Complex sentence: September 2000 was generally unsettled, with wet periods between 14-19 (15th resulting in some flooding around Portsmouth and Southsea as a pumping station at Eastney failed) after 58mm of rain fell in 4.5 hours, being the heaviest rain since 1986 in the area.
Split into simpler sentences: September 2000 was generally unsettled, with wet periods between 14-19. This resulted in some flooding on the 15th around Portsmouth and Southsea as a pumping station at Eastney failed after 58mm of rain fell in 4.5 hours, being the heaviest rain since 1986 in the area.