Vaughan's poem starts out on the open ocean, then moves to a road, a mountain, and finally a classroom. In each place, people are bracing for the same thing: a storm. The repeated line "A storm is gathering" works like a warning bell, and it keeps returning, growing more urgent each time.
The first three scenes feel like real weather, with sailors, drivers, and hikers all scrambling for safety. The last scene is different. Here the speaker says "we can only expect" the principal to announce that everyone must go to "safe areas." That detail suggests the storm may be more than weather. It could point to a different kind of danger that students are taught to prepare for, though the poem never says so outright.
The mood is tense and uneasy. The short lines and the repetition make the poem feel hurried, as if there's no time to stop. The speaker sounds resigned and watchful, waiting for the bad news to arrive. Ending on the bare line "A storm is gathering" leaves the threat hanging in the air.