Flooding was reported from Malad, Andheri, Versova, Dadar, Parel, Chembur, many parts of the key LBS Marg in the eastern suburbs, and Marol-Saki Naka belt.
Two important subways at Malad and Andheri were flooded, with about three feet of water, making them non-functional for the east-west traffic movement.
Local trains were delayed. Central Railway trains ran late by 20 minutes, Western Railway ones by 15 minutes, and trains on the Harbour Line by 30 minutes. Peak morning hour commuters and businessmen were left in a spot.
In the 24 hours preceding 5.30 a.m. Monday, South Mumbai recorded 9.04 cm rain, while the suburbs notched a staggering 18.01 cm rain in the past 24 hours, a weather bureau official said.
The forecast for Monday and Tuesday is "heavy to very heavy rains" in many parts of the coastal areas including Mumbai, with accompanying strong winds and advice to fishermen not to venture into the Arabian Sea.
The torrential, virtually incessant, rain since Saturday night has resulted in traffic moving at a snail's pace on the Eastern Express Highway, Western Express Highway, the Jogeshwari-Vikhroli Link Road, and other important roads and junctions.
Though Mumbaikars enjoyed the monsoon with parties and picnics during the weekend, the grim reality dawned on Monday, as schools reopened after the summer break and many office-goers returned to work.
The monsoon has also set in other parts of the state, offering welcome respite from water scarcity and intense heat wave conditions.
Till date, there have been 11 monsoon-related deaths in different regions across the state.