Deep — One affliction comes immediately after another, as if it were called for by the former. A metaphor taken from violent and successive showers of rain; which frequently come down from heaven, as it were at the noise, or call of God's water spouts.
Related Commentaries of Psalms 42:7
Psalms 42:7
7 Deep calleth unto deep at the noise of thy waterspouts: all thy waves and thy billows are gone over me.