It can only hit the side of the planet facing the sun at the time, unless (and heavens forbid) it was some sort of massive coronal burst that was wide an deep enough to bombard the earth for a complete 24 hours.

Usually the initial bombardment that would be powerful enough to take radio signals down isn't very long, and thus can only hit one side.

You can only talk in written terms about hemispheres with a common point of reference. That reference is the axis, with both hemispheres centred on the axis and forming the equator in the middle. Once you have told the reader it affected both hemispheres you need to establish the east-west sections. Which they do by mentioning the Americas and Pacific.

At one time it was common to see the use of longitudinal and latitudinal spans, but most people are not as familiar with the lines since globes are not as common and digital maps don't usually display them.