Complex sentence: Since records began in 1928 the wettest month has been September 1939 with, part of the wettest year with and featuring on 5 September the wettest day with from the remnants of a rare Gulf of California hurricane.
Split into simpler sentences: Since records began in 1928 the wettest month was September 1939 with which was part of the wettest year with and featuring on 5 September the wettest day with. The moisture was due to the remnants of a rare Gulf of California hurricane.