The TrickyScribe: India is likely to get what the experts describe as “normal” monsoon rains for the third straight year in 2018. India Meteorological Department (IMD) has predicted that the country will receive 97 percent of the long-period average rainfall, with skimpy chances of a deficient monsoon. Error margin of 5 percent is predicted for 2018.
Such forecast is the first set of good news but for agriculture, spatial and temporal distribution of monsoon is as critical. Private weather forecast agencies including Skymet had earlier predicted monsoon rains in India at 100 percent between June and September.
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It may be mentioned here that the IMD issues operational forecasts for the southwest monsoon seasonal (June to September) rainfall for the country as a whole in two stages. The first stage forecast being issued in April, while the second stage forecast in June.
Prepared using Statistical Ensemble Forecasting system (SEFS), these forecasts are critically reviewed and improved time and again. Dynamical global climate forecasting system (CFS) model developed under the Monsoon Mission was put into forecast generation in 2012.
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IMD’s SEFS model for the April forecast uses five predictors that require data up to March. The predictors include Sea Surface Temperature (SST) Gradient between North Atlantic and North Pacific, Equatorial South Indian Ocean SST, East Asia Mean Sea Level Pressure, Northwest Europe Land Surface Air Temperature and Equatorial Pacific Warm Water Volume.
Forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS)
Forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS) for the 2018 Southwest Monsoon Season (June-September) rainfall over the country as a whole is likely to be 99 percent with a tolerance of 5 percent of the LPA.
Forecast Based on the Operational Statistical Ensemble Forecasting System (SEFS)
Monsoon seasonal rainfall is likely to be 97 percent of the Long Period Average (LPA) with a model error of 5 percent. Five-category probability forecasts for the Seasonal (June to September) rainfall over the country suggest maximum probability for normal rainfall and a low probability of deficient rainfall during the season.
Sea Surface Temperature (SST) Conditions in the equatorial Pacific & Indian Oceans
Moderate La Nina conditions developed in the equatorial Pacific during last year started weakening in the first quarter and currently have turned weak. The latest forecasts from MMCFS and other global models indicate conditions over the Pacific to turn to neutral ENSO conditions before the onset of monsoon season. Neutral Indian Ocean Dipole (IOD) conditions were prevailing over the Indian Ocean while going to press.
Latest forecasts indicate weak negative IOD conditions for the mid-monsoon season. Extreme sea surface temperature conditions over the Pacific and Indian Oceans particularly ENSO conditions over the Pacific (El Nino or La Nina) are known to have a strong influence on the Indian summer monsoon, sea surface conditions over the Pacific and Indian oceans are being closely monitored.