The India Meteorological Department (IMD) recently projected that India is likely to experience a normal monsoon, potentially exhibiting increased rainfall in August and September, 2020. This is expected to significantly influence the country’s climatic conditions this year.
Annual Two-Stage Forecast System
Annually, the IMD releases two forecasts. The first forecast is issued in April, followed by a more comprehensive one in the last week of May. The latter provides detailed insights into how the monsoon will spread across the country in different regions.
Forecast for June-September Rainfall
The rainfall ranging from June to September contributes to about 75% of the country’s annual rainfall. The monsoon seasonal rainfall is estimated to be approximately 100% of the Long Period Average (LPA) with an error margin of ± 5%. The LPA of the season’s rainfall across India for the period 1961-2010 was determined as 88 cm. The IMD recently revised the definition of ‘normal’ rainfall, reducing it by 1 cm to 88 cms.
Influence of Indian Ocean Dipole
The Indian Ocean Dipole, a temperature discrepancy in the ocean that can enhance monsoon rain, is also predicted to maintain a “neutral” state throughout the monsoon. This phenomenon, as suggested by the statistical model, gives a 41% forecast probability of a normal monsoon.
Expectation of Excess Rain
The prospect of surplus rain is derived from a forecast by the dynamical model. This model proposes that there is a high likelihood (70%) of above-normal to excessive rainfall than usual.
Comparison with 2019’s Forecast
In April 2019, the IMD stated that the monsoon would be near or slightly below normal. However, due to torrential rain in August and September resulted from unusual warming in the Indian Ocean, India experienced the highest rainfall in a quarter-century.
Monsoon Forecasting Models
The IMD uses two primary models to forecast the monsoon: The Dynamical Model, also known as the Monsoon Mission Coupled Forecast System, and the Statistical Model. The Dynamical Model is more proficient at predicting weather conditions a week or two in advance. However, meteorologists do not consider it reliable for forecasting the monsoon. The Statistical Model reflects the global weather models indicating scarce chances of El Nino event.
El Niño’s Influence on Monsoon
El Nino is connected with the drying up of monsoon rain. In a regular year, there is a 33% chance of a typical monsoon which leads to high confidence that the 2020 monsoon will be normal.
El Nino’s Global Impact
El Nino has globally impacting effects, causing droughts in Australia, India, Southern Africa and floods in Peru, Ecuador, the United States, the Gulf of Mexico, and the Colorado River basin.
Southern Oscillation Index and El Nino Southern Oscillation
The Southern Oscillation Index (SOI) provides insights into the development and intensity of El Nino or La Nina events. Calculated based on the atmospheric pressure differences between the South Pacific Ocean and Australia, positive SOI values indicate La Nina conditions while negative values suggest El Nino conditions. The El Nino Southern Oscillation (ENSO) refers to the oscillation between El Nino and La Nina events, shifting irregularly every two to seven years.
Last Modified: February 7, 2024