Agh, that's awful. I forgot my umbrella. Let's find some shelter from this rain.
I don't have my/an umbrella. Let's find somewhere dry.
ーAgh, that's awful. I forgot my umbrella. Let's find some shelter from this rain.
「あ〜最悪。傘忘れた。どこかで雨宿りしよう」
to forget one's umbrella で「傘を忘れる」
to find some shelter from this rain で「雨をしのぐところを見つける」
ーI don't have my/an umbrella. Let's find somewhere dry.
「傘持ってないよ。雨宿りしよう」
don't have one's/an umbrella で「傘を持っていない」
to find somewhere dry で「どこか乾いているところを見つける」
ご参考まで！
カナダ 
