IMD forecast had said monsoon was "mostly likely" to be normal
The much-awaited southwest monsoon could finally be on its way. The India Meteorological Department on Tuesday predicted that the monsoon is likely to set in over Kerala on June 1, with a model error of plus or minus four days.
[June 1 is the normal date for the onset of the system over Kerala, which is the entry point for the monsoon into the Indian mainland. Historical data show that the monsoon by and large keeps its date with a standard deviation of just one week. There have, however, been instances when the onset had occurred around the middle of May itself, or had got postponed to mid-June.
According to senior meteorologists at IMD, the earliest recorded onset was in 1918, when it set in on May 11, and the most delayed onset was in 1972, when people had to wait with bated breath till June 19].
The prediction of a normal onset comes on the heels of a forecast issued by IMD on April 26, that the southwest monsoon this year was “mostly likely” to be normal, with a rainfall of 99 per cent of the long period average [LPA], with a model error of plus or minus 5 per cent.
That forecast also noted that there was a 47 per cent probability of the rainfall being between 96 per cent and 104 per cent, 24 per cent probability for it to be between 90-96 per cent, 17 per cent probability for it to be between 104-110 per cent, eight per cent probability for it being below 90 per cent, and four per cent probability for it being above 110 per cent of the LPA.
In other words, rainfall was likely to be between 94 per cent and 104 per cent of the LPA, with a greater possibility for it to be near the lower end of the band than the upper end.
It remains to be seen if the onset would really take place around the normal date, as there are still 15 days to go, and anything could happen in the meantime. As of now, there are bright prospects, as there are indications that the monsoon flow is strengthening, and that it can appear over the Andaman Sea within the next few days, before moving on to Kerala.
It also remains to be seen how the monsoon season actually unfolds, even if the onset of the monsoon over Kerala happens around the normal date as there is no one-to-one association between the date on onset over Kerala and the temporal and spatial spread of the seasonal rainfall over different parts of the country.