India’s South West Monsoon for 2021 is expected to be normal at 98 percent of the long-period average, the India Meteorological Department said on April 16.
A range of 96-104 percent of long-period average is considered as normal monsoon.
This will be the first normal monsoon in three years after two above-average monsoon rainfall in the last two years, which is welcome news for an economy dented by a second ‘wave’ of Covid-19 cases and reduced activity due to localized curfews and lockdowns.
“Southwest monsoon seasonal (June to September) rainfall over the country as a whole is most likely to be normal. Quantitatively, the monsoon seasonal rainfall is likely to be 98 per cent of the Long Period Average (LPA) with a model error of ± 5 per cent,” said Madhavan Rajeevan, Secretary of Ministry of Earth Sciences, at a media briefing.
By definition, the LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.
Looking ahead, Rajeevan said that the Met Department will issue monsoon forecasts in May for the whole period, and also monthly forecasts for June to September.
“Southwest monsoon seasonal rainfall over the country IMD will issue the updated forecasts in the last week of May 2021. In addition to update for the April forecast, forecasts for June to September rainfall for four homogenous regions and forecast for the month of June also will be issued,”he said.
Rajeevan said that for generating monthly forecasts, the met department will now use a dynamical multi-model ensemble (MME) framework instead of present statistical models.
“Monthly probabilistic forecast for all four months (June to September) will be prepared during the last week of previous month using the MME forecasting system,” he said, adding that the IMD has also been making efforts to develop a separate forecast for the Monsoon Core Zone (MCZ), which represents most of the rainfed agriculture region in the country.
“A separate forecast for the MCZ will be more useful for agricultural planning and crop yield estimation etc. In the second stage forecast in May, IMD will issue a separate probabilistic forecast for the MCZ, based on MME system and a new statistical model.”

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