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IMD forecasts normal monsoon this year

Vinson Kurian Thiruvananthapuram | Updated on April 17, 2021

Likely to be 98 per cent long-period average

India is likely to have a normal monsoon this year (assessed at 98 per cent of long-period average LPA), which is on a trend that aligns with two consecutive years of above normal monsoon in 2019 and 2020, according to the monsoon long-range forecast issued by India Meteorological Department (IMD) on Friday.

The forecast based on operational Statistical Ensemble Forecasting System (SEFS) suggests that quantitatively, the monsoon seasonal rainfall is likely to be 98 per cent of the LPA with a model error of ± 5 per cent per cent.  The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.

 

Spatial spread of rainfall

The five-category probability forecasts for the seasonal (June to September) rainfall over the country as a whole based on the SEFS forecast suggests maximum probability for the seasonal rainfall to be normal (which is defined as 96-104 per cent of LPA).

The spatial distribution of probabilistic forecasts for tercile categories (above normal, normal and below normal) for the seasonal rainfall suggests either normal or above normal probability is likely over most parts of the country, M Rajeevan, Secretary, Ministry of Earth Sciences, told a virtual press conference on Friday. 

As for the spread of rainfall, he indicated that the eastern parts of the country may alone witness drier than usual conditions and deficient rain during the impending season.

La Nina phase easing

The La Nina phase in the Equatorial Pacific Ocean, among the major climatological factors deciding the monsoon play-out, is easing and is very near to the threshold in terms of prevailing sea-surface temperatures (SSTs).

The La Nina phase (cool SSTs in the tropical Central and East Pacific as against warmer waters in the West Pacific) tends to support a good monsoon, as was the case in the last year. But, according to Rajeevan, model predictions support a transition to the ‘neutral’ phase (neither La Nina/El Nino) by May.

Indian Ocean Dipole

The Indian Ocean Dipole (IOD), twin of the Pacific phenomenon closer home, is also assessed to be in the neutral phase, Rajeevan said, with a tendency to go to the negative mode during the monsoon.

The forecast by the national forecaster for a normal monsoon is follows a ‘healthy normal monsoon’ outlook made available on Tuesday by Skymet Weather, a leading private sector forecaster, and assessed at 103 per cent of the LPA.

The forecast of a good monsoon for the third consecutive year should bring good tidings for the farm economy even as the Covid-19 pandemic in most parts of the country.

 

Table: The five-category probability forecasts for the monsoon rainfall over the country as a whole suggests maximum probability for monsoon seasonal rainfall to be normal (96-104 per cent of LPA).(Source: IMD)

 

Published on April 16, 2021

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