All available indications point to a strong phase of South-West monsoon in the first week of June, after seasonal rains break over Kerala coast. This would be underwritten by a wet phase of Madden-Julian Oscillation (MJO) wave that passes above the Indian Ocean during this period.
MJO INFLUENCE
Though travelling high up, the wave is able to influence ground weather by facilitating formation of clouds, precipitating rains, even triggering storms and monsoon onset. The Climate Prediction Centre of the US National Weather Services has said that the Indian Ocean, South India and Sri Lanka are expected to get impacted.
AUTO-PILOT MODE
The strong phase would kick off from May 28 and last for 11 days until June 7. Gusty winds might bear down over Kerala and Konkan-Mumbai coasts and trigger copious rain. Rains may relent later, depending on how monsoon dynamics become established by that time.
Normally, a strong phase helps monsoon shift to auto-pilot, which means that the strength of the flows would be enough to carry it along with or without an MJO wave.
Available indications suggest that this could indeed be the situation, and the monsoon is shown as running up whole peninsula and East India thanks to concurrent activity in the Bay of Bengal. US forecast models have also indicated thatJune could likely witness normal to above normal rainfall.
Meanwhile, India Met Department said on Thursday that rainfall could scale up along the West Coast and Lakshadweep from Sunday.
This would set the stage for copybook-style conditions culminating likely in onset of the monsoon early next week, according to international weather models
THUNDERSHOWERS
A prominent pre-monsoon atmospheric formation is already setting up a chain of thunderstorms over peninsular and South India.
The weather-setting trough of lower pressure runs from South Jharkhand to South Tamil Nadu across South Chhattisgarh and interior Andhra Pradesh.
The trough receives moisture from the seas on either side, which combines with the hot air to set up clouds and thundershowers along the line. Thundershowers are forecast to break out over Kerala, Karnataka, Lakshadweep, South Konkan, Goa, South Madhya Maharashtra, Andhra Pradesh and Tamil Nadu until Sunday.