On 26 July 2005, around 2:00 p.m. the Mumbai Metropolitan Region was struck with a heavy storm. The Indian Meteorological Department station in Santacruz had recorded a record 944 mm. of rain for the 24 hours ended at 08:30 a.m. on 27 July (eighth heaviest ever recorded 24-hour rainfall ).  Local train movement came to a halt by 2:30 p.m. due to the water logging on the tracks, due to which, vehicular traffic intensity on roads increased. Water logging and submergence of certain low lying pockets of the region such as Dharavi, Bandra-Kurla Complex, Chunabhatti, Chembur, Ghatkopar, Milan Subway and Sion either slowed down traffic, or brought it to a grinding halt.

The situation worsened when the cellphone networks went down around 5 p.m. Land-lines of M.T.N.L. were also only partially functional. Adding to the chaos was the lack of public information. Radio stations and many television stations did not receive any weather warnings or alerts by the civic agencies.  The Powai Lake had started overflowing at 4 p.m. and discharged 5.95 million cubic meters of water into the Mithi River. The rainfall hydrographs of 26 & 27 July later revealed that two flood waves were generated in the streams and river basins of Mumbai, one between 2:30 & 20.30 p.m.- coinciding with the high tide period and another between 8 and 10 p.m. Normally, the second wave would have harmlessly drained because of the prevalent low-tide. But that did not happen because the accumulated water from the first flood wave had yet not flushed out effectively during the ebb period because of a choked drainage system. The result was that the flood situation kept on aggravating throughout the night. There was some relief in sight only when the second ebb period commenced at 6 p.m. on 28 July.

Due to submergence of the power stations and substations, Suburban power supply was suspended from the evening of 26 July and it was restored only after the flood waters receded. As many as 5,000 people were killed in the floods across the state of Maharashtra, many of them in Mumbai

Reference:

http://www.historyorb.com/day/july/26?p=2

http://en.wikipedia.org/wiki/Maharashtra_floods_of_2005

http://floodlist.com/asia/mumbai-floods-mithi-river

http://www.ndtv.com/photos/news/26july-2005-the-day-mumbai-stopped-11000#photo-138088