Complex sentence: The season produced 19 tropical depressions, of which 12 attained tropical storm status; one tropical storm was operationally classified as a tropical depression, but was reclassified in post-analysis.
Split into simpler sentences: The season produced 19 tropical depressions of which 12 attained tropical storm status. One tropical storm was operationally classified as a tropical depression but was reclassified in post-analysis.