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New Delhi, April 15, 2020
The India Meteorological Department (IMD) today said the 2020 southwest monsoon seasonal (June to September) rainfall over the country as a whole was likely to be normal (96-104%).
In its Long Range Forecast for the 2020 Southwest Monsoon Season Rainfall, the IMD said that, quantitatively, the monsoon seaonsal rainfall is likely to be 100% of the Long Period Average (LPA) with a model error of +/- 5%.
The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.
A press release from IMD said neutral El Nino Southern Oscillation (ENSO) conditions are prevailing over thePacific Ocean and Neutral Indian Ocean Dipole (IOD) conditions are prevailing over the Indian Ocean. Some climate model forecasts indicate these conditions are likely to persist during the ensuing monsoon season. However, a few other global climate models indicate possibility of development of weak La Nina conditions over the Pacific Ocean during the second half of the season.
As sea surface temperature (SST) conditions over the Pacific and Indian Oceans are known to have strong influence on Indian monsoon, IMD is carefully monitoring the evolution of sea surface conditions over the Pacific and the Indian oceans, it said.
IMD said it would issue the updated forecasts in the last week of May or the first week of June 2020 as a part of the second stage forecast. Along with the updated forecast, separate forecasts for the monthly (July and August) rainfall over the country as a whole and seasonal (June-September) rainfall over the four broad geographical regions of India will also be issued.
IMD issues operational forecast for the southwest monsoon season (June to September) rainfall for the country as a whole in two stages. The first stage forecast is issued in April and the second stage forecast is issued in May/June.
These forecasts are prepared using the state-of-the-art Statistical Ensemble Forecasting System (SEFS) that is critically reviewed and improved regularly through in-house research activities. Since 2012, IMD is also using the dynamical global climate forecasting system (CFS) model developed under the Monsoon Mission to generate experimental forecasts. For this purpose, the latest version of the Monsoon Mission CFS (MMCFS) model was implemented in January 2017 at the Office of Climate Research and Services, IMD, Pune.
IMD’s SEFS model for the April forecast uses the following 5 predictors that require data upto March: The Sea Surface Temperature (SST) Gradient between North Atlantic and North Pacific (December and January); Equatorial South Indian Ocean SST (February); East Asia Mean Sea Level Pressure (February + March); Northwest Europe Land Surface Air Temperature (January) and Equatorial Pacific Warm Water Volume (February + March).
The release said that, for the forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS), rainfall atmospheric and oceanic initial conditions during March 2020 were used. The forecast was computed as the average of 51 ensemble members.
According to it, the forecast based on the MMCFS suggests that there is a high probability (70%) for the 2020 monsoon rainfall to be above normal to excess (more than 104% of LPA).
In the forecast based on the Operational Statistical Ensemble Forecasting System, the IMD said that, quantitatively, the monsoon seasonal rainfall is likely to be 100% of the LPA with a model error of +/- 5%.
The statistical model for the 5 category probability forecasts for the Seasonal (June to September) rainfall suggests a high probability (41%) for 2020 monsoon rainfall to be normal (96-104% of LPA), the release said.