The South-West monsoon could arrive over the Kerala coast by May 25, according to PV Joseph, renowned monsoon researcher and a former director of India Met Department.
But the early onset does not have any correlation with the ultimate performance of the four-month-long season that extends from June 1 to September 30.
El Nino effect
In fact, a majority of the ocean-atmosphere coupled models have predicted that El Nino conditions are likely to set in during the second half of the monsoon.
"We had a negative Indian Ocean Dipole during September to November last year. Such a condition is generally followed by an El Nino in the next year.
"With an El Nino around,we may expect less than normal all-India rainfall this year."
Joseph, who is often consulted by the Met Department, based his assessment of the likely onset timeline on the observed 'pre-monsoon rain peak' phenomenon this year.
The 'pre-monsoon rain peak' is represented by a band of raining cloud extending from Kerala eastwards into the Bay of Bengal.
Early monsoon buzz
Joseph's pioneering work on the phenomenon is among the key parameters considered by the Met Department for its forecasts.
He told BusinessLine that the 'pre-monsoon rain peak' can form any time between the first week of April and the second week of May. Its timing gives prior indication of the date of monsoon onset over Kerala.
For a normal monsoon onset that occurs on June 1, the raining band of cloud in the Bay of Bengal should form around April 21.
"This year, however, it was seen in satellite pictures and low-level wind charts during the last two to three days indicating that the monsoon onset over Kerala is likely to be early by about a week, say by May 25," he explained.
In many years in the past, the raining cloud band and the westerly winds associated with it has caused the genesis of a depression or a cyclonic storm in the Bay of Bengal, just to its north.
Cyclone, heat waves
In addition, the surface temperature of Bay of Bengal is warmer than normal by about one degree Celsius this year.
"We may expect the formation of a cyclonic storm in the Bay during April 15 to 20. But soon after that the raining clouds are likely to shift to the western Pacific ocean."
During the period from May 1 to 10, India is likely to face largely dry conditions with decreased rainfall and occurrence of heat waves.
From around May 10, a band of raining clouds is likely to form over the South Arabian Sea, which will increase in area covered and intensity to bring about the monsoon onset over Kerala around May 25, accompanied by strong low level winds and heavy and persistent rainfall.
This description is based on the climatology (average) of the monsoon onset process that takes place over the Indian Ccean during the 40-day period after the pre-moonsoon rainfall peak, Joseph said.