Here "one" refers to a mighty king who also represents his powerful army. Alternate translation: "the Lord sends a king with his powerful army" (See: [[rc://en/ta/man/jit/figs-synecdoche]])
A "storm of hail" or hailstorm happens when hard pieces of ice fall from the sky. Here it is a simile that refers to the enemy army that Yahweh will send to destroy the people of Samaria. (See: [[rc://en/ta/man/jit/figs-simile]])
The king and his powerful army destroying the people of Samaria and their city is spoken of as if the king will throw the people's garlands onto the ground. (See: [[rc://en/ta/man/jit/figs-metaphor]])