。
I hope it's sunny tomorrow.
Literal
Tomorrow [topic-は] clear-up [if-と] good [quotative-と] think.
晴れるといいと思う — 'I think it would be good if it clears up.' Casual, slightly less assertive than the polite 思います variant. Wraps a wish inside an opinion clause: the conditional ~といい sets up the wish, and ~と思う converts it from a direct hope into a stated opinion.