jessica always warns me about my future.
As it's written, no, it is not. It lacks a subject. The only possible subjects that correspond to the verb is I, we, you,and they. The example is one pronoun short of being a sentence.
The direct object in this sentence is "us." The verb "warned" is directly affecting "us" by giving them a warning to stay on the ranch.
The captain warned the lookouts to be extra vigilant as a radio signal warned of possible enemy ships ahead.
The mother warned the daughter not to compromise her values.
The TV weather man warned that a storm, approaching from the west, was imminent.
The commanding officer warned his troops not to pillage the conquered city.
Drivers were warned of the adverse camber on the bend by the road signage.
The sign on the highway warned that you must yield to other vehicles.
The soothsayer warned Captain Bob not to travel the Atlantic Ocean for it is stormy.
The artesian aquifer lies deep below the earth's surface. "Don't go down to the aquifer," warned Dr. Warren. "The last couple who went didn't come back!"
when anushka was explaining the whole thing in length , the teacher warned her sternly not to beat about the bush
The doctor warned him that too many hamburgers would lead to a heart attack.