Because of the storm, we had no choice but to stay home.
Literal
Storm [possessive-の] because us [topic-は] unavoidably home [at-に] were.
嵐の為 (because of the storm) uses 為 (ため) in kanji. やむなく (unavoidably/reluctantly) expresses having no choice — from 止む (to stop/cease) + なく (without). 家にいた (were at home) is the simple result.