New Delhi, Apr 15: The seasonal rainfall during the Southwest Monsoon (June to September) over the country as a whole this year is most likely to be above normal, at over 104 per cent of the Long Period Average (LPA), the India Meteorological Department (IMD) announced on Tuesday.

Quantitatively, the seasonal rainfall over the country as a whole, based on both dynamical and statistical models, is likely to be 105 per cent of LPA, with a model error of plus/minus 5 per cent, the IMD said, as per an Earth Sciences Ministry statement. The LPA of the seasonal rainfall over the country as a whole for the period 1971-2020 is 87 cm.

As per the IMD, neutral El Nino-Southern Oscillation (ENSO) conditions are prevailing over the equatorial Pacific region, but the atmospheric circulation features are similar to La Nina conditions. The latest Monsoon Mission Climate Forecast System (MMCFS) as well as other climate model forecasts indicate that the Neutral ENSO conditions are likely to continue during the monsoon season, it added.

The weather agency also said that present, neutral Indian Ocean Dipole (IOD) conditions are present over the Indian Ocean and the latest climate models forecast indicates that these are likely to continue during the Southwest Monsoon season.

It also noted that the snow cover areas of the northern hemisphere and Eurasia during the last three months (January to March 2025), which generally have an inverse relation with the Indian summer monsoon rainfall, were below normal.

The IMD's five-category probability forecasts for the seasonal (June to September) rainfall over the country as a whole suggest that there is a strong probability (59 per cent) of Southwest Monsoon seasonal rainfall likely to be in the above normal category or higher (excess), that is greater than 104 per cent of the LPA.

The forecast probability for a normal monsoon is 30 per cent, of a below normal monsoon is 9 cent, and of a deficient monsoon is 2 per cent.

The IMD said it will issue the updated forecasts for monsoon season rainfall in the last week of May, as per the practice since 2003.

Since then, the IMD issues the operational long-range forecast (LRF) for the southwest monsoon seasonal (June-September) rainfall averaged over the country as a whole in two stages - first in April and the second at the end of May.

In 2021, the IMD implemented a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall over the country by modifying the existing two-stage forecasting strategy. The new strategy uses both dynamical and statistical forecasting systems. The Multi-Model Ensemble (MME) forecasting system is based on coupled global climate models (CGCMs) from different global climate prediction centres, including IMD’s Monsoon Mission Climate Forecast System (MMCFS).

As per the new LRF strategy, the first stage forecast issued in middle of April consists of the quantitative and probabilistic forecasts for the country as a whole, and the spatial distribution of probabilistic forecasts for the tercile categories (above normal, normal, and below normal) of the seasonal (June-September) rainfall over the country.

The second stage forecast issued around the end of May consists of an update for the seasonal rainfall forecast issued in April, along with the probabilistic forecasts for the seasonal rainfall over the four homogenous regions of India (northwest India, central India, south Peninsula and northeast India) and monsoon core zone (MCZ). In addition, quantitative and probabilistic forecasts for the country as a whole, and the spatial distribution of probabilistic forecasts for the tercile categories (above normal, normal, and below normal) of the June rainfall over the country are also issued during the second state forecast.

In continuation of the above forecasts, monthly rainfall forecast is issued around the end of June, July, and August, respectively, for the subsequent month. In addition, quantitative and probabilistic forecasts for the country as a whole, and the spatial distribution of probabilistic forecasts for the tercile categories for the second half of the season rainfall is issued around end of July along with the forecast for August.

--IANS

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