The nearest approach is 0.988x Lunar Distance (379,868 km), 60 Earth radii out. The size is very roughly 6.7 meters, 22 feet. If it hit the atmosphere, the airburst would be about 5 kilotons. Airbursts like that happen every few years. https://en.wikipedia.org/wiki/Meteor_air_burst#After_1900

Is it possible that one day a dinosaur extinction size asteroid will be annouced on a collision course?

Is there some reason we would already know, or can these things just suddenly show up?

It seems like every few months we find out our orbit is far more crowded than we thought.