Here "blood" is a metonym for injury and death. Alternate translation: "I will judge him by causing him to be sick and by sending soldiers to kill him" (See: [[rc://en/ta/man/jit/figs-metonymy]])
It may be helpful to change the order of this sentence. Alternate translation: "I will rain down overflowing rain and hailstones, fire, and burning sulfur upon him and his troops—and on the many nations with him"