Hiroshima was 15 kt, 4.23 Mt is 282x that. Fortunately this thing is small enough that it would burst at high altitude and only do minor damage on the ground:
It's about 10 times larger than the meteor that fell over Russia a few years back (the Chelyabinsk meteor [1]), so not too big in the grand scheme of things. It would not really have any major effects unless it hit near a populated area, which is very unlikely. If it did impact the Earth it would probably hit the Pacific ocean.
Also 4.23 Mt isnt a huge impact. Definitely not dinosaur killer right?