In the Discworld series, written by Terry Pratchett, there's a group of magic users called witches who are down-to-earth, sensible people who do all the dirty work needed to keep life going, and they take care of the people and issues that fall between the cracks. Anywho, a number of them can see the future, and will tell people their futures for money.
However, most of the time people don't like what's actually in their future, and witches are either too blunt or not nice enough to sugar-coat what they see. Pratchett refers to such future-seeing witches as misfortune tellers.
Edit: as far as I know, this term is not used outside of Pratchett's writings. However, also as far as I know, there is no word in the English language to describe someone who reliably predicts minor misfortunes. Doomsayer or harbinger both kind of fit, in my opinion, but they suggest predictions of apocalyptic scale.