The southwest monsoon will be normal in the range of 96-104 per cent across the country, said the India Meteorological Department (IMD) as part of its Long Range Forecast (LRF) for the rainy season from June to September 2021.
According to IMD, the monsoon rainfall will be 98 per cent of the Long Period Average (LPA), which could differ by 5 per cent plus or minus of the quantitative forecast. The LPA for the monsoon rainfall for the period 1961-2010 is 88 cm in the country.
Rainfall in Odisha, Jharkhand, eastern Uttar Pradesh, Assam and Meghalaya is likely to be below normal, but normal or above normal in the rest of the country, he said while releasing the first Long Range Forecast for the four-month rainfall period from June to September.
According to the prediction of the Operational Statistical Ensemble Forecasting System (SEFS), there is a 40 per cent probability of a normal and 16 per cent probability of an above normal rainfall this season. There is a 25 per cent probability of a below normal rainfall, the IMD said.
This is the first time the IMD has made a specific forecast on spatial distribution.
The Pune-based IMD has been also using a high-resolution dynamical global Climate Forecasting System (CFS), which was developed under the Monsoon Mission of the Ministry of Earth Sciences (MoES).
The IMD has now developed a Multi-Model Ensemble (MME) forecasting system based on coupled global climate models (CGCMs) from different global climate prediction and research centers, including the Monsoon Mission CFS (MMCFS) being used by the IMD.
Meteorologists consider certain parameters while making a monsoon forecast. Among them are La Niña conditions (colder than normal sea surface temperature — SST over the equatorial Pacific), which developed during second part of the previous year and peaked in November. La Niña conditions indicate a good monsoon as against El Niño conditions, which are associated with drought or weak monsoon.
However, La Nina conditions over the equatorial Pacific started weakening in the early part of 2021 and these conditions are now moving towards El Niño/Southern Oscillation (ENSO) neutral conditions. Subsurface temperatures over the equatorial Pacific have substantially warmed and atmospheric patterns reflect neutral ENSO conditions. The latest Monsoon Mission Climate Forecasting System (MMCFS) and other global model forecast indicate further warming trends and retuning of ENSO neutral conditions in the early part of the upcoming monsoon season.