Posted 20th May Morning:

Rainy week ahead for most of the west coast and peninsular India...SW Monsoon on the horizon☔

As mentioned in our earlier post, the upper air cyclonic circulation (UAC) has moved over peninsular India from the Bay of Bengal. It is about to emerge over the Arabian Sea and a surface low pressure area is likely to form around 22nd May off the Karnataka/Goa coast. 

This low may intensify as it tracks north-northwest...there is a possibility of it intensifying into a deep depression or a cyclone...needs to be monitored. 

Today morning's wind pattern shows Southwest Monsoon established till Sri Lanka...with a cyclonic circulation over Karnataka coast.

The southwest winds are expected to strengthen over the Arabian Sea in the coming days, with the Monsoon likely hitting the Kerala coast around 24th May (+/- 2 days), which is around a week ahead of schedule. 

Thereafter, under the influence of the strengthening low (which may have become an onset vortex/depression by then), the monsoon can quickly advance over the west coast and possibly reach Goa around 27th/28th May. 

Further progress of the monsoon along the west coast and in the interior peninsula depends upon the track of the Arabian Sea system. 

As the scenario is unfolding, (and if persisting), Mumbai can herald in the Monsoon around 1st June (+/- 2 days). Interior South Maharashtra around 1st June and North Madhya Maharashtra 3rd June 

At present, model forecasts also indicate a chance of a low pressure system forming over the northern Bay of Bengal by early next week and tracking westwards, which could help advance the Monsoon over eastern states.

More updates on this in subsequent posts.

This May has been quite cooler and wetter than normal (below images from IMD)

Decoding how the weather has evolved since the start of this month👇

⇨ We had an unusually strong and southward dipping Western Disturbance (WD) in the first week of May. 

⇨ This ensured that the seasonal high pressure system over the Arabian Sea is disrupted. 

⇨ After this strong and prolonged WD lasting for a few days, the line of wind discontinuity formed over the peninsular India and Western Ghats, which resulted in fairly regular thunderstorms in these regions stretching from Maharashtra into Kerala/Tamil Nadu, across Karnataka, Telangana and Andhra Pradesh.

⇨ A UAC formed over the Bay of Bengal by the end of the second week of May, and has tracked westwards, bringing in moisture over the peninsular India from both the east as well as west (pull-effect). This UAC is now seen merging with the east-west shear zone, which is associated with the northward advance of the monsoon.
 
⇨ The seasonal high pressure over the central Arabian Sea did not get established. On the other hand, the cross-equatorial flow from the Indian Ocean in the southern hemisphere has strengthened. 

⇨ Overall, the seasonal northward-moving Monsoonal circulation is seen strengthening across the Indo-Pacific regions. 

⇨ As a result, the Southwest Monsoon is running ahead of schedule by around a week, with an earlier onset seen over the Andaman & Nicobar region and an earlier onset expected over Kerala.