About this phrase

Cóta is a masculine noun that means coat.

Báisteach is a feminine noun that means rain. It is in the gentitve case here (báistí) because it is the second noun in a two-noun cluster.

Thus, cóta báistí: raincoat.

Cóta is lenited here because of the preceding possessive adjective, do: your.

Thus, do chóta báistí: your raincoat.