Kerala and Coastal Karnataka are the rainiest pockets of the country during the monsoon season. Northeast India and the Western Ghats are the chief contributors to the Indian Summer Monsoon Rainfall (ISMR). Large deficiencies in any one of these two regions drag the monsoon status below parts. In the early days of monsoon, as of now, the northeastern region is having mixed response. Assam-Meghalaya and Sikkim have excess rainfall and Arunachal Pradesh, along with Nagaland, Manipur, Mizoram, and Tripura have a deficiency of about 30% rainfall. Along the West Coast, all three subdivisions, namely, Konkan & Goa, Coastal Karnataka, and Kerala have a deficiency of seasonal rainfall.
Lull in the monsoon activity along the Western Ghats is attributed to the lack of monsoon systems in the Bay of Bengal. Not a single system has formed so far in the Indian seas, on either side of the coastline. The build-up of monsoon systems accentuates the monsoon stream over the Arabian Sea and there on to the West Coast. Conditions are becoming favourable to activate the streaming of westerly winds along the Ghats and the intensification of rainfall activity.
There is an in-situ cyclonic circulation forming over Odisha, Jharkhand and Chhattisgarh. This will move westward over the central parts and drag the westerly winds from the Arabian Sea, heading onto the coastline of Kerala and Karnataka. There is another supporting feature coming up over the Bay of Bengal, albeit a little far, along the coastline of Myanmar, around the Gulf of Martaban. A cyclonic circulation is coming up over that area and will move along Myanmar's coast. This is not likely to enter the open waters of the Bay of Bengal. However, the presence and movement of this feature will strengthen the monsoon current along the West Coast.
Under the influence of these two systems, monsoon activity will increase all along Kerala and Coastal Karnataka. Heavy to very heavy rainfall is likely over these two sub-divisions, commencing 22nd June. The intensity and spread will be large between 22nd and 24th June. Moderate rainfall with heavy showers at a few places will continue on the 25th and 26th over these two regions. Rainfall will become light for Kerala from the 27th onward. However, the weather activity will continue over Coastal Karnataka for 2 more days, till 28th June. Heavy rainfall belt will extend to the Konkan region also, during this period. Most places along the Konkan Coast, including Mumbai, will have moderate to heavy rainfall between the 24th and 28th of June. Mumbai needs to exercise caution for heavy rains between 26th and 28th June.
