been terrifying and ominous all the way through the story, exerting total control over our narrator, he's now managed to stumble upon the one force that can master the weather itself. Yeah, this can't be good news.