The countdown for the four-month south-west monsoon season has begun.
The India Meteorological Department has forecast that the system is likely to set in over Kerala on May 31, with a model error of plus or minus four days.
Kerala is the first point of entry for the system in the Indian mainland. June 1 is the normal date for the onset over Kerala.
Meanwhile, monsoon flow, the IMD said, was expected to appear over the Andaman Sea in a few days and was likely to cover that region close to its normal date of May 20.
Close predictions
IMD has been issuing forecast for the onset for the past six years and the predictions have by and large come true. Last year, the Department said the onset could be on May 30, and the actual event occurred on May 31.
The Department has already forecast that rainfall during the season was “most likely” to be normal this year, at about 98 per cent of the long period average (LPA), with a model error of plus or minus five per cent.
In a note issued along with the forecast made on April 19, the IMD said the models showed there was a 53 per cent probability that the rainfall will be between 96 per cent and 104 per cent of LPA (normal), a 10 per cent probability that it will be between 104 per cent and 110 per cent of LPA (above normal), and one per cent probability that it will be above 110 per cent of LPA (excess).
On the downside, there was a 30 per cent probability of it being between 90 per cent and 96 per cent of LPA [below normal] and a six per cent probability of being below 90 per cent of LPA [deficient].
Update in June
The forecast is, however, not final. IMD will update it in June after taking into account parameters for which data would be available only by then. This is an annual routine.
Among other things, the majority of international models monitoring El Nino-La Nina have indicated that sea surface temperatures over equatorial Pacific are getting warmer. Consequently La Nina conditions, which could otherwise have been beneficial for monsoon, are weakening and are expected to reach ENSO condition by June. But, long term forecasts for El Nino-La Nina are fraught with large uncertainties. The El Nino-La Nina phenomena may unfold in a different way from the present forecast.
IMD director general Ajit Tyagi said the department would be keeping a close watch on the phenomena to ensure that the country was well prepared in case of any major changes.
Indian Ocean Dipole
The IMD, he said, would also closely monitor the developments relating to Indian Ocean Dipole, which relates to anomalies in the sea surface temperatures between eastern and western parts of the Indian Ocean.
At present, international models are forecasting that a negative IOD could develop and that it could happen in the last part of the monsoon. Consequently, as of now, there does not seem to be any possibility of a major impact.
It, however, remains to be seen how it actually develops. If it were to develop earlier, there could be a negative impact on the quantum of rainfall.
