The Low in the Bay, numbered BB-13, has moved West into Orissa. BB-13, will move West, into MP, and  restricted by the high pressure in the North.
It will track thru MP and weaken along its path, 

Friday: Heavy Rains to Watch out for: Central MP. Bhopal Districts.
Saturday: Western MP and adjoining North Maharashtra and parts of Eastern Gujarat.

City Forecasts:
Mumbai: Rainfall intensity and frequency decreasing. 
Friday. Partly cloudy day. Thunder clouds building up in the Eastern sky. Chances of drifting and bringing rain in some parts of city by evening. Rain amount expected: 10-12 mms average.
Saturday/Sunday: Thundery developments in evening, otherwise partly sunny day. Light showers in the evening in some areas. Rains about 5-7 mm/day.

Pune:
Friday: Thunder showers in the evening, lesser intensity, around 10 mms. 
Saturday/Sunday: Cloudy and warm day. Almost no rains.

Chennai City: 
Friday/Saturday: Chances of a thunder shower "popping up" in some parts of the city. Regional rains upto 7-10 mms.
Sunday: Partly cloudy and warm. 

Delhi NCR: Cloudy and stuffy weekend.
Friday: Sunny, getting cloudy later in the day.
Saturday/Sunday: Cloudy day, and stuffy nights. Day temperatures around 32c on Saturday, rising on Sunday.

Kolkata: Clearing after Friday.
Friday: Remaining moisture from BB-13 will bring thunder showers in many parts of the city during the day.
Saturday/Sunday: Rains and shower intensity and frequency decreasing on the weekend.

Hyderabad: Heavy thunder shower. Saturday/Sunday: Light rain in some parts of city on Saturday after cloudy day. Sunday will be without any meaningful rains.

From Vagaries

RT @archvivekh: Raining in Ambattur! #Chennai @weatherofindia (8:11pm)

RT @archvivekh: @weatherofindia heavy rains lashing the whole of Ambattur for past hour! Woo hoo$! (8:49pm)

#Chennai - 7:36pm, moderate mini showers seen over West from city at around 40 to 60km. May push into W,S-W,N-W suburbs of city.

6:30pm, The low.mid level N Bay circulation has moved inland, now over Jharkhand, Odisha and N,central Chatisgarh http://ow.ly/i/3bYEl 
7pm, Heavy rain over E Uttarpradesh, E Madhyapradesh, central,N Chatisgarh, N,N-E Andhra, S Odisha, W,S,central,E Maharastra and Jharkhand.

12pm, #Monsoon (Saaral) rains pummelling our ghats, Mahendragiri to Naraikadu ranges ... PHOTO ... http://ow.ly/i/3bSkU 

#kolkata, yesterday and today !

#Kolkata - 11:50am, "COLOSSAL RAINS HIT SOUTH KOLKATA" and now (1:12pm) it is Clearing !

PHOTO >> This was #Kolkata yesterday (taken from https://www.facebook.com/WeatherOfKolkata) ... http://ow.ly/i/3bRrH 

DUE TO THE LOW OVER N.BAY, LAST 24 HRS HAS BEEN WET WET WET FOR EAST INDIA 
SOME OF THE HEAVY RAINFALL OF EAST INDIA IN 24 HRS ending 8:30am Today.

1. CONTAI (WB) - 188.4 MMS
2. BARIPADA (OR) - 158.4 MMS
3. JAMSHEDPUR (R) - 61.4 MMS
4. DIGHA (WB) - 45.8 MMS
5. BALASORE (OR) - 42.3 MMS
6. PURI (OR) - 38.8 MMS
7. RANCHI (R) - 38.4 
8. BASHIRHAT (WB) - 29.4 MMS
9. MEDNIPUR (WB) - 24.2 MMS
10. BANKURA (WB)- 25.5 MMS
11. BHUBANESHWAR - 23.5 MMS
12. ALIPUR (KOL WB) - 20.8 MMS
13. JHRASGUDA (OR) - 19.8 MMS
14. DUMDUM (KOL WB) - 15.5 MMS
15. PATNA (BH)- 15.9 MMS

Update on N Bay LOW and its prospects

Today, the N Bay LOW persists ... http://ow.ly/i/3bOZv 

The low, mid level circulation associated with N Bay LOW can be seen along N Odisha coast ... http://ow.ly/i/3bP3s 

There's another low,mid level circulation seen over N Karnataka and N-W Andhra ... http://ow.ly/i/3bP3s

Upper level 500hpa circulation is seen along Odisha coast... this is expected to drift S-W upto N-E Andhra in 36hrs http://ow.ly/i/3bPQ6 

