You realize that "sinister" means "evil"? Few things feel evil about a bright sun -- unless perhaps you are lost in the desert without water.
The sun rose, bright and sinister.
Because sinister is an adjective, is must modify a noun, the sun. Make sure your sentence doesn't ready as though sinister described the rising of the run -- the comma takes care of that.
The adverb form is "sinisterly." (And you'd need "brightly" as well)