944mm 26/27 July : The reasons

1. LP off the Orissa coast
2. LP in central India
3. Western disturbance in the Arabian Sea
4. An unprecedented, huge "cloudburst over Santacruz" area in Bombay

The first three are the usual met-office type ones. The last one perhaps is the most significant. This probably led to the unusually heavy rains.

The destruction, however was due to:

1. Ineffective police functioning (traffic and directing people/railways/transport).
2. Poor civic management by BMC.
3. Unplanned construction activities of roads and new buildings over the year - The Land Mafias. This blocked the major drain networks at key points leading to widespread flooding. What else could be the reason, if even after 24 hrs. of the rain, the water had still not receded.
4. Ineffective "Disaster Management Cell". I dont know why they set up one, a few years back. Votes, I guess.
5. Total lack of communication by the police/BMC/Railways/BEST.
6. People (the new ones whove come to Bombay) making foolish decisions about their travel on Tuesday and Wednesday (like taking their cars out etc. , expecting trains etc., expecting that the routes theyve decided to take would be 'dry'. For example simple logic tells that if a place like Kala Nagar has 10 feet of water, then Kurla etc. would obvioulsy have more. But then this reasoning can be done only by someone who has stayed here earlier.
7. Rumour mongering. Self styled information givers to gain immediate points (e.g. "Boss, trains are running normally", etc. Each such unconfirmed statement would have led to at least 100 persons rushing to the stations for a sure-shot mis-adventure later. Thats anyway what happened. And when you think that each of these 100 would in turn misguide 100 more, then soon you cover most of our 15 million. Or at least 8 million that would have been out on Tuesday afternoon.

And when one gets panicky - it leads to further illogical and disastrous actions. Cant help it.