Under the influence of low pressure area, very heavy to extremely heavy rain recorded at various places in Thane, Raigad and Mumbai. On 29th today Mumbai is experiencing extremely heavy rainfall. Santacruz already recorded 298 mm from 0830 hours IST to 1730 hours IST which is the highest recorded this season with Colaba 65 mm. Kurla recorded highest 300 mm by 1730 hours IST.
Article source: WeatherView.in
Low Pressure Area & Convergence Zone
The main reason of the rain is the presence of low pressure area over South Madhya Pradesh. The heavy rain event over Mumbai is due to the vorticity effect which is the curving of winds (shown as a black line in the figure below). In technical terms it is a convergence zone of wind as well as moisture content. The low (1) is the position on 28th August and low (2) is the position by 30th August 2017 under which South Gujarat and Saurashtra will be under grip of heavy rain.
To watch the animation version with respect to above explanation click here
By the evening of 29th August the patch of clouds shifted northward causing heavy rains to the north of Mumbai such as Virar, Palghar and Dahanu. Thereafter it will move over South Gujarat and Saurashtra on 30th & 31st August 2017.
Below are the rainfall recorded at various places with 15 cm & above at 0830 hours IST on 29th August 2017:
Pen – 260 ; Nagothane – 203, Mhasala – 213, Dahanu – 195 Colaba (Mumbai) – 151.8, Mandangad – 175,
Today on 29th districts of Thane Raigad and Mumbai will experience extremely heavy rain. The rain over Mumbai will start receding from late morning of 30th.
On 30th Saurashtra and South Gujarat will experience very heavy to ext heavy and 31st onwards moderate rain till 02nd Sept.
Rainfall category in milimetres as per IMD:
64.5 to 124.4 Heavy
124.5 to 244.4 Very heavy
Above 244.5 Extremely heavy
If the amount is very very extremely high than it is Exceptionally heavy.