Even as tell-tale signs of a weakened monsoon become apparent, the India Meteorological Department (IMD) has said that rainfall activity would increase over the West Coast over the next five days (from June 18).
Fairly widespread to widespread rainfall is being forecast over the islands — Lakshadweep in the Arabian Sea and Andaman & Nicobar in the Bay of Bengal — in what are signals of a gradual and broad improvement in monsoon flows.
MJO wave expected
What goes to further enhance this probability is the expected arrival of the next ‘wet phase’ of the Madden-Julian Oscillation (MJO) wave from West Africa during the next week.
The wave is seen taking the whole of next week to reach the Indian Ocean (with implications for the Arabian Sea and the Bay, in that order) and be of relevance to the ongoing monsoon.
An ensemble model of the US National Centres for Environmental Prediction suggests that a favourable ‘buzz’ would develop in the North Bay between June 25 and 29, likely precipitating a low-pressure area.
This ‘low’ would be crucial with respect to driving the monsoon further into Central India, which is normally covered by June 15, and contiguous North-West India.
It was a predecessor MJO wave that set up the two cyclones in the Arabian Sea and later the onset of the monsoon over Kerala, in what is a known pattern with the wave that travels periodically from the West to the East over the Indian Ocean.
Meanwhile, the IMD has forecast isolated to scattered rainfall for the South Peninsula, Central India, the northern plains and the western Himalayan region from June 18.
The rainfall predicted for North-West and Central India as well as the western Himalayan region would be the result of activity triggered by the pre-monsoon trough. For the monsoon to set in over these regions, the monsoon easterlies originating from the Bay have to establish and fan into the trough. This is not seen happening before June 20-22. Formation of a ‘low’ in the Head Bay alone can do this.
Non-seasonal troughs
On Wednesday, the presence of non-seasonal troughs over land at a few places indicated what is not right with the monsoon currently. These features show up only during its weak phase.
One such trough ran down from South Odisha to North Coastal Karnataka across South Chhattisgarh, Telangana and North Interior Karnataka. It can cause lightning and thunderstorms to form.
Another trough runs from Nagaland across Assam and Meghalaya linking the hills of Bengal. Last but not the least, a western disturbance was present over Jammu & Kashmir from Tuesday, but had moved out a day after.