New Delhi: The India Meteorological Department (IMD) has forecast that the impending southwest monsoon season is likely to be ‘near normal’, with a rainfall of 96% of the long-term average with a model error of 5%, give or take.
M. Rajeevan, the secretary of the ministry of Earth sciences, announced the forecast and said the rain was expected to be well-distributed. The season begins in June and ends in September.
He noted that there was a weak El Niño condition and that it was likely to prevail through the season, though the intensity could reduce from July onwards.
“The sea surface anomaly over equatorial the Pacific Ocean region, which is responsible for the El Niño, is at present between 0.5º C and 1º C. This could have some impact at the beginning of the season. But it would gradually reduce as the season progresses. The existence of a weak El Niño condition has been accounted for in the forecast,” he said.
The IMD issues its operational forecast for the southwest monsoon season in two stages. The second forecast will be issued in June, when more information on various parameters that affect the monsoon will become available.
The forecasts are prepared using statistical ensemble forecasting system and a dynamical coupled ocean-atmosphere global climate forecasting system, both developed under the ministry’s ‘Monsoon Mission’.
The statistical system uses five predictors for the first stage forecast: sea surface temperature gradient between the north Atlantic and the north Pacific from December to January; the equatorial south Indian Ocean sea surface temperature in February; the east Asian mean sea level pressure during February-March; the northwest Europe land surface air temperature during January; and the equatorial Pacific warm-water volume in February-March.
The dynamic model used global atmospheric and oceanic initial conditions up to March for the first stage forecast.
While the statistical model predicted a rainfall of 91-101% of the long-term average, the dynamic model predicted a little lower, at 89-99%. “Our final prediction is based on the findings of the models plus our own experience and knowledge acquired over the years,” said K.J.Ramesh, director general of the IMD.
Rajeevan said that the IMD would keep constant vigil over the El Niño southern oscillation so that corrective measures can be taken if required. In addition, scientists will also keep an eye on the Indian Ocean dipole [IOD], which influences the Indian monsoons.
“At present, neutral IOD conditions are prevailing and there are indications that it could become positive in due course and thus help the monsoon over India. We will keep a watch,” he added.
The IMD is expected to publish region- and month-wise forecasts while updating the seasonal and country-wide forecast in the second stage forecast, scheduled for June. Rajeevan clarified that forecast information of the rains’ onset would be available in the middle of May.