Together, 风雨 (fēngyǔ - wind and rain) is a common metaphor in Chinese for difficulties, trials, and tribulations. 同舟 (tóngzhōu - same boat) creates the image of sharing a common fate. The combination paints a vivid picture of people united in a vessel, facing a storm, and relying on each other for survival. This visual metaphor makes the meaning—facing hardship together—incredibly memorable and poignant.
This idiom is formal and carries significant emotional weight. It is not used for minor inconveniences.