A prophetess is a woman who people believe has been sent by God to lead them — a female prophet. In the Bible and in religious history you meet named prophetesses: women who speak for God, warn a people, or guide them. The core is that calling, not a night-market guess about next week. The word is old and rather formal. Though actually, older English liked a special -ess form for the woman (as with actress), and prophetess still lives in religious writing and in older translations. Many speakers today just say prophet for a woman as well, especially in ordinary news, and that is now the more usual choice. It is not a general word for any woman who claims to see the future; if you use it that way as a joke, the religious colour is still sitting in the word.