Learn Croatian: Na moru je često vjetrovito. - At the seaside it is often windy.

U moru literally means inside the water (like swimming). When talking about being at the coast or at the seaside, Croatian uses the preposition na (on) with the locative case, making it na moru.

Why does the word "more" become "moru" here?

Because it follows the preposition na to show a static location. This requires the locative case. The noun more (sea) is a neuter word, and its locative ending is -u, changing it to moru.

Where is the word for "it" in this sentence?

Croatian doesn't use a filler subject like "it" for weather phrases. While English requires "it is", Croatian simply uses the verb je (is) along with the describing word.

Why does the word "vjetrovito" end in "-o"?

For general statements describing the weather or an environment (like "it is windy"), Croatian uses the neuter singular form of the adjective, which ends in -o. There is no specific noun it needs to match here.