A surface explosion will produce much more early fallout than a similarly sized air burst where the fireball never touches the ground. This is because a surface explosion produces radioactive particles from the ground as well as from the weapon. The early fallout will drift back to earth on the easterly prevailing wind, creating an elliptical pattern stretching from ground zero out into New Jersey. Because the wind will be relatively light, the fallout will be highly concentrated in the area of Manhattan just to the east of the blast. Predicting levels of radiation is difficult and depends on many factors like bomb size, design, the ground surface and soil type.