The upper level circulation after drifting upto N-E,central Andhra coast in 36hrs, it is expected to move N-W into Maharastra on 22/23-Sep

GFS and NAVGEM models expect the present N Bay low level circulation to move West upto Madhyapradesh on 23-Sep.. http://ow.ly/i/3bQ3l 

During next 24 to 48hrs, rain expected to persist over W,S central maharastra.
HEAVY rain due to N Bay LOW will slowly push into most of Odisha, Chatisgarh and into E,S-E Madhyapradesh, S,E Uttarpradesh on 20,21-Sep
Heavy Showers over S,central Bengal is expected to subside from tonight ! Isolated moderate rain will persist till tomorrow evening.
Scattered HEAVY rain also expected for entire coast of Andhra and for N,N-E Tamilnadu, #Chennai during next 2 days.
HEAVY rain along S Maharastra coast, Goa, Karnataka coast and Kerala to continue for next 36hrs.. expected to reduce from Saturday !
Scattered Moderate rain expected for S Karnataka, #Bangalore and S Andhra during next 3 days !
During next 48hrs, scattered Rain expected over N,N-E Andhra... this depends on the upper level circulation's drift into N-E Andhra coast.
HEAVY rain to continue over Kerala and Karnataka coast during next 2 days !

#Chennai late evening T shower, 18-Sep

Chennai - 9:43pm, heavy rain just started over Polichalur.

gsankar2011Sep 18, 9:46pm via Twitter for Android

@weatherofindia Wah. It's raining in Chennai. Haven't had such accurate prediction of rain. Good job.

archvivekhSep 18, 9:46pm via Twitter for BlackBerry®

@weatherofindia pouring in Ambattur! Wow! Loving it

_M0HIT_Sep 18, 9:49pm via Twitter for Android

@weatherofindia loving this...rain here always pleases me :-)

vipinkumar_gSep 18, 10:04pm via Twitter for BlackBerry®

@weatherofindia heavy rain near cenotaph road. Chennai - 10 pm

vipinkumar_gSep 18, 10:08pm via Twitter for BlackBerry®

@weatherofindia Traffic Congestion in Mount road due to heavy rain.

arjuunsramanSep 18, 10:10pm via Twitter for Android

It's pouring crazy in Chennai western suburbs - Mugalivakkam, Porur for the last half an hour!! @weatherofindia

fabwriteSep 18, 10:22pm via Twitter for iPhone

It's raining cats & dogs in #Mandaveli#Chennai @chennaiweather@weatherofindia

Arvind_LFCSep 18, 10:23pm via Web

@weatherofindia Heavy rain with massive thunder n ligthning in vadapalani!!#chennairain

#Chennai Rain alert, 9pm

@mihirkparekh >> #Goa, karnataka coast, S coast Maharastra - can get more heavy and V.Heavy rain on Thursday, Firday and even into Saturday.

#Chennai - 9pm, A heavy T Shower system is nearing city from W-N-W. This system may cover entire Chennai city. May reach in 30 to 40 min !

Heavy rain over #Kolkata, 6pm

RT @bumblme: raining cats and dogs for almost an hour now... #Hyderabad #rains 5:51 PM @weatherofindia 

#Kolkata - 6:04pm, very heavy rains lashing .
130 mms/hr rainfall going on ....
strong thunderstorm


#Chennai - 6:45pm, Showers continue over Ponneri zone even now. Showers expected to push into city before 9/10pm.

Update on N Bay and N.Karnataka circulations !

#Chennai - 4:15pm, #HOT at 35 C (feels like 39 C). And showers seen over Ponneri zone North from city at around 30km.

4:30pm, HEAVY rain over Bengal, Jharkhand, Odisha, N Chatisgarh, N,N-E Andhra, S Maharastra due to circulations... http://ow.ly/i/3bjzx 

Bangalore - 4:03pm, "quick rain at domlur zone"

Belgaum - 5:30pm, "Its over cast condition from yesterday with intermittent drizzling.Yesterday night got a heavy rain for one hour."

Today, there was 2 circulations, one over N Bay along Bengal and another over S-central Maharastra ... http://ow.ly/i/3bjZU 

Today, the low level Anti-cyclone persists over N-W,N-central India ... http://ow.ly/i/3bjZU

The N-central Anti-cyclone and the weakened monsoon axis will not allow the N-W movement of Bay circulation.

The N Bay circulation may drift S-W along coast upto N-E Andhra coast in next 2 days.

Today, there's an upper level circulation seen over N Karnataka and N-W Andhra, Hyderabad ... http://ow.ly/i/3bkc4 
The N Karnataka circulation is also expected to persist in almost same zone for next 2 days.

Kolkata - 5:36pm, "Its raining here."