、。
I hope it clears up tomorrow.
Literal
Tomorrow, become-sunny [if-と] good [explanatory-んだ] [but-けど].
~といい expresses a wish or hope — literally 'if X, (it would be) good.' The trailing けど softens it, giving a wistful 'but...' tone, as if acknowledging the wish may not come true. んだ adds explanatory warmth. All together: 'I'm hoping it'll clear up, but... (we'll see).'